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Five patients who presented with stimulus-induced jerking as part of an apparent myoclonic or pathological startle syndrome are reported. Neurophysiological observations in these patients suggested the jerks were voluntary in origin. These included (a) variable latencies to the onset of stimulus induced jerks, (b) latencies were greater than that seen in reflex myoclonus of cortical or brainstem origin, and were (c) longer than the fastest voluntary reaction times of normal subjects, (d) variable patterns of muscle recruitment within each jerk and, (e) significant habituation with repeated stimulation. It is argued that these features are consistent with a voluntary origin for the jerks and enable them to be distinguished from the stereotyped electrophysiological characteristics of myoclonus of cortical and brainstem origin. Electrophysiological recordings may help identify patients with this form of psychogenic movement disorder.

Original publication

DOI

10.1002/mds.870070312

Type

Journal

Mov Disord

Publication Date

1992

Volume

7

Pages

257 - 262

Keywords

Adult, Female, Humans, Male, Malingering, Muscles, Myoclonus, Neurologic Examination, Reaction Time, Reference Values, Reflex, Reflex, Startle, Somatoform Disorders