Revisions Needed to Streamline PMD Diagnostic Criteria

WASHINGTON — Psychogenic movement disorders could be classified with greater simplicity and possibly diagnosed with greater accuracy in a system that expands the ways in which patients can meet criteria for the disorders, according to Dr. Anthony E. Lang.

The original classification scheme for psychogenic movement disorders (PMDs) proposed by Dr. Stanley Fahn and Dr. Daniel Williams (Adv. Neurol. 1988;50:431-55) subdivided the diagnosis based on the level of diagnostic certainty. The original two categories of “documented” and “clinically established” later merged to become clinically definite PMD (Adv. Neurol. 1995;65:231-57), which are “the majority that we see in the clinics,” said Dr. Lang, professor of neurology at the University of Toronto. Other cases were classified as “probable” or “possible.”

But the Fahn and Williams classification scheme does not take into account the ability to confirm the diagnosis as psychogenic using electrophysiologic testing, Dr. Lang said at an international conference sponsored by the Movement Disorder Society.

Dr. Lang proposed revising the classification scheme to define “clinically definite” PMD as documented, clinically established plus other features (false neurologic signs or psychiatric problems), or clinically established without other features. A “laboratory-supported” definite PMD diagnosis would be made on evidence from electrophysiologic testing. “Possible” PMD could define a movement disorder that has either clinical or electrophysiologic characteristics that are suggestive of a psychogenic condition but leave room for doubt, such as patients with combined psychogenic and organic movement disorders or with organic movement disorders that have superimposed psychogenic features.

The Fahn and Williams classification system, which is the one most commonly used in research and clinical practice, also cannot accurately classify patients who have clinically unequivocal psychogenic features based on distractibility or entrainment but lack false neurologic signs or multiple somatizations that are required for a clinically established PMD diagnosis; they can only be diagnosed as probable although they meet all the clinical criteria for a “nonorganic” movement disorder, he said.

The classification system insists that probable or possible PMD can be diagnosed with patients who have movement disorders that are consistent and congruent with an organic counterpart, but many of those patients may have an organic movement disorder with a great deal of functional overlay or a combination of organic and nonorganic movement disorders, Dr. Lang said.

“It's very common to see patients with mixed [movements]. They may have some bizarre movement disorder or a phenotype that's difficult to classify but then also have a prominent tremor or dystonia,” he said.

“Certain clinical phenotypes strongly suggest a PMD, although this is a somewhat controversial area, Dr. Lang said. These include tremors that never vary in amplitude in rest, postural, and action states and certain types of leg tremor, such as prominent thigh tremors.

In addition, certain dystonic postures are characteristic of PMDs. A lack of arm swing in a patient with hemiparkinsonism may be characteristic of a PMD.

A revision of the Fahn and Williams scheme might lead to more precise diagnoses of PMDs. DR. LANG

WASHINGTON — Psychogenic movement disorders could be classified with greater simplicity and possibly diagnosed with greater accuracy in a system that expands the ways in which patients can meet criteria for the disorders, according to Dr. Anthony E. Lang.

The original classification scheme for psychogenic movement disorders (PMDs) proposed by Dr. Stanley Fahn and Dr. Daniel Williams (Adv. Neurol. 1988;50:431-55) subdivided the diagnosis based on the level of diagnostic certainty. The original two categories of “documented” and “clinically established” later merged to become clinically definite PMD (Adv. Neurol. 1995;65:231-57), which are “the majority that we see in the clinics,” said Dr. Lang, professor of neurology at the University of Toronto. Other cases were classified as “probable” or “possible.”

But the Fahn and Williams classification scheme does not take into account the ability to confirm the diagnosis as psychogenic using electrophysiologic testing, Dr. Lang said at an international conference sponsored by the Movement Disorder Society.

Dr. Lang proposed revising the classification scheme to define “clinically definite” PMD as documented, clinically established plus other features (false neurologic signs or psychiatric problems), or clinically established without other features. A “laboratory-supported” definite PMD diagnosis would be made on evidence from electrophysiologic testing. “Possible” PMD could define a movement disorder that has either clinical or electrophysiologic characteristics that are suggestive of a psychogenic condition but leave room for doubt, such as patients with combined psychogenic and organic movement disorders or with organic movement disorders that have superimposed psychogenic features.

The Fahn and Williams classification system, which is the one most commonly used in research and clinical practice, also cannot accurately classify patients who have clinically unequivocal psychogenic features based on distractibility or entrainment but lack false neurologic signs or multiple somatizations that are required for a clinically established PMD diagnosis; they can only be diagnosed as probable although they meet all the clinical criteria for a “nonorganic” movement disorder, he said.

The classification system insists that probable or possible PMD can be diagnosed with patients who have movement disorders that are consistent and congruent with an organic counterpart, but many of those patients may have an organic movement disorder with a great deal of functional overlay or a combination of organic and nonorganic movement disorders, Dr. Lang said.

“It's very common to see patients with mixed [movements]. They may have some bizarre movement disorder or a phenotype that's difficult to classify but then also have a prominent tremor or dystonia,” he said.

“Certain clinical phenotypes strongly suggest a PMD, although this is a somewhat controversial area, Dr. Lang said. These include tremors that never vary in amplitude in rest, postural, and action states and certain types of leg tremor, such as prominent thigh tremors.

In addition, certain dystonic postures are characteristic of PMDs. A lack of arm swing in a patient with hemiparkinsonism may be characteristic of a PMD.

A revision of the Fahn and Williams scheme might lead to more precise diagnoses of PMDs. DR. LANG

WASHINGTON — Psychogenic movement disorders could be classified with greater simplicity and possibly diagnosed with greater accuracy in a system that expands the ways in which patients can meet criteria for the disorders, according to Dr. Anthony E. Lang.

The original classification scheme for psychogenic movement disorders (PMDs) proposed by Dr. Stanley Fahn and Dr. Daniel Williams (Adv. Neurol. 1988;50:431-55) subdivided the diagnosis based on the level of diagnostic certainty. The original two categories of “documented” and “clinically established” later merged to become clinically definite PMD (Adv. Neurol. 1995;65:231-57), which are “the majority that we see in the clinics,” said Dr. Lang, professor of neurology at the University of Toronto. Other cases were classified as “probable” or “possible.”

But the Fahn and Williams classification scheme does not take into account the ability to confirm the diagnosis as psychogenic using electrophysiologic testing, Dr. Lang said at an international conference sponsored by the Movement Disorder Society.

Dr. Lang proposed revising the classification scheme to define “clinically definite” PMD as documented, clinically established plus other features (false neurologic signs or psychiatric problems), or clinically established without other features. A “laboratory-supported” definite PMD diagnosis would be made on evidence from electrophysiologic testing. “Possible” PMD could define a movement disorder that has either clinical or electrophysiologic characteristics that are suggestive of a psychogenic condition but leave room for doubt, such as patients with combined psychogenic and organic movement disorders or with organic movement disorders that have superimposed psychogenic features.

The Fahn and Williams classification system, which is the one most commonly used in research and clinical practice, also cannot accurately classify patients who have clinically unequivocal psychogenic features based on distractibility or entrainment but lack false neurologic signs or multiple somatizations that are required for a clinically established PMD diagnosis; they can only be diagnosed as probable although they meet all the clinical criteria for a “nonorganic” movement disorder, he said.

The classification system insists that probable or possible PMD can be diagnosed with patients who have movement disorders that are consistent and congruent with an organic counterpart, but many of those patients may have an organic movement disorder with a great deal of functional overlay or a combination of organic and nonorganic movement disorders, Dr. Lang said.

“It's very common to see patients with mixed [movements]. They may have some bizarre movement disorder or a phenotype that's difficult to classify but then also have a prominent tremor or dystonia,” he said.

“Certain clinical phenotypes strongly suggest a PMD, although this is a somewhat controversial area, Dr. Lang said. These include tremors that never vary in amplitude in rest, postural, and action states and certain types of leg tremor, such as prominent thigh tremors.

In addition, certain dystonic postures are characteristic of PMDs. A lack of arm swing in a patient with hemiparkinsonism may be characteristic of a PMD.

A revision of the Fahn and Williams scheme might lead to more precise diagnoses of PMDs. DR. LANG