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Comment & Response
December 10, 2018

The Wide Spectrum of Functional Movement Disorders

Author Affiliations
  • 1Parkinson's Disease Center and Movement Disorders Clinic, Department of Neurology, Baylor College of Medicine, Houston, Texas
  • 2University of Guanajuato, Guanajuato, México
JAMA Neurol. Published online December 10, 2018. doi:10.1001/jamaneurol.2018.3905

To the Editor Functional movement disorders (FMDs) have a diverse phenomenology that may resemble “organic” movement disorders and the 2 types of movement disorders may coexist in some cases. In the review by Espay and colleagues,1 the authors discuss some of the common FMDs and other functional neurological disorders. We would like to draw attention to other common FMDs that may be encountered by general neurologists and present a diagnostic challenge. One of the most common forms of FMD is asymmetric or unilateral facial contractions that may resemble a hemifacial spasm. In contrast to organic hemifacial spasms, those of a functional (psychogenic) etiology are usually more sustained rather than clonic, distractible, and inconsistent in their location (often alternating from side to side) and phenomenology.2 Other functional facial movements, which are often misdiagnosed as tics or tardive dyskinesia, are functional stereotypies. In contrast to organic stereotypies, the functional orofacial stereotypies typically start suddenly as bizarre mouth, tongue, and jaw movements without self-biting; they are distractible and have periods of unexplained remission, features that are incongruous with drug-induced dyskinesia.3 Many patients with FMDs also have various speech and voice disorders. In one of our studies we found stuttering as the most common speech abnormality, followed by speech arrests, foreign accent syndrome, hypophonia, and dysphonia.4 Besides distractibility, periods of unexplained worsening or improvement, and prominent suggestibility, FMDs may fluctuate in response to different stimuli, including visual, auditory, and tactile inputs.5 A vibratory stimulus applied with a tuning fork along with a brief statement associated with its potential effect may be helpful to observe the movements and better appreciate its phenomenology in the clinic in patients with episodic or paroxysmal FMDs.1 This maneuver may not only help define the movement disorder but also helps the patient understand the nature of the disorder with potential therapeutic implications. Advances in clinical phenomenology, pathophysiology, and therapeutic options in patients with FMDs are redefining this complex and important field in neurology.