Functional movement disorders (FMDs) are clinical syndromes defined by the occurrence of abnormal involuntary movements that are incongruent with a known neurological cause and are significantly improved on neurological exam with distraction or non-physiologic maneuvers. This definition replaces the previous one that considered FMDs to be “psychogenic movement disorders” and attributed the occurrence of the abnormal movements to a psychiatric cause. FMDs were first described in the late 19th and early 20th centuries and have been the subject of great interest and puzzlement ever since.
In addition to “psychogenic,” alternative terms for FMDs include “hysterical” or “nonorganic” movement disorders and “medically unexplained” motor symptoms. In modern times, awareness of FMDs has increased in the movement disorder literature.
However, the pathogenesis and pathophysiology of FMDs are not fully understood, and debate continues as to whether “functional” or “psychogenic” is the better term for these movement disorders
The dangers of FMDs are manifold: excessive, unnecessary, and costly investigations of FMD resulting in reinforcing the sick role, misdiagnosing organic illness as psychogenic misdiagnosing FMD as organic, and failure to recognise a kernel of organic illness embedded in the symptoms of an FMD. The prevalence, poor prognosis, and intensive health care utilisation of FMDs present a problem that has been likened to a crisis in neurology. In order to offer the best chance for remission and to use scarce resources wisely, rapid and accurate diagnosis of FMDs is essential.
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