, according to new findings derived from the 2017 Global Burden of Disease study.
The authors of the analysis, led by Valery Feigin, MD, PhD, of New Zealand’s National Institute for Stroke and Applied Neurosciences, and published in the February 2021 issue of JAMA Neurology, looked at prevalence, incidence, mortality, and disability-adjusted life years for 14 neurological disorders across 50 states between 1990 and 2017. The diseases included in the analysis were stroke, Alzheimer’s disease and other dementias, Parkinson’s disease, epilepsy, multiple sclerosis, motor neuron disease, headaches, traumatic brain injury, spinal cord injuries, brain and other nervous system cancers, meningitis, encephalitis, and tetanus.
Tracking the burden of neurologic diseases
Dr. Feigin and colleagues estimated that a full 60% of the U.S. population lives with one or more of these disorders, a figure much greater than previous estimates for neurological disease burden nationwide. Tension-type headache and migraine were the most prevalent in the analysis by Dr. Feigin and colleagues. During the study period, they found, prevalence, incidence, and disability burden of nearly all the included disorders increased, with the exception of brain and spinal cord injuries, meningitis, and encephalitis.
The researchers attributed most of the rise in noncommunicable neurological diseases to population aging. An age-standardized analysis found trends for stroke and Alzheimer’s disease and other dementias to be declining or flat. Age-standardized stroke incidence dropped by 16% from 1990 to 2017, while stroke mortality declined by nearly a third, and stroke disability by a quarter. Age-standardized incidence of Alzheimer’s disease and other dementias dropped by 12%, and their prevalence by 13%, during the study period, though dementia mortality and disability were seen increasing.
The authors surmised that the age-standardized declines in stroke and dementias could reflect that “primary prevention of these disorders are beginning to show an influence.” With dementia, which is linked to cognitive reserve and education, “improving educational levels of cohort reaching the age groups at greatest risk of disease may also be contributing to a modest decline over time,” Dr. Feigin and his colleagues wrote.
Parkinson’s disease and multiple sclerosis, meanwhile, were both seen rising in incidence, prevalence, and disability adjusted life years (DALYs) even with age-standardized figures. The United States saw comparatively more disability in 2017 from dementias, Parkinson’s disease, epilepsy, multiple sclerosis, motor neuron disease, and headache disorders, which together comprised 6.7% of DALYs, compared with 4.4% globally; these also accounted for a higher share of mortality in the U.S. than worldwide. The authors attributed at least some of the difference to better case ascertainment in the U.S.
The researchers also reported variations in disease burden by state and region. While previous studies have identified a “stroke belt” concentrated in North Carolina, South Carolina, and Georgia, the new findings point to stroke disability highest in Alabama, Arkansas, and Mississippi, and mortality highest in Alabama, Mississippi, and South Carolina. The researchers noted increases in dementia mortality in these states, “likely attributable to the reciprocal association between stroke and dementia.”
Northern states saw higher burdens of multiple sclerosis compared with the rest of the country, while eastern states had higher rates of Parkinson’s disease.
Such regional and state-by state variations, Dr. Feigin and colleagues wrote in their analysis, “may be associated with differences in the case ascertainment, as well as access to health care; racial/ethnic, genetic, and socioeconomic diversity; quality and comprehensiveness of preventive strategies; and risk factor distribution.”
The researchers noted as a limitation of their study that the 14 diseases captured were not an exhaustive list of neurological conditions; chronic lower back pain, a condition included in a previous major study of the burden of neurological disease in the United States, was omitted, as were restless legs syndrome and peripheral neuropathy. The researchers cited changes to coding practice in the U.S. and accuracy of medical claims data as potential limitations of their analysis. The Global Burden of Disease study is funded by the Bill and Melinda Gates Foundation, and several of Dr. Feigin’s coauthors reported financial relationships with industry.
Time to adjust the stroke belt?
Amelia Boehme, PhD, a stroke epidemiologist at Columbia University Mailman School of Public Health in New York, said in an interview that the current study added to recent findings showing surprising local variability in stroke prevalence, incidence, and mortality. “What we had always conceptually thought of as the ‘stroke belt’ isn’t necessarily the case,” Dr. Boehme said, but is rather subject to local, county-by-county variations. “Looking at the data here in conjunction with what previous authors have found, it raises some questions as to whether or not state-level data is giving a completely accurate picture, and whether we need to start looking at the county level and adjust for populations and age.” Importantly, Dr. Boehme said, data collected in the Global Burden of Disease study tends to be exceptionally rigorous and systematic, adding weight to Dr. Feigin and colleagues’ suggestions that prevention efforts may be making a dent in stroke and dementia.
“More data is always needed before we start to say we’re seeing things change,” Dr. Boehme noted. “But any glimmer of optimism is welcome, especially with regard to interventions that have been put in place, to allow us to build on those interventions.”
Dr. Boehme disclosed no financial conflicts of interest.