Margaret Seton, MD

Paget disease of bone is a focal disorder of the aging skeleton that can be asymptomatic or can present with pain, bowing deformities, fractures, or nonspecific rheumatic complaints. Physicians often discover it in asymptomatic patients when serum alkaline phosphatase levels are elevated or as an incidental finding on radiography. Despite evidence of germline mutations and polymorphisms that predispose to Paget disease, the environmental determinants that permit disease expression in older people remain unknown.

A STRIKING GEOGRAPHIC DISTRIBUTION

Researchers have been studying the determinants and distribution of Paget disease ever since Sir James Paget first described it in 1877.¹

Paget disease has a predilection for the axial skeleton, particularly the lumbosacral spine and pelvis, as well as the skull, femur, and tibia.² Knowing this, investigators have used screening plain films of the abdomen (kidney-ureter-bladder views) to estimate its prevalence in different populations, as these images capture the lumbosacral spine, pelvis, and proximal femurs. Other means of assessing prevalence have included autopsy series, questionnaires, and screens for biochemical markers of bone turnover, such as elevated serum alkaline phosphatase from bone.^3–6

Using these methods, Paget disease has been estimated to occur in 1% to 3% of people over age 55, and in as many as 8% of people over age 80 in certain countries.⁷

This disease has a striking geographic distribution, being frequent in Europe, Canada, the United States, Australia, New Zealand, and cities of South America, but rare in Scandinavia and Japan. It seems to be equally rare in other countries of the Far East and in India, Russia, and Africa, although its prevalence in these areas has not been thoroughly investigated.⁸

That it is an ancient disease has been corroborated by excavations in churchyards in Great Britain.^9,10 It may be familial or sporadic, but its expression is delayed until late middle age in most persons, and it does not occur in children. For reasons unclear, the prevalence seems to be decreasing in many countries.^11–13

GENETICS IS NOT THE WHOLE STORY

The variable prevalence of Paget disease in different geographic regions and its sometimes-familial expression suggest a genetic predisposition, environmental factor, or both.

Mutations in SQSTM1

In 2002, scientists investigating a cohort of French Canadian families found a mutation in the SQSTM1 gene that was present in almost 50% of people with familial Paget disease and in 16% of those with sporadic Paget disease.¹⁴ Hocking and his colleagues in the United Kingdom subsequently found the same mutation in 19% of cases of familial Paget disease and in 9% of sporadic cases.¹⁵

Further, investigators noted that the mutation was often present on a conserved haplotype, consistent with a stable genetic change occurring in the affected population.¹⁶ This observation of a “founder effect” dovetailed with the epidemiology of Paget disease,¹⁷ but only with this SQSTM1 mutation.

Throughout Europe, Australia, and the United States, comparable rates of the SQSTM1 mutation were reported in or around the ubiquitin-associated domain. Several specific mutations exist, the most common one being P392L, ie, a prolineto-leucine substitution at amino acid 392. Scientists have tried to correlate severity of disease with genotype, but the findings have been inconsistent.^18–21

Investigations into the mechanism of disease have pointed to the role of p62, the product of SQSTM1, in signaling osteoclast activation via nuclear factor kappa B. Since this initial discovery, polymorphisms in the genes affecting osteoclast maturation, activation, and fusion pathways have been shown to predispose to Paget disease. Examples:

• TNFRSF11A, which codes for receptor activator of nuclear factor kappa B, or RANK
• TNFRSF11B, which codes for osteoprotegerin, or OPG
• CSF1, which codes for macrophage colony-stimulating factor 1, and
• OPTN, which codes for optineurin, a member of the nuclear factor kappa B-modulating protein family.

Clinicians interested in these details can read an excellent review of the pathogenesis of Paget disease.²²

Other possible factors

Although there is good evidence that measles and canine distemper virus can infect osteoclasts and modify their phenotype, there is no good evidence that these infections by themselves cause Paget disease.^23–25 It is, however, tempting to think of these RNA paramyxoviruses as precipitating factors; conceivably, an infectious agent might seed the ends of long bones, accounting for the fixed distribution of Paget disease and its late expression.

Epidemiologic studies from around the world have failed to identify conclusively any environmental exposure that predisposes to Paget disease, although a rural setting, trauma, infection, and milk ingestion have all been proposed.^26–28 It is also possible that as bone ages and the marrow becomes less cellular and more fatty, these changes may permit the disease to develop.

The greatest risk factor for Paget disease is perhaps aging, followed by ancestry and a known family history of it. That genetics is not the whole story is evident by reports of people with SQSTM1 mutations who show no clinical evidence of Paget disease in their old age, and patients with Paget disease who have no SQSTM1 mutation.^20,29

CLINICAL PRESENTATION

Most patients with Paget disease have no symptoms and come to medical attention because of an elevated serum alkaline phosphatase level or characteristic findings on radiographs ordered for other indications.¹¹ Paget disease is the second most common disorder of aging bone after osteoporosis. Yet unlike osteoporosis, which presents as a systemic fragility of bone, the clinical manifestations of Paget disease depend on which bones are affected and how enlarged or misshapen they have become.

Common complications

As a consequence of this abnormal bone remodeling and overgrowth, many patients present with bone pain. Bone deformity, headache, and hearing loss may also occur (Figure 1), as well as fractures and nerve compression syndromes (eg, spinal stenosis, sciatica, cauda equina syndrome).

It is important to remember that “pagetic” bone may not be the source of pain, and that functional impairment caused by degenerative changes at affected sites is common (Figure  2).^30,31

In a study from the New England Registry for Paget’s Disease,³² most patients knew fairly well which bones were affected and what complications resulted from this when deformity, fracture, or total joint replacement had occurred.³² Although Paget disease did affect their quality of life as measured by physical functioning on the Short Form-12 assessment, these impairments did not seem to affect their outlook, which was as good as or better than that in other people their age.

Metabolic complications

Metabolic complications of Paget disease are rare today but can occur in an elderly patient who has active, polyostotic (multibone) disease.³³ The accelerated rate of bone remodeling and the increased vascularity of pagetic bone have been reported to lead to high-output heart failure. In theory, treatment should ease this by diminishing blood flow to pagetic bone and restoring bone turnover to more normal levels.³⁴

Hypercalcemia can occur when patients with Paget disease are immobilized for any reason, and there is probably a higher incidence of renal stones in patients with Paget disease.^35,36

Malignant complications

Osteosarcoma rarely arises in pagetic bone. Yet Paget disease may account for a significant number of cases of this cancer in the elderly.³⁷ In these cases, osteosarcoma is presumed to be driven by a second genetic mutation, has a genetic signature distinct from that in osteosarcomas occurring in youth, and is quite resistant to treatment.³⁸ In Scandinavia and Japan, where Paget disease is rare, the second peak of osteosarcoma that occurs with aging seems muted as well.^39,40 These cancers present with pain, soft-tissue swelling, and variable elevations in serum alkaline phosphatase. Investigations to date suggest that pagetic lesions and osteosarcomas arising in pagetic bone are probably both driven to some extent by stromal cells overexpressing RANK ligand and may not represent defects intrinsic to the osteoclast.⁴¹

Giant-cell tumors of bone are also rare but can arise in pagetic bone. A cluster of cases was reported in Avellino and other towns of southern Italy.⁴² Again, the lesions occur in older individuals and in different sites than those seen in the benign giant-cell tumors recorded in patients without Paget disease.

Metastases from lymphomas, prostate cancer, and breast cancer certainly occur in bone, but rarely in pagetic sites.⁴³ A recent case study noted that patients with prostate cancer who also had Paget disease had a later onset of metastasis to bone than patients without coincident Paget disease.⁴⁴

A THOUGHTFUL ASSESSMENT

Evaluating a patient with Paget disease requires a thoughtful assessment of its musculoskeletal consequences in an aging skeleton. Pain in Paget disease is often multifactorial. In the elderly, end-stage degenerative disease of the spine, hip, and knees, mechanical instability, compression fractures of the spine, and neuropathies may compound the clinical picture. Therefore, a thorough evaluation is required to plan effective therapy.

Alkaline phosphatase and other markers

A screening serum alkaline phosphatase level is usually sufficient to measure bone turnover. Produced by osteoblasts, alkaline phosphatase is a marker of bone formation, but an imperfect one. Often it is elevated in active Paget disease—but not always.⁴⁵ Many patients have normal serum alkaline phosphatase levels, particularly if they have monostotic (single-bone) disease. It is unclear why, in a disorder marked by accelerated bone remodeling, the biochemical markers are inconsistent measures of bone turnover.

Research into biochemical markers of Paget disease has had two aims: to identify the single best marker for baseline assessment of pagetic bone activity and to find out whether this measurement responds to therapy.^46,47 Measures of bone formation such as bone-specific alkaline phosphatase, osteocalcin, and the procollagen type I peptides, and measures of bone resorption including the pyridinolines, hydroxyproline, and cross-linked collagens, have been analyzed as markers of bone remodeling and show no real advantage over the serum alkaline phosphatase level as reflections of bone turnover. As alkaline phosphatase measurement is inexpensive, available, and reliable, it should be used preferentially, with gamma-glutamyl transpeptidate or 5′ nucleotidase confirming the source as either liver or bone. Readers are directed to a recent review in which the utility of these markers is explored in more detail.⁴⁸

Imaging studies

Bone scans can give us an idea of the extent, location, and general activity of the disease (Figure 3). Uptake is avid in affected bones, beginning in the subchondral region and spreading throughout the bone. Bone scans can be particularly useful in defining sites of active disease when the serum alkaline phosphatase level is normal.

Plain radiography of the affected bones outlines the anatomy of the problem and gives some insight into the cause of pain (Figure 3).

Computed tomography or magnetic resonance imaging may prove useful in cases of spinal stenosis, cauda equina syndrome, compression fractures, or suspected malignancy (Figure  4), but these studies are expensive and generally are not needed.

Radiographic features. Paget disease is presumed to be a disease of the osteoclast, and the earliest lesion is described as lytic. In my own experience, it is unusual to see a purely lytic lesion, although sometimes the disease presents in the skull in this way—osteoporosis circumscripta—or in the femur or tibia with an advancing edge of pure osteolysis.

More often, one sees evidence of both resorption by osteoclasts and formation by osteoblasts, reflecting the coupling of these two processes in this disease. Radiographic findings on plain films are usually definitive, showing enlargement of the affected bone, deformity, coarsened trabeculae, and thickened cortices with tunneling (Figure 5).⁴⁹ In weightbearing bones, pseudofractures may stud the convex surface. These incongruities of bone may persist for years, heralding fracture only when there is focal pain (Figure 6).⁵⁰

Biopsy is infrequently needed

If these diagnostic findings are not present, then biopsy is indicated. In the United Sates and Canada, where Paget disease is fairly common, biopsy is infrequently needed and is usually reserved for situations in which the differential diagnosis includes cancer, as when the cortex cannot be clearly visualized, the lesions are atypical in pattern or location, or there is a single sclerotic vertebral body on imaging.⁵¹

The other indication for biopsy is a “new” pagetic lesion. For reasons unknown, the pattern of skeletal involvement in Paget disease tends to be stable throughout the patient’s lifetime. This is another reason why a baseline bone scan is useful.

TREATMENT WITH BISPHOSPHONATES

Treatment of Paget disease today relies for the most part on the new generation of nitrogen-containing bisphosphonates. As a class, these are antiresorptive agents that inhibit osteoclasts; in this way they slow bone remodeling and enhance the deposition of normal lamellar bone. Their clinical efficacy in Paget disease, coupled with the observation that the earliest lesion in Paget disease is lytic, underscores the principle that Paget disease is a disorder of the osteoclast.

Oral bisphosphonates

Etidronate, approved in 1977, was the first bisphosphonate licensed to treat Paget disease, and it remains available for this indication in the United States. Used in 6-month regimens, it lowers the serum alkaline phosphatase level in some patients, but it has a narrow therapeutic margin. Drug-induced osteomalacia and worsening lytic lesions and fractures in weight-bearing bones are some of the complications.⁵² When the nitrogen-containing bisphosphonates were developed, they proved to be more potent antiresorptive agents that pose less risk of mineralization defects at prescribed doses.

Alendronate, approved in 1995, is an oral nitrogen-containing bisphosphonate that is effective in treating Paget disease.⁵³ Alendronate is now available in the United States only through special programs (eg, the CVS ProCare Program); the paperwork required to secure this drug is onerous, so the drug is used infrequently. Studies in Paget disease showed that it normalizes the serum alkaline phosphatase level, improves the radiographic appearance, and eases pain in many patients.⁵⁴ The dosage is 40 mg daily for 6 months.

Risedronate, approved in 1998, is another oral nitrogen-containing bisphosphonate and is comparable to alendronate in efficacy.⁵⁵ The dosage is 30 mg daily for 2 months.

Tiludronate is another oral bisphosphonate with a different mechanism of action from the nitrogen-containing bisphosphonates.⁵⁶ It is safe, often effective, but less potent than the newer agents.

The oral bisphosphonates are well tolerated, with few side effects other than gastrointestinal distress. As a class, they are poorly absorbed and so must be taken fasting with a full glass of water on rising, after which the patient should remain upright without food or drink for 30 to 60 minutes. This is a nuisance for elderly patients already on multiple medications and thus makes intravenous agents appealing.

Intravenous bisphosphonates

Pamidronate was approved in 1994. It is quite effective in many patients with Paget disease. There is no consensus around the world on dosing, with regimens ranging from 30 mg to 90 mg or more intravenously in divided doses given over 2 to 4 hours from once a day to once a week. In the United States, 30 mg is given over 4 hours on 3 consecutive days. Resistance to pamidronate has been described; the mechanism is unknown.

Zoledronic acid is a nitrogen-containing bisphosphonate. It is given as a single infusion over 15 minutes, and re-treatment may not be necessary for years. A randomized clinical trial in 2005 demonstrated the efficacy of zoledronic acid 5 mg by infusion compared with oral risedronate in the treatment of Paget disease.⁵⁷ In observational extension studies lasting as long as 6.5 years, zoledronic acid has been shown to be superior to risedronate in terms of the proportion of patients experiencing a sustained clinical remission.⁵⁸

While there are many bisphosphonates on the market, an infusion of 5 mg of zoledronic acid seems optimal in most patients who do not have a contraindication or an aversion to intravenous therapy. It tends to normalize the serum alkaline phosphatase level quickly and to leave more patients in sustained biochemical remission than do older bisphosphonates, as noted above. It also tends to be more effective in normalizing the serum alkaline phosphatase level when a patient has used other bisphosphonates in the past or has become resistant to them.

Bisphosphonates reduce bone turnover but do not correct deformities

In randomized clinical trials, bisphosphonates have been shown to restore bone remodeling to more normal levels, to ease pain from pagetic bone, to lower the serum alkaline phosphatase level, and to heal radiographic lesions, but these drugs have not been proven to prevent progression of deformity or to restore the structural integrity of bone (Figure 6).

The Paget’s Disease: Randomized Trial of Intensive Versus Symptomatic Management (PRISM), in 1,324 people with Paget disease in the United Kingdom, showed no difference in the incidence of fracture, orthopedic surgery, quality of life, or hearing thresholds over 2 to 5 years in patients treated with bisphosphonates vs those treated symptomatically, despite a significant difference in serum alkaline phosphatase in the two groups (P < .001).⁵⁹

In the observational extension study of zoledronic acid described above,⁵⁸ three of four fractures occurred in the group treated with zoledronic acid, echoing the findings of the PRISM study.

Adverse effects of bisphosphonates

The more potent the bisphosphonate is as an antiresorptive agent, the more it suppresses normal bone remodeling, which can lead to osteonecrosis of the jaw and to atypical femoral fractures.^60,61 These complications are unusual in patients with Paget disease because the treatment is intermittent. Sometimes a single dose of zoledronic acid or one course of risedronate or alendronate will last for years.

All the nitrogen-containing bisphosphonates, particularly zoledronic acid, may provoke flulike symptoms of fever, arthralgias, and bone pain. This effect is self-limited, resolves in days, and does not tend to recur. Bone pain may be more sustained, but this also passes, and within weeks the antiresorptive process has abated and pagetic bone pain will ease. Atrial fibrillation is not an anticipated complication of treatment with a bisphosphonate.⁶² The risk of esophageal cancer is not confirmed at this time.⁶³ Other rare complications of the bisphosphonates include iritis, acute renal failure, and allergy.

Bisphosphonates are not approved for use in patients with creatinine clearance less than 30 mL/min, or in pregnancy.

Other treatments

Calcitonin, an older agent, can still be useful in easing the pain of Paget disease, healing bone lesions, and reducing the metabolic activity of pagetic bone in patients who cannot receive bisphosphonates. It is given by injection in doses of 50 to 100 IU daily or every other day. Although unlikely to effect a sustained clinical remission, calcitonin remains a safe, well-tolerated, and well-studied medication in Paget disease and is approved for this indication.^64,65

Denosumab has not been formally studied in Paget disease, but a recent case report indicated it was effective.⁶⁶

A conservative strategy

Guidelines for treating Paget disease have been written at various times in many countries, including Italy (2007),⁶⁷ the United Kingdom (2004),⁶⁸ Japan (2006),⁶⁹ and Canada (2007).⁷⁰ Recommendations differ, in part because it is hard to ascertain whether long-term outcomes are improved by treatment, and in part because the prevalence of Paget disease is decreasing and its severity is lessening.^11,12 Some guidelines are outdated, since they do not include the newer bisphosphonates.

If the natural history of untreated Paget disease involves the gradual evolution over more than 20 years of bowing deformities in the lower limbs, rigidity and overgrowth of the spine, and softening and enlargement of the skull, as described by Sir James Paget, then treatment should be initiated in hopes that it will modify the outcome. We have no lens to better focus this question on the effect of treatment on the natural history of the disease. We have the PRISM study, designed before zoledronic acid was approved and only 2 to 5 years in duration. And we have the epidemiologic data demonstrating that most patients have no symptoms during their lifetime.

We see the crippling bone disease described by Sir James Paget so infrequently today in the United States that we forget the profound morbidity that may attend the skeletal changes of Paget disease that were common in the early 20th century. Once the bones of the skull are overgrown, the limbs are bowed, and the degenerative joint disease is present, no medication can reverse these changes. Then, the integrity of the bone is lost, and the vulnerability to fracture, early osteoarthritis, nerve compression syndromes, and hearing loss persist. Understanding these consequences prompts the recommendation of early treatment in patients with Paget disease, in hopes of mitigating disease progression.

Patients with active Paget disease, documented either by an elevated serum alkaline phosphatase or by a bone scan, should be treated with a bisphosphonate if the disease is found in sites where remodeling of bone may lead to complications. Such sites include the skull, spine, and long bones of the lower extremity. Paget disease of bone in the pelvis tends to give little trouble (Figure 2) unless it is proximal to a joint, when pain and early arthritis may result. Treatment is safe and, I think, prudent to undertake in any person over age 55 with active disease. To prevent hypocalcemia during treatment, all patients should be repleted with vitamin D and maintained on calcium 1,200 mg daily through diet or supplements with meals.

Throughout the evaluation and treatment, it is important to remember that pain may not emanate from pagetic bone. If medication for Paget disease proves ineffective in the first few months, analgesics, bracing, walking aids, and operative management⁷¹ are adjunctive therapies to improve the functional status of these patients.

It is a remarkable clinical observation that treatment of Paget disease may rapidly reverse neurologic syndromes, resolve the erythema or warmth overlying active pagetic bone, and diminish the risk of bleeding with surgery. This response to therapy suggests that there is prompt inhibition and apoptosis of the osteoclasts, accompanied by diminished vascularity of bone. Whatever the mechanism, it is worth treating patients who have spinal stenosis, arthritis, and nerve compression syndromes with calcitonin or bisphosphonates before surgical intervention, whenever possible.^34,72

Paget disease of bone is a focal disorder of the aging skeleton that can be asymptomatic or can present with pain, bowing deformities, fractures, or nonspecific rheumatic complaints. Physicians often discover it in asymptomatic patients when serum alkaline phosphatase levels are elevated or as an incidental finding on radiography. Despite evidence of germline mutations and polymorphisms that predispose to Paget disease, the environmental determinants that permit disease expression in older people remain unknown.

A STRIKING GEOGRAPHIC DISTRIBUTION

Researchers have been studying the determinants and distribution of Paget disease ever since Sir James Paget first described it in 1877.¹

Paget disease has a predilection for the axial skeleton, particularly the lumbosacral spine and pelvis, as well as the skull, femur, and tibia.² Knowing this, investigators have used screening plain films of the abdomen (kidney-ureter-bladder views) to estimate its prevalence in different populations, as these images capture the lumbosacral spine, pelvis, and proximal femurs. Other means of assessing prevalence have included autopsy series, questionnaires, and screens for biochemical markers of bone turnover, such as elevated serum alkaline phosphatase from bone.^3–6

Using these methods, Paget disease has been estimated to occur in 1% to 3% of people over age 55, and in as many as 8% of people over age 80 in certain countries.⁷

This disease has a striking geographic distribution, being frequent in Europe, Canada, the United States, Australia, New Zealand, and cities of South America, but rare in Scandinavia and Japan. It seems to be equally rare in other countries of the Far East and in India, Russia, and Africa, although its prevalence in these areas has not been thoroughly investigated.⁸

That it is an ancient disease has been corroborated by excavations in churchyards in Great Britain.^9,10 It may be familial or sporadic, but its expression is delayed until late middle age in most persons, and it does not occur in children. For reasons unclear, the prevalence seems to be decreasing in many countries.^11–13

GENETICS IS NOT THE WHOLE STORY

The variable prevalence of Paget disease in different geographic regions and its sometimes-familial expression suggest a genetic predisposition, environmental factor, or both.

Mutations in SQSTM1

In 2002, scientists investigating a cohort of French Canadian families found a mutation in the SQSTM1 gene that was present in almost 50% of people with familial Paget disease and in 16% of those with sporadic Paget disease.¹⁴ Hocking and his colleagues in the United Kingdom subsequently found the same mutation in 19% of cases of familial Paget disease and in 9% of sporadic cases.¹⁵

Further, investigators noted that the mutation was often present on a conserved haplotype, consistent with a stable genetic change occurring in the affected population.¹⁶ This observation of a “founder effect” dovetailed with the epidemiology of Paget disease,¹⁷ but only with this SQSTM1 mutation.

Throughout Europe, Australia, and the United States, comparable rates of the SQSTM1 mutation were reported in or around the ubiquitin-associated domain. Several specific mutations exist, the most common one being P392L, ie, a prolineto-leucine substitution at amino acid 392. Scientists have tried to correlate severity of disease with genotype, but the findings have been inconsistent.^18–21

Investigations into the mechanism of disease have pointed to the role of p62, the product of SQSTM1, in signaling osteoclast activation via nuclear factor kappa B. Since this initial discovery, polymorphisms in the genes affecting osteoclast maturation, activation, and fusion pathways have been shown to predispose to Paget disease. Examples:

• TNFRSF11A, which codes for receptor activator of nuclear factor kappa B, or RANK
• TNFRSF11B, which codes for osteoprotegerin, or OPG
• CSF1, which codes for macrophage colony-stimulating factor 1, and
• OPTN, which codes for optineurin, a member of the nuclear factor kappa B-modulating protein family.

Clinicians interested in these details can read an excellent review of the pathogenesis of Paget disease.²²

Other possible factors

Although there is good evidence that measles and canine distemper virus can infect osteoclasts and modify their phenotype, there is no good evidence that these infections by themselves cause Paget disease.^23–25 It is, however, tempting to think of these RNA paramyxoviruses as precipitating factors; conceivably, an infectious agent might seed the ends of long bones, accounting for the fixed distribution of Paget disease and its late expression.

Epidemiologic studies from around the world have failed to identify conclusively any environmental exposure that predisposes to Paget disease, although a rural setting, trauma, infection, and milk ingestion have all been proposed.^26–28 It is also possible that as bone ages and the marrow becomes less cellular and more fatty, these changes may permit the disease to develop.

The greatest risk factor for Paget disease is perhaps aging, followed by ancestry and a known family history of it. That genetics is not the whole story is evident by reports of people with SQSTM1 mutations who show no clinical evidence of Paget disease in their old age, and patients with Paget disease who have no SQSTM1 mutation.^20,29

CLINICAL PRESENTATION

Most patients with Paget disease have no symptoms and come to medical attention because of an elevated serum alkaline phosphatase level or characteristic findings on radiographs ordered for other indications.¹¹ Paget disease is the second most common disorder of aging bone after osteoporosis. Yet unlike osteoporosis, which presents as a systemic fragility of bone, the clinical manifestations of Paget disease depend on which bones are affected and how enlarged or misshapen they have become.

Common complications

As a consequence of this abnormal bone remodeling and overgrowth, many patients present with bone pain. Bone deformity, headache, and hearing loss may also occur (Figure 1), as well as fractures and nerve compression syndromes (eg, spinal stenosis, sciatica, cauda equina syndrome).

It is important to remember that “pagetic” bone may not be the source of pain, and that functional impairment caused by degenerative changes at affected sites is common (Figure  2).^30,31

In a study from the New England Registry for Paget’s Disease,³² most patients knew fairly well which bones were affected and what complications resulted from this when deformity, fracture, or total joint replacement had occurred.³² Although Paget disease did affect their quality of life as measured by physical functioning on the Short Form-12 assessment, these impairments did not seem to affect their outlook, which was as good as or better than that in other people their age.

Metabolic complications

Metabolic complications of Paget disease are rare today but can occur in an elderly patient who has active, polyostotic (multibone) disease.³³ The accelerated rate of bone remodeling and the increased vascularity of pagetic bone have been reported to lead to high-output heart failure. In theory, treatment should ease this by diminishing blood flow to pagetic bone and restoring bone turnover to more normal levels.³⁴

Hypercalcemia can occur when patients with Paget disease are immobilized for any reason, and there is probably a higher incidence of renal stones in patients with Paget disease.^35,36

Malignant complications

Osteosarcoma rarely arises in pagetic bone. Yet Paget disease may account for a significant number of cases of this cancer in the elderly.³⁷ In these cases, osteosarcoma is presumed to be driven by a second genetic mutation, has a genetic signature distinct from that in osteosarcomas occurring in youth, and is quite resistant to treatment.³⁸ In Scandinavia and Japan, where Paget disease is rare, the second peak of osteosarcoma that occurs with aging seems muted as well.^39,40 These cancers present with pain, soft-tissue swelling, and variable elevations in serum alkaline phosphatase. Investigations to date suggest that pagetic lesions and osteosarcomas arising in pagetic bone are probably both driven to some extent by stromal cells overexpressing RANK ligand and may not represent defects intrinsic to the osteoclast.⁴¹

Giant-cell tumors of bone are also rare but can arise in pagetic bone. A cluster of cases was reported in Avellino and other towns of southern Italy.⁴² Again, the lesions occur in older individuals and in different sites than those seen in the benign giant-cell tumors recorded in patients without Paget disease.

Metastases from lymphomas, prostate cancer, and breast cancer certainly occur in bone, but rarely in pagetic sites.⁴³ A recent case study noted that patients with prostate cancer who also had Paget disease had a later onset of metastasis to bone than patients without coincident Paget disease.⁴⁴

A THOUGHTFUL ASSESSMENT

Evaluating a patient with Paget disease requires a thoughtful assessment of its musculoskeletal consequences in an aging skeleton. Pain in Paget disease is often multifactorial. In the elderly, end-stage degenerative disease of the spine, hip, and knees, mechanical instability, compression fractures of the spine, and neuropathies may compound the clinical picture. Therefore, a thorough evaluation is required to plan effective therapy.

Alkaline phosphatase and other markers

A screening serum alkaline phosphatase level is usually sufficient to measure bone turnover. Produced by osteoblasts, alkaline phosphatase is a marker of bone formation, but an imperfect one. Often it is elevated in active Paget disease—but not always.⁴⁵ Many patients have normal serum alkaline phosphatase levels, particularly if they have monostotic (single-bone) disease. It is unclear why, in a disorder marked by accelerated bone remodeling, the biochemical markers are inconsistent measures of bone turnover.

Research into biochemical markers of Paget disease has had two aims: to identify the single best marker for baseline assessment of pagetic bone activity and to find out whether this measurement responds to therapy.^46,47 Measures of bone formation such as bone-specific alkaline phosphatase, osteocalcin, and the procollagen type I peptides, and measures of bone resorption including the pyridinolines, hydroxyproline, and cross-linked collagens, have been analyzed as markers of bone remodeling and show no real advantage over the serum alkaline phosphatase level as reflections of bone turnover. As alkaline phosphatase measurement is inexpensive, available, and reliable, it should be used preferentially, with gamma-glutamyl transpeptidate or 5′ nucleotidase confirming the source as either liver or bone. Readers are directed to a recent review in which the utility of these markers is explored in more detail.⁴⁸

Imaging studies

Bone scans can give us an idea of the extent, location, and general activity of the disease (Figure 3). Uptake is avid in affected bones, beginning in the subchondral region and spreading throughout the bone. Bone scans can be particularly useful in defining sites of active disease when the serum alkaline phosphatase level is normal.

Plain radiography of the affected bones outlines the anatomy of the problem and gives some insight into the cause of pain (Figure 3).

Computed tomography or magnetic resonance imaging may prove useful in cases of spinal stenosis, cauda equina syndrome, compression fractures, or suspected malignancy (Figure  4), but these studies are expensive and generally are not needed.

Radiographic features. Paget disease is presumed to be a disease of the osteoclast, and the earliest lesion is described as lytic. In my own experience, it is unusual to see a purely lytic lesion, although sometimes the disease presents in the skull in this way—osteoporosis circumscripta—or in the femur or tibia with an advancing edge of pure osteolysis.

More often, one sees evidence of both resorption by osteoclasts and formation by osteoblasts, reflecting the coupling of these two processes in this disease. Radiographic findings on plain films are usually definitive, showing enlargement of the affected bone, deformity, coarsened trabeculae, and thickened cortices with tunneling (Figure 5).⁴⁹ In weightbearing bones, pseudofractures may stud the convex surface. These incongruities of bone may persist for years, heralding fracture only when there is focal pain (Figure 6).⁵⁰

Biopsy is infrequently needed

If these diagnostic findings are not present, then biopsy is indicated. In the United Sates and Canada, where Paget disease is fairly common, biopsy is infrequently needed and is usually reserved for situations in which the differential diagnosis includes cancer, as when the cortex cannot be clearly visualized, the lesions are atypical in pattern or location, or there is a single sclerotic vertebral body on imaging.⁵¹

The other indication for biopsy is a “new” pagetic lesion. For reasons unknown, the pattern of skeletal involvement in Paget disease tends to be stable throughout the patient’s lifetime. This is another reason why a baseline bone scan is useful.

TREATMENT WITH BISPHOSPHONATES

Treatment of Paget disease today relies for the most part on the new generation of nitrogen-containing bisphosphonates. As a class, these are antiresorptive agents that inhibit osteoclasts; in this way they slow bone remodeling and enhance the deposition of normal lamellar bone. Their clinical efficacy in Paget disease, coupled with the observation that the earliest lesion in Paget disease is lytic, underscores the principle that Paget disease is a disorder of the osteoclast.

Oral bisphosphonates

Etidronate, approved in 1977, was the first bisphosphonate licensed to treat Paget disease, and it remains available for this indication in the United States. Used in 6-month regimens, it lowers the serum alkaline phosphatase level in some patients, but it has a narrow therapeutic margin. Drug-induced osteomalacia and worsening lytic lesions and fractures in weight-bearing bones are some of the complications.⁵² When the nitrogen-containing bisphosphonates were developed, they proved to be more potent antiresorptive agents that pose less risk of mineralization defects at prescribed doses.

Alendronate, approved in 1995, is an oral nitrogen-containing bisphosphonate that is effective in treating Paget disease.⁵³ Alendronate is now available in the United States only through special programs (eg, the CVS ProCare Program); the paperwork required to secure this drug is onerous, so the drug is used infrequently. Studies in Paget disease showed that it normalizes the serum alkaline phosphatase level, improves the radiographic appearance, and eases pain in many patients.⁵⁴ The dosage is 40 mg daily for 6 months.

Risedronate, approved in 1998, is another oral nitrogen-containing bisphosphonate and is comparable to alendronate in efficacy.⁵⁵ The dosage is 30 mg daily for 2 months.

Tiludronate is another oral bisphosphonate with a different mechanism of action from the nitrogen-containing bisphosphonates.⁵⁶ It is safe, often effective, but less potent than the newer agents.

The oral bisphosphonates are well tolerated, with few side effects other than gastrointestinal distress. As a class, they are poorly absorbed and so must be taken fasting with a full glass of water on rising, after which the patient should remain upright without food or drink for 30 to 60 minutes. This is a nuisance for elderly patients already on multiple medications and thus makes intravenous agents appealing.

Intravenous bisphosphonates

Pamidronate was approved in 1994. It is quite effective in many patients with Paget disease. There is no consensus around the world on dosing, with regimens ranging from 30 mg to 90 mg or more intravenously in divided doses given over 2 to 4 hours from once a day to once a week. In the United States, 30 mg is given over 4 hours on 3 consecutive days. Resistance to pamidronate has been described; the mechanism is unknown.

Zoledronic acid is a nitrogen-containing bisphosphonate. It is given as a single infusion over 15 minutes, and re-treatment may not be necessary for years. A randomized clinical trial in 2005 demonstrated the efficacy of zoledronic acid 5 mg by infusion compared with oral risedronate in the treatment of Paget disease.⁵⁷ In observational extension studies lasting as long as 6.5 years, zoledronic acid has been shown to be superior to risedronate in terms of the proportion of patients experiencing a sustained clinical remission.⁵⁸

While there are many bisphosphonates on the market, an infusion of 5 mg of zoledronic acid seems optimal in most patients who do not have a contraindication or an aversion to intravenous therapy. It tends to normalize the serum alkaline phosphatase level quickly and to leave more patients in sustained biochemical remission than do older bisphosphonates, as noted above. It also tends to be more effective in normalizing the serum alkaline phosphatase level when a patient has used other bisphosphonates in the past or has become resistant to them.

Bisphosphonates reduce bone turnover but do not correct deformities

In randomized clinical trials, bisphosphonates have been shown to restore bone remodeling to more normal levels, to ease pain from pagetic bone, to lower the serum alkaline phosphatase level, and to heal radiographic lesions, but these drugs have not been proven to prevent progression of deformity or to restore the structural integrity of bone (Figure 6).

The Paget’s Disease: Randomized Trial of Intensive Versus Symptomatic Management (PRISM), in 1,324 people with Paget disease in the United Kingdom, showed no difference in the incidence of fracture, orthopedic surgery, quality of life, or hearing thresholds over 2 to 5 years in patients treated with bisphosphonates vs those treated symptomatically, despite a significant difference in serum alkaline phosphatase in the two groups (P < .001).⁵⁹

In the observational extension study of zoledronic acid described above,⁵⁸ three of four fractures occurred in the group treated with zoledronic acid, echoing the findings of the PRISM study.

Adverse effects of bisphosphonates

The more potent the bisphosphonate is as an antiresorptive agent, the more it suppresses normal bone remodeling, which can lead to osteonecrosis of the jaw and to atypical femoral fractures.^60,61 These complications are unusual in patients with Paget disease because the treatment is intermittent. Sometimes a single dose of zoledronic acid or one course of risedronate or alendronate will last for years.

All the nitrogen-containing bisphosphonates, particularly zoledronic acid, may provoke flulike symptoms of fever, arthralgias, and bone pain. This effect is self-limited, resolves in days, and does not tend to recur. Bone pain may be more sustained, but this also passes, and within weeks the antiresorptive process has abated and pagetic bone pain will ease. Atrial fibrillation is not an anticipated complication of treatment with a bisphosphonate.⁶² The risk of esophageal cancer is not confirmed at this time.⁶³ Other rare complications of the bisphosphonates include iritis, acute renal failure, and allergy.

Bisphosphonates are not approved for use in patients with creatinine clearance less than 30 mL/min, or in pregnancy.

Other treatments

Calcitonin, an older agent, can still be useful in easing the pain of Paget disease, healing bone lesions, and reducing the metabolic activity of pagetic bone in patients who cannot receive bisphosphonates. It is given by injection in doses of 50 to 100 IU daily or every other day. Although unlikely to effect a sustained clinical remission, calcitonin remains a safe, well-tolerated, and well-studied medication in Paget disease and is approved for this indication.^64,65

Denosumab has not been formally studied in Paget disease, but a recent case report indicated it was effective.⁶⁶

A conservative strategy

Guidelines for treating Paget disease have been written at various times in many countries, including Italy (2007),⁶⁷ the United Kingdom (2004),⁶⁸ Japan (2006),⁶⁹ and Canada (2007).⁷⁰ Recommendations differ, in part because it is hard to ascertain whether long-term outcomes are improved by treatment, and in part because the prevalence of Paget disease is decreasing and its severity is lessening.^11,12 Some guidelines are outdated, since they do not include the newer bisphosphonates.

If the natural history of untreated Paget disease involves the gradual evolution over more than 20 years of bowing deformities in the lower limbs, rigidity and overgrowth of the spine, and softening and enlargement of the skull, as described by Sir James Paget, then treatment should be initiated in hopes that it will modify the outcome. We have no lens to better focus this question on the effect of treatment on the natural history of the disease. We have the PRISM study, designed before zoledronic acid was approved and only 2 to 5 years in duration. And we have the epidemiologic data demonstrating that most patients have no symptoms during their lifetime.

We see the crippling bone disease described by Sir James Paget so infrequently today in the United States that we forget the profound morbidity that may attend the skeletal changes of Paget disease that were common in the early 20th century. Once the bones of the skull are overgrown, the limbs are bowed, and the degenerative joint disease is present, no medication can reverse these changes. Then, the integrity of the bone is lost, and the vulnerability to fracture, early osteoarthritis, nerve compression syndromes, and hearing loss persist. Understanding these consequences prompts the recommendation of early treatment in patients with Paget disease, in hopes of mitigating disease progression.

Patients with active Paget disease, documented either by an elevated serum alkaline phosphatase or by a bone scan, should be treated with a bisphosphonate if the disease is found in sites where remodeling of bone may lead to complications. Such sites include the skull, spine, and long bones of the lower extremity. Paget disease of bone in the pelvis tends to give little trouble (Figure 2) unless it is proximal to a joint, when pain and early arthritis may result. Treatment is safe and, I think, prudent to undertake in any person over age 55 with active disease. To prevent hypocalcemia during treatment, all patients should be repleted with vitamin D and maintained on calcium 1,200 mg daily through diet or supplements with meals.

Throughout the evaluation and treatment, it is important to remember that pain may not emanate from pagetic bone. If medication for Paget disease proves ineffective in the first few months, analgesics, bracing, walking aids, and operative management⁷¹ are adjunctive therapies to improve the functional status of these patients.

It is a remarkable clinical observation that treatment of Paget disease may rapidly reverse neurologic syndromes, resolve the erythema or warmth overlying active pagetic bone, and diminish the risk of bleeding with surgery. This response to therapy suggests that there is prompt inhibition and apoptosis of the osteoclasts, accompanied by diminished vascularity of bone. Whatever the mechanism, it is worth treating patients who have spinal stenosis, arthritis, and nerve compression syndromes with calcitonin or bisphosphonates before surgical intervention, whenever possible.^34,72

Paget disease of bone is a focal disorder of the aging skeleton that can be asymptomatic or can present with pain, bowing deformities, fractures, or nonspecific rheumatic complaints. Physicians often discover it in asymptomatic patients when serum alkaline phosphatase levels are elevated or as an incidental finding on radiography. Despite evidence of germline mutations and polymorphisms that predispose to Paget disease, the environmental determinants that permit disease expression in older people remain unknown.

A STRIKING GEOGRAPHIC DISTRIBUTION

Researchers have been studying the determinants and distribution of Paget disease ever since Sir James Paget first described it in 1877.¹

Paget disease has a predilection for the axial skeleton, particularly the lumbosacral spine and pelvis, as well as the skull, femur, and tibia.² Knowing this, investigators have used screening plain films of the abdomen (kidney-ureter-bladder views) to estimate its prevalence in different populations, as these images capture the lumbosacral spine, pelvis, and proximal femurs. Other means of assessing prevalence have included autopsy series, questionnaires, and screens for biochemical markers of bone turnover, such as elevated serum alkaline phosphatase from bone.^3–6

Using these methods, Paget disease has been estimated to occur in 1% to 3% of people over age 55, and in as many as 8% of people over age 80 in certain countries.⁷

This disease has a striking geographic distribution, being frequent in Europe, Canada, the United States, Australia, New Zealand, and cities of South America, but rare in Scandinavia and Japan. It seems to be equally rare in other countries of the Far East and in India, Russia, and Africa, although its prevalence in these areas has not been thoroughly investigated.⁸

That it is an ancient disease has been corroborated by excavations in churchyards in Great Britain.^9,10 It may be familial or sporadic, but its expression is delayed until late middle age in most persons, and it does not occur in children. For reasons unclear, the prevalence seems to be decreasing in many countries.^11–13

GENETICS IS NOT THE WHOLE STORY

The variable prevalence of Paget disease in different geographic regions and its sometimes-familial expression suggest a genetic predisposition, environmental factor, or both.

Mutations in SQSTM1

In 2002, scientists investigating a cohort of French Canadian families found a mutation in the SQSTM1 gene that was present in almost 50% of people with familial Paget disease and in 16% of those with sporadic Paget disease.¹⁴ Hocking and his colleagues in the United Kingdom subsequently found the same mutation in 19% of cases of familial Paget disease and in 9% of sporadic cases.¹⁵

Further, investigators noted that the mutation was often present on a conserved haplotype, consistent with a stable genetic change occurring in the affected population.¹⁶ This observation of a “founder effect” dovetailed with the epidemiology of Paget disease,¹⁷ but only with this SQSTM1 mutation.

Throughout Europe, Australia, and the United States, comparable rates of the SQSTM1 mutation were reported in or around the ubiquitin-associated domain. Several specific mutations exist, the most common one being P392L, ie, a prolineto-leucine substitution at amino acid 392. Scientists have tried to correlate severity of disease with genotype, but the findings have been inconsistent.^18–21

Investigations into the mechanism of disease have pointed to the role of p62, the product of SQSTM1, in signaling osteoclast activation via nuclear factor kappa B. Since this initial discovery, polymorphisms in the genes affecting osteoclast maturation, activation, and fusion pathways have been shown to predispose to Paget disease. Examples:

• TNFRSF11A, which codes for receptor activator of nuclear factor kappa B, or RANK
• TNFRSF11B, which codes for osteoprotegerin, or OPG
• CSF1, which codes for macrophage colony-stimulating factor 1, and
• OPTN, which codes for optineurin, a member of the nuclear factor kappa B-modulating protein family.

Clinicians interested in these details can read an excellent review of the pathogenesis of Paget disease.²²

Other possible factors

Although there is good evidence that measles and canine distemper virus can infect osteoclasts and modify their phenotype, there is no good evidence that these infections by themselves cause Paget disease.^23–25 It is, however, tempting to think of these RNA paramyxoviruses as precipitating factors; conceivably, an infectious agent might seed the ends of long bones, accounting for the fixed distribution of Paget disease and its late expression.

Epidemiologic studies from around the world have failed to identify conclusively any environmental exposure that predisposes to Paget disease, although a rural setting, trauma, infection, and milk ingestion have all been proposed.^26–28 It is also possible that as bone ages and the marrow becomes less cellular and more fatty, these changes may permit the disease to develop.

The greatest risk factor for Paget disease is perhaps aging, followed by ancestry and a known family history of it. That genetics is not the whole story is evident by reports of people with SQSTM1 mutations who show no clinical evidence of Paget disease in their old age, and patients with Paget disease who have no SQSTM1 mutation.^20,29

CLINICAL PRESENTATION

Most patients with Paget disease have no symptoms and come to medical attention because of an elevated serum alkaline phosphatase level or characteristic findings on radiographs ordered for other indications.¹¹ Paget disease is the second most common disorder of aging bone after osteoporosis. Yet unlike osteoporosis, which presents as a systemic fragility of bone, the clinical manifestations of Paget disease depend on which bones are affected and how enlarged or misshapen they have become.

Common complications

As a consequence of this abnormal bone remodeling and overgrowth, many patients present with bone pain. Bone deformity, headache, and hearing loss may also occur (Figure 1), as well as fractures and nerve compression syndromes (eg, spinal stenosis, sciatica, cauda equina syndrome).

It is important to remember that “pagetic” bone may not be the source of pain, and that functional impairment caused by degenerative changes at affected sites is common (Figure  2).^30,31

In a study from the New England Registry for Paget’s Disease,³² most patients knew fairly well which bones were affected and what complications resulted from this when deformity, fracture, or total joint replacement had occurred.³² Although Paget disease did affect their quality of life as measured by physical functioning on the Short Form-12 assessment, these impairments did not seem to affect their outlook, which was as good as or better than that in other people their age.

Metabolic complications

Metabolic complications of Paget disease are rare today but can occur in an elderly patient who has active, polyostotic (multibone) disease.³³ The accelerated rate of bone remodeling and the increased vascularity of pagetic bone have been reported to lead to high-output heart failure. In theory, treatment should ease this by diminishing blood flow to pagetic bone and restoring bone turnover to more normal levels.³⁴

Hypercalcemia can occur when patients with Paget disease are immobilized for any reason, and there is probably a higher incidence of renal stones in patients with Paget disease.^35,36

Malignant complications

Osteosarcoma rarely arises in pagetic bone. Yet Paget disease may account for a significant number of cases of this cancer in the elderly.³⁷ In these cases, osteosarcoma is presumed to be driven by a second genetic mutation, has a genetic signature distinct from that in osteosarcomas occurring in youth, and is quite resistant to treatment.³⁸ In Scandinavia and Japan, where Paget disease is rare, the second peak of osteosarcoma that occurs with aging seems muted as well.^39,40 These cancers present with pain, soft-tissue swelling, and variable elevations in serum alkaline phosphatase. Investigations to date suggest that pagetic lesions and osteosarcomas arising in pagetic bone are probably both driven to some extent by stromal cells overexpressing RANK ligand and may not represent defects intrinsic to the osteoclast.⁴¹

Giant-cell tumors of bone are also rare but can arise in pagetic bone. A cluster of cases was reported in Avellino and other towns of southern Italy.⁴² Again, the lesions occur in older individuals and in different sites than those seen in the benign giant-cell tumors recorded in patients without Paget disease.

Metastases from lymphomas, prostate cancer, and breast cancer certainly occur in bone, but rarely in pagetic sites.⁴³ A recent case study noted that patients with prostate cancer who also had Paget disease had a later onset of metastasis to bone than patients without coincident Paget disease.⁴⁴

A THOUGHTFUL ASSESSMENT

Evaluating a patient with Paget disease requires a thoughtful assessment of its musculoskeletal consequences in an aging skeleton. Pain in Paget disease is often multifactorial. In the elderly, end-stage degenerative disease of the spine, hip, and knees, mechanical instability, compression fractures of the spine, and neuropathies may compound the clinical picture. Therefore, a thorough evaluation is required to plan effective therapy.

Alkaline phosphatase and other markers

A screening serum alkaline phosphatase level is usually sufficient to measure bone turnover. Produced by osteoblasts, alkaline phosphatase is a marker of bone formation, but an imperfect one. Often it is elevated in active Paget disease—but not always.⁴⁵ Many patients have normal serum alkaline phosphatase levels, particularly if they have monostotic (single-bone) disease. It is unclear why, in a disorder marked by accelerated bone remodeling, the biochemical markers are inconsistent measures of bone turnover.

Research into biochemical markers of Paget disease has had two aims: to identify the single best marker for baseline assessment of pagetic bone activity and to find out whether this measurement responds to therapy.^46,47 Measures of bone formation such as bone-specific alkaline phosphatase, osteocalcin, and the procollagen type I peptides, and measures of bone resorption including the pyridinolines, hydroxyproline, and cross-linked collagens, have been analyzed as markers of bone remodeling and show no real advantage over the serum alkaline phosphatase level as reflections of bone turnover. As alkaline phosphatase measurement is inexpensive, available, and reliable, it should be used preferentially, with gamma-glutamyl transpeptidate or 5′ nucleotidase confirming the source as either liver or bone. Readers are directed to a recent review in which the utility of these markers is explored in more detail.⁴⁸

Imaging studies

Bone scans can give us an idea of the extent, location, and general activity of the disease (Figure 3). Uptake is avid in affected bones, beginning in the subchondral region and spreading throughout the bone. Bone scans can be particularly useful in defining sites of active disease when the serum alkaline phosphatase level is normal.

Plain radiography of the affected bones outlines the anatomy of the problem and gives some insight into the cause of pain (Figure 3).

Computed tomography or magnetic resonance imaging may prove useful in cases of spinal stenosis, cauda equina syndrome, compression fractures, or suspected malignancy (Figure  4), but these studies are expensive and generally are not needed.

Radiographic features. Paget disease is presumed to be a disease of the osteoclast, and the earliest lesion is described as lytic. In my own experience, it is unusual to see a purely lytic lesion, although sometimes the disease presents in the skull in this way—osteoporosis circumscripta—or in the femur or tibia with an advancing edge of pure osteolysis.

More often, one sees evidence of both resorption by osteoclasts and formation by osteoblasts, reflecting the coupling of these two processes in this disease. Radiographic findings on plain films are usually definitive, showing enlargement of the affected bone, deformity, coarsened trabeculae, and thickened cortices with tunneling (Figure 5).⁴⁹ In weightbearing bones, pseudofractures may stud the convex surface. These incongruities of bone may persist for years, heralding fracture only when there is focal pain (Figure 6).⁵⁰

Biopsy is infrequently needed

If these diagnostic findings are not present, then biopsy is indicated. In the United Sates and Canada, where Paget disease is fairly common, biopsy is infrequently needed and is usually reserved for situations in which the differential diagnosis includes cancer, as when the cortex cannot be clearly visualized, the lesions are atypical in pattern or location, or there is a single sclerotic vertebral body on imaging.⁵¹

The other indication for biopsy is a “new” pagetic lesion. For reasons unknown, the pattern of skeletal involvement in Paget disease tends to be stable throughout the patient’s lifetime. This is another reason why a baseline bone scan is useful.

TREATMENT WITH BISPHOSPHONATES

Treatment of Paget disease today relies for the most part on the new generation of nitrogen-containing bisphosphonates. As a class, these are antiresorptive agents that inhibit osteoclasts; in this way they slow bone remodeling and enhance the deposition of normal lamellar bone. Their clinical efficacy in Paget disease, coupled with the observation that the earliest lesion in Paget disease is lytic, underscores the principle that Paget disease is a disorder of the osteoclast.

Oral bisphosphonates

Etidronate, approved in 1977, was the first bisphosphonate licensed to treat Paget disease, and it remains available for this indication in the United States. Used in 6-month regimens, it lowers the serum alkaline phosphatase level in some patients, but it has a narrow therapeutic margin. Drug-induced osteomalacia and worsening lytic lesions and fractures in weight-bearing bones are some of the complications.⁵² When the nitrogen-containing bisphosphonates were developed, they proved to be more potent antiresorptive agents that pose less risk of mineralization defects at prescribed doses.

Alendronate, approved in 1995, is an oral nitrogen-containing bisphosphonate that is effective in treating Paget disease.⁵³ Alendronate is now available in the United States only through special programs (eg, the CVS ProCare Program); the paperwork required to secure this drug is onerous, so the drug is used infrequently. Studies in Paget disease showed that it normalizes the serum alkaline phosphatase level, improves the radiographic appearance, and eases pain in many patients.⁵⁴ The dosage is 40 mg daily for 6 months.

Risedronate, approved in 1998, is another oral nitrogen-containing bisphosphonate and is comparable to alendronate in efficacy.⁵⁵ The dosage is 30 mg daily for 2 months.

Tiludronate is another oral bisphosphonate with a different mechanism of action from the nitrogen-containing bisphosphonates.⁵⁶ It is safe, often effective, but less potent than the newer agents.

The oral bisphosphonates are well tolerated, with few side effects other than gastrointestinal distress. As a class, they are poorly absorbed and so must be taken fasting with a full glass of water on rising, after which the patient should remain upright without food or drink for 30 to 60 minutes. This is a nuisance for elderly patients already on multiple medications and thus makes intravenous agents appealing.

Intravenous bisphosphonates

Pamidronate was approved in 1994. It is quite effective in many patients with Paget disease. There is no consensus around the world on dosing, with regimens ranging from 30 mg to 90 mg or more intravenously in divided doses given over 2 to 4 hours from once a day to once a week. In the United States, 30 mg is given over 4 hours on 3 consecutive days. Resistance to pamidronate has been described; the mechanism is unknown.

Zoledronic acid is a nitrogen-containing bisphosphonate. It is given as a single infusion over 15 minutes, and re-treatment may not be necessary for years. A randomized clinical trial in 2005 demonstrated the efficacy of zoledronic acid 5 mg by infusion compared with oral risedronate in the treatment of Paget disease.⁵⁷ In observational extension studies lasting as long as 6.5 years, zoledronic acid has been shown to be superior to risedronate in terms of the proportion of patients experiencing a sustained clinical remission.⁵⁸

While there are many bisphosphonates on the market, an infusion of 5 mg of zoledronic acid seems optimal in most patients who do not have a contraindication or an aversion to intravenous therapy. It tends to normalize the serum alkaline phosphatase level quickly and to leave more patients in sustained biochemical remission than do older bisphosphonates, as noted above. It also tends to be more effective in normalizing the serum alkaline phosphatase level when a patient has used other bisphosphonates in the past or has become resistant to them.

Bisphosphonates reduce bone turnover but do not correct deformities

In randomized clinical trials, bisphosphonates have been shown to restore bone remodeling to more normal levels, to ease pain from pagetic bone, to lower the serum alkaline phosphatase level, and to heal radiographic lesions, but these drugs have not been proven to prevent progression of deformity or to restore the structural integrity of bone (Figure 6).

The Paget’s Disease: Randomized Trial of Intensive Versus Symptomatic Management (PRISM), in 1,324 people with Paget disease in the United Kingdom, showed no difference in the incidence of fracture, orthopedic surgery, quality of life, or hearing thresholds over 2 to 5 years in patients treated with bisphosphonates vs those treated symptomatically, despite a significant difference in serum alkaline phosphatase in the two groups (P < .001).⁵⁹

In the observational extension study of zoledronic acid described above,⁵⁸ three of four fractures occurred in the group treated with zoledronic acid, echoing the findings of the PRISM study.

Adverse effects of bisphosphonates

The more potent the bisphosphonate is as an antiresorptive agent, the more it suppresses normal bone remodeling, which can lead to osteonecrosis of the jaw and to atypical femoral fractures.^60,61 These complications are unusual in patients with Paget disease because the treatment is intermittent. Sometimes a single dose of zoledronic acid or one course of risedronate or alendronate will last for years.

All the nitrogen-containing bisphosphonates, particularly zoledronic acid, may provoke flulike symptoms of fever, arthralgias, and bone pain. This effect is self-limited, resolves in days, and does not tend to recur. Bone pain may be more sustained, but this also passes, and within weeks the antiresorptive process has abated and pagetic bone pain will ease. Atrial fibrillation is not an anticipated complication of treatment with a bisphosphonate.⁶² The risk of esophageal cancer is not confirmed at this time.⁶³ Other rare complications of the bisphosphonates include iritis, acute renal failure, and allergy.

Bisphosphonates are not approved for use in patients with creatinine clearance less than 30 mL/min, or in pregnancy.

Other treatments

Calcitonin, an older agent, can still be useful in easing the pain of Paget disease, healing bone lesions, and reducing the metabolic activity of pagetic bone in patients who cannot receive bisphosphonates. It is given by injection in doses of 50 to 100 IU daily or every other day. Although unlikely to effect a sustained clinical remission, calcitonin remains a safe, well-tolerated, and well-studied medication in Paget disease and is approved for this indication.^64,65

Denosumab has not been formally studied in Paget disease, but a recent case report indicated it was effective.⁶⁶

A conservative strategy

Guidelines for treating Paget disease have been written at various times in many countries, including Italy (2007),⁶⁷ the United Kingdom (2004),⁶⁸ Japan (2006),⁶⁹ and Canada (2007).⁷⁰ Recommendations differ, in part because it is hard to ascertain whether long-term outcomes are improved by treatment, and in part because the prevalence of Paget disease is decreasing and its severity is lessening.^11,12 Some guidelines are outdated, since they do not include the newer bisphosphonates.

If the natural history of untreated Paget disease involves the gradual evolution over more than 20 years of bowing deformities in the lower limbs, rigidity and overgrowth of the spine, and softening and enlargement of the skull, as described by Sir James Paget, then treatment should be initiated in hopes that it will modify the outcome. We have no lens to better focus this question on the effect of treatment on the natural history of the disease. We have the PRISM study, designed before zoledronic acid was approved and only 2 to 5 years in duration. And we have the epidemiologic data demonstrating that most patients have no symptoms during their lifetime.

We see the crippling bone disease described by Sir James Paget so infrequently today in the United States that we forget the profound morbidity that may attend the skeletal changes of Paget disease that were common in the early 20th century. Once the bones of the skull are overgrown, the limbs are bowed, and the degenerative joint disease is present, no medication can reverse these changes. Then, the integrity of the bone is lost, and the vulnerability to fracture, early osteoarthritis, nerve compression syndromes, and hearing loss persist. Understanding these consequences prompts the recommendation of early treatment in patients with Paget disease, in hopes of mitigating disease progression.

Patients with active Paget disease, documented either by an elevated serum alkaline phosphatase or by a bone scan, should be treated with a bisphosphonate if the disease is found in sites where remodeling of bone may lead to complications. Such sites include the skull, spine, and long bones of the lower extremity. Paget disease of bone in the pelvis tends to give little trouble (Figure 2) unless it is proximal to a joint, when pain and early arthritis may result. Treatment is safe and, I think, prudent to undertake in any person over age 55 with active disease. To prevent hypocalcemia during treatment, all patients should be repleted with vitamin D and maintained on calcium 1,200 mg daily through diet or supplements with meals.

Throughout the evaluation and treatment, it is important to remember that pain may not emanate from pagetic bone. If medication for Paget disease proves ineffective in the first few months, analgesics, bracing, walking aids, and operative management⁷¹ are adjunctive therapies to improve the functional status of these patients.

It is a remarkable clinical observation that treatment of Paget disease may rapidly reverse neurologic syndromes, resolve the erythema or warmth overlying active pagetic bone, and diminish the risk of bleeding with surgery. This response to therapy suggests that there is prompt inhibition and apoptosis of the osteoclasts, accompanied by diminished vascularity of bone. Whatever the mechanism, it is worth treating patients who have spinal stenosis, arthritis, and nerve compression syndromes with calcitonin or bisphosphonates before surgical intervention, whenever possible.^34,72

Patients with an osteoporotic hip fracture suffer from profound morbidity and are at a heightened risk of death. It is therefore essential that they receive treatment with a bisphosphonate known to modify the subsequent risk of fracture at any site—eg, alendronate (Fosamax), risedronate (Actonel), or zoledronic acid (Reclast).

However, there is concern that starting a bisphosphonate too soon after surgery could disrupt bone remodeling and delay fracture repair.

Only one clinical study addressed the timing of bisphosphonate therapy after hip fracture repair. In this study, Eriksen et al¹ performed a post hoc analysis of data from the Health Outcomes and Reduced Incidence With Zoledronic Acid Once Yearly Recurrent Fracture Trial (HORIZON-RFT)² and concluded that the optimal time to give intravenous zoledronic acid is 2 to 12 weeks after surgical repair of the fracture.

In a frail, elderly patient with comorbidities, a single intravenous 5-mg dose of zoledronic acid guarantees adequate treatment, obviating issues of poor compliance and oral absorption and loss to follow-up. Sufficient levels of vitamin D and calcium should be ensured.

THE EVIDENCE

The original HORIZON-RFT study,² published in 2007, compared intravenous zoledronic acid against placebo in elderly patients with osteoporotic hip fracture. Most of the patients were white women; their mean age was 74; 1,065 received intravenous zoledronic acid, and 1,062 received placebo. All received vitamin D and calcium.

The trial showed a clear reduction in the rate of recurrent fractures at other sites (a primary end point) and a reduction in the rate of all-cause mortality in patients treated within 90 days of fracture. A total of 424 fractures occurred in 231 patients. The risk of any new clinical fracture was 35% lower with treatment than with placebo (occurring in 8.6% vs 13.9% of patients, P = .001), and the number of deaths due to any cause was 28% lower with treatment than with placebo (occurring in 101 vs 141, P = .01).²

The mean time to fracture was 39.8 months in the treated group vs 36.4 in the placebo group. The fracture risk reduction began to be apparent by 12 months, and the reduction in mortality rate by 16 months.²

In a post hoc analysis of the trial, Eriksen et al¹ attempted to ascertain the optimal time for therapy in terms of fracture risk and mortality reduction. Analyzing the data by 2-week intervals beginning after the surgical repair of the fracture, the authors found that only 56 patients (5.3%) had received zoledronic acid within 2 weeks of surgery and only 47 had received placebo, and they saw no advantage to intravenous zoledronic acid compared with placebo in these first 2 weeks with respect to bone mineral density, fracture risk, or risk of death. However, excluding this small subset, antifracture efficacy and reduction in mortality rate were present when patients were treated with zoledronic acid in the 2 to 12 weeks after hip fracture repair, and improvement in bone mineral density at the hip was noted at 12 months in all cohorts.

Colón-Emeric et al³ performed another post hoc analysis, attempting to explain the lower mortality rate seen in patients treated with zoledronic acid. It had been an unexpected finding, and determinants of mortality rate reduction were hampered by a limited knowledge of the true cause of death or the circumstances of care after fracture. The authors concluded that only 8% of the reduction in mortality rate evident early in the second year of treatment with zoledronic acid could be attributed to a reduction in fractures.³ Other mechanisms by which the mortality rate reduction occurred remained unclear.

Curiously, in another large randomized controlled trial of zoledronic acid, in women with postmenopausal osteoporosis, Black et al⁴ reported that more patients died in the treated group (130 of 3,862) than in the placebo group (112 of 3,852). This difference was not statistically significant, but neither was it explained.

A meta-analysis by Bolland et al⁵ examined the effect of other osteoporosis treatments on mortality rate, using randomized controlled trials that lasted more than 12 months and that reported more than 10 deaths. The authors concluded the following:

• In the trials in which bisphosphonates reduced the mortality rate, the mortality rate in the placebo group was higher than 10 per 1,000 patient-years
• The effect of osteoporosis treatment on the mortality rate in a frail, elderly population is evident using agents with proven efficacy in reducing vertebral and nonvertebral fractures, eg, alendronate, risedronate, and zoledronic acid.⁵

THE SCIENCE

Osteoporotic fractures occur with minimal trauma, with the failure of bone attributed to impaired integrity of bone microarchitecture. The ultimate goal of fracture repair is to restore bone size, shape, and tissue properties. The issue of when to treat with a bisphosphonate after hip fracture arises because bisphosphonates are known to disrupt bone remodeling and so delay fracture repair.

After fracture, both anabolic and catabolic phases occur.⁶ The final outcome depends on the following:

• The type of intervention to stabilize the fracture site (eg, surgical repair)
• The inflammatory cytokines and growth factors released by the cellular elements in bloody and disrupted tissue.

Oxygen tension, angiogenesis, and osteoblasts are critical to primary bone formation, and osteoclasts are essential in remodeling this initial bone deposition. These late phases of fracture repair are most vulnerable to the bisphosphonates, through suppression of osteoclast resorption and possibly through decreased angiogenesis.⁶ Callus formation is sustained, but bone remodeling is delayed.

Amanat et al⁷ examined the timing of a single dose of zoledronic acid after fracture repair in a rat model of diaphyseal fracture and found that the callus was larger and stronger if the bisphosphonate dose had been delayed 1 or 2 weeks. The animals treated with zoledronic acid showed a remarkable trabecular network of bone between the original femoral cortex and the new cortical bone that was not present in the control group, perhaps contributing to the enhanced mechanical properties of the callus. Other studies suggest single dosing rather than continuous dosing may be advantageous in fracture healing.⁸

THE REALITY

Healthy dogs or growing rats with linear diaphyseal fractures are imperfect models for elderly osteoporotic patients with hip fracture, as Dr. Herbert Fleisch noted in his editorial, “Can bisphosphonates be given to patients with fractures?”⁹ Still, if retained primary bone can be used in the process of fracture repair to gain an early mechanical advantage, then perhaps delayed remodeling will permit early mobilization and further fracture prevention in humans.

How soon after hip fracture surgery should a patient start a bisphosphonate? The only data we have are from a single randomized controlled trial designed to measure fracture risk reduction in osteoporotic patients with hip fracture using intravenous zoledronic acid 5 mg compared with placebo.² A post hoc analysis of this study¹ generated the limited clinical data we have on the optimal timing of the treatment. Linking these study data with the laboratory data, one would intuit that delaying the infusion of zoledronic acid for at least 2 weeks after hip fracture repair would offer a clinical reduction in fracture risk and improvement (or stabilization) in bone mineral density by 12 months, and a reduction in the rate of all-cause mortality beginning at 16 months.

Patients with an osteoporotic hip fracture suffer from profound morbidity and are at a heightened risk of death. It is therefore essential that they receive treatment with a bisphosphonate known to modify the subsequent risk of fracture at any site—eg, alendronate (Fosamax), risedronate (Actonel), or zoledronic acid (Reclast).

However, there is concern that starting a bisphosphonate too soon after surgery could disrupt bone remodeling and delay fracture repair.

Only one clinical study addressed the timing of bisphosphonate therapy after hip fracture repair. In this study, Eriksen et al¹ performed a post hoc analysis of data from the Health Outcomes and Reduced Incidence With Zoledronic Acid Once Yearly Recurrent Fracture Trial (HORIZON-RFT)² and concluded that the optimal time to give intravenous zoledronic acid is 2 to 12 weeks after surgical repair of the fracture.

In a frail, elderly patient with comorbidities, a single intravenous 5-mg dose of zoledronic acid guarantees adequate treatment, obviating issues of poor compliance and oral absorption and loss to follow-up. Sufficient levels of vitamin D and calcium should be ensured.

THE EVIDENCE

The original HORIZON-RFT study,² published in 2007, compared intravenous zoledronic acid against placebo in elderly patients with osteoporotic hip fracture. Most of the patients were white women; their mean age was 74; 1,065 received intravenous zoledronic acid, and 1,062 received placebo. All received vitamin D and calcium.

The trial showed a clear reduction in the rate of recurrent fractures at other sites (a primary end point) and a reduction in the rate of all-cause mortality in patients treated within 90 days of fracture. A total of 424 fractures occurred in 231 patients. The risk of any new clinical fracture was 35% lower with treatment than with placebo (occurring in 8.6% vs 13.9% of patients, P = .001), and the number of deaths due to any cause was 28% lower with treatment than with placebo (occurring in 101 vs 141, P = .01).²

The mean time to fracture was 39.8 months in the treated group vs 36.4 in the placebo group. The fracture risk reduction began to be apparent by 12 months, and the reduction in mortality rate by 16 months.²

In a post hoc analysis of the trial, Eriksen et al¹ attempted to ascertain the optimal time for therapy in terms of fracture risk and mortality reduction. Analyzing the data by 2-week intervals beginning after the surgical repair of the fracture, the authors found that only 56 patients (5.3%) had received zoledronic acid within 2 weeks of surgery and only 47 had received placebo, and they saw no advantage to intravenous zoledronic acid compared with placebo in these first 2 weeks with respect to bone mineral density, fracture risk, or risk of death. However, excluding this small subset, antifracture efficacy and reduction in mortality rate were present when patients were treated with zoledronic acid in the 2 to 12 weeks after hip fracture repair, and improvement in bone mineral density at the hip was noted at 12 months in all cohorts.

Colón-Emeric et al³ performed another post hoc analysis, attempting to explain the lower mortality rate seen in patients treated with zoledronic acid. It had been an unexpected finding, and determinants of mortality rate reduction were hampered by a limited knowledge of the true cause of death or the circumstances of care after fracture. The authors concluded that only 8% of the reduction in mortality rate evident early in the second year of treatment with zoledronic acid could be attributed to a reduction in fractures.³ Other mechanisms by which the mortality rate reduction occurred remained unclear.

Curiously, in another large randomized controlled trial of zoledronic acid, in women with postmenopausal osteoporosis, Black et al⁴ reported that more patients died in the treated group (130 of 3,862) than in the placebo group (112 of 3,852). This difference was not statistically significant, but neither was it explained.

A meta-analysis by Bolland et al⁵ examined the effect of other osteoporosis treatments on mortality rate, using randomized controlled trials that lasted more than 12 months and that reported more than 10 deaths. The authors concluded the following:

• In the trials in which bisphosphonates reduced the mortality rate, the mortality rate in the placebo group was higher than 10 per 1,000 patient-years
• The effect of osteoporosis treatment on the mortality rate in a frail, elderly population is evident using agents with proven efficacy in reducing vertebral and nonvertebral fractures, eg, alendronate, risedronate, and zoledronic acid.⁵

THE SCIENCE

Osteoporotic fractures occur with minimal trauma, with the failure of bone attributed to impaired integrity of bone microarchitecture. The ultimate goal of fracture repair is to restore bone size, shape, and tissue properties. The issue of when to treat with a bisphosphonate after hip fracture arises because bisphosphonates are known to disrupt bone remodeling and so delay fracture repair.

After fracture, both anabolic and catabolic phases occur.⁶ The final outcome depends on the following:

• The type of intervention to stabilize the fracture site (eg, surgical repair)
• The inflammatory cytokines and growth factors released by the cellular elements in bloody and disrupted tissue.

Oxygen tension, angiogenesis, and osteoblasts are critical to primary bone formation, and osteoclasts are essential in remodeling this initial bone deposition. These late phases of fracture repair are most vulnerable to the bisphosphonates, through suppression of osteoclast resorption and possibly through decreased angiogenesis.⁶ Callus formation is sustained, but bone remodeling is delayed.

Amanat et al⁷ examined the timing of a single dose of zoledronic acid after fracture repair in a rat model of diaphyseal fracture and found that the callus was larger and stronger if the bisphosphonate dose had been delayed 1 or 2 weeks. The animals treated with zoledronic acid showed a remarkable trabecular network of bone between the original femoral cortex and the new cortical bone that was not present in the control group, perhaps contributing to the enhanced mechanical properties of the callus. Other studies suggest single dosing rather than continuous dosing may be advantageous in fracture healing.⁸

THE REALITY

Healthy dogs or growing rats with linear diaphyseal fractures are imperfect models for elderly osteoporotic patients with hip fracture, as Dr. Herbert Fleisch noted in his editorial, “Can bisphosphonates be given to patients with fractures?”⁹ Still, if retained primary bone can be used in the process of fracture repair to gain an early mechanical advantage, then perhaps delayed remodeling will permit early mobilization and further fracture prevention in humans.

How soon after hip fracture surgery should a patient start a bisphosphonate? The only data we have are from a single randomized controlled trial designed to measure fracture risk reduction in osteoporotic patients with hip fracture using intravenous zoledronic acid 5 mg compared with placebo.² A post hoc analysis of this study¹ generated the limited clinical data we have on the optimal timing of the treatment. Linking these study data with the laboratory data, one would intuit that delaying the infusion of zoledronic acid for at least 2 weeks after hip fracture repair would offer a clinical reduction in fracture risk and improvement (or stabilization) in bone mineral density by 12 months, and a reduction in the rate of all-cause mortality beginning at 16 months.

Patients with an osteoporotic hip fracture suffer from profound morbidity and are at a heightened risk of death. It is therefore essential that they receive treatment with a bisphosphonate known to modify the subsequent risk of fracture at any site—eg, alendronate (Fosamax), risedronate (Actonel), or zoledronic acid (Reclast).

However, there is concern that starting a bisphosphonate too soon after surgery could disrupt bone remodeling and delay fracture repair.

Only one clinical study addressed the timing of bisphosphonate therapy after hip fracture repair. In this study, Eriksen et al¹ performed a post hoc analysis of data from the Health Outcomes and Reduced Incidence With Zoledronic Acid Once Yearly Recurrent Fracture Trial (HORIZON-RFT)² and concluded that the optimal time to give intravenous zoledronic acid is 2 to 12 weeks after surgical repair of the fracture.

In a frail, elderly patient with comorbidities, a single intravenous 5-mg dose of zoledronic acid guarantees adequate treatment, obviating issues of poor compliance and oral absorption and loss to follow-up. Sufficient levels of vitamin D and calcium should be ensured.

THE EVIDENCE

The original HORIZON-RFT study,² published in 2007, compared intravenous zoledronic acid against placebo in elderly patients with osteoporotic hip fracture. Most of the patients were white women; their mean age was 74; 1,065 received intravenous zoledronic acid, and 1,062 received placebo. All received vitamin D and calcium.

The trial showed a clear reduction in the rate of recurrent fractures at other sites (a primary end point) and a reduction in the rate of all-cause mortality in patients treated within 90 days of fracture. A total of 424 fractures occurred in 231 patients. The risk of any new clinical fracture was 35% lower with treatment than with placebo (occurring in 8.6% vs 13.9% of patients, P = .001), and the number of deaths due to any cause was 28% lower with treatment than with placebo (occurring in 101 vs 141, P = .01).²

The mean time to fracture was 39.8 months in the treated group vs 36.4 in the placebo group. The fracture risk reduction began to be apparent by 12 months, and the reduction in mortality rate by 16 months.²

In a post hoc analysis of the trial, Eriksen et al¹ attempted to ascertain the optimal time for therapy in terms of fracture risk and mortality reduction. Analyzing the data by 2-week intervals beginning after the surgical repair of the fracture, the authors found that only 56 patients (5.3%) had received zoledronic acid within 2 weeks of surgery and only 47 had received placebo, and they saw no advantage to intravenous zoledronic acid compared with placebo in these first 2 weeks with respect to bone mineral density, fracture risk, or risk of death. However, excluding this small subset, antifracture efficacy and reduction in mortality rate were present when patients were treated with zoledronic acid in the 2 to 12 weeks after hip fracture repair, and improvement in bone mineral density at the hip was noted at 12 months in all cohorts.

Colón-Emeric et al³ performed another post hoc analysis, attempting to explain the lower mortality rate seen in patients treated with zoledronic acid. It had been an unexpected finding, and determinants of mortality rate reduction were hampered by a limited knowledge of the true cause of death or the circumstances of care after fracture. The authors concluded that only 8% of the reduction in mortality rate evident early in the second year of treatment with zoledronic acid could be attributed to a reduction in fractures.³ Other mechanisms by which the mortality rate reduction occurred remained unclear.

Curiously, in another large randomized controlled trial of zoledronic acid, in women with postmenopausal osteoporosis, Black et al⁴ reported that more patients died in the treated group (130 of 3,862) than in the placebo group (112 of 3,852). This difference was not statistically significant, but neither was it explained.

A meta-analysis by Bolland et al⁵ examined the effect of other osteoporosis treatments on mortality rate, using randomized controlled trials that lasted more than 12 months and that reported more than 10 deaths. The authors concluded the following:

• In the trials in which bisphosphonates reduced the mortality rate, the mortality rate in the placebo group was higher than 10 per 1,000 patient-years
• The effect of osteoporosis treatment on the mortality rate in a frail, elderly population is evident using agents with proven efficacy in reducing vertebral and nonvertebral fractures, eg, alendronate, risedronate, and zoledronic acid.⁵

THE SCIENCE

Osteoporotic fractures occur with minimal trauma, with the failure of bone attributed to impaired integrity of bone microarchitecture. The ultimate goal of fracture repair is to restore bone size, shape, and tissue properties. The issue of when to treat with a bisphosphonate after hip fracture arises because bisphosphonates are known to disrupt bone remodeling and so delay fracture repair.

After fracture, both anabolic and catabolic phases occur.⁶ The final outcome depends on the following:

• The type of intervention to stabilize the fracture site (eg, surgical repair)
• The inflammatory cytokines and growth factors released by the cellular elements in bloody and disrupted tissue.

Oxygen tension, angiogenesis, and osteoblasts are critical to primary bone formation, and osteoclasts are essential in remodeling this initial bone deposition. These late phases of fracture repair are most vulnerable to the bisphosphonates, through suppression of osteoclast resorption and possibly through decreased angiogenesis.⁶ Callus formation is sustained, but bone remodeling is delayed.

Amanat et al⁷ examined the timing of a single dose of zoledronic acid after fracture repair in a rat model of diaphyseal fracture and found that the callus was larger and stronger if the bisphosphonate dose had been delayed 1 or 2 weeks. The animals treated with zoledronic acid showed a remarkable trabecular network of bone between the original femoral cortex and the new cortical bone that was not present in the control group, perhaps contributing to the enhanced mechanical properties of the callus. Other studies suggest single dosing rather than continuous dosing may be advantageous in fracture healing.⁸

THE REALITY

Healthy dogs or growing rats with linear diaphyseal fractures are imperfect models for elderly osteoporotic patients with hip fracture, as Dr. Herbert Fleisch noted in his editorial, “Can bisphosphonates be given to patients with fractures?”⁹ Still, if retained primary bone can be used in the process of fracture repair to gain an early mechanical advantage, then perhaps delayed remodeling will permit early mobilization and further fracture prevention in humans.

How soon after hip fracture surgery should a patient start a bisphosphonate? The only data we have are from a single randomized controlled trial designed to measure fracture risk reduction in osteoporotic patients with hip fracture using intravenous zoledronic acid 5 mg compared with placebo.² A post hoc analysis of this study¹ generated the limited clinical data we have on the optimal timing of the treatment. Linking these study data with the laboratory data, one would intuit that delaying the infusion of zoledronic acid for at least 2 weeks after hip fracture repair would offer a clinical reduction in fracture risk and improvement (or stabilization) in bone mineral density by 12 months, and a reduction in the rate of all-cause mortality beginning at 16 months.