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Classification and evaluation of myoclonus

John N Caviness, MD
Section Editor
Howard I Hurtig, MD
Deputy Editor
John F Dashe, MD, PhD


Myoclonus is a clinical sign that is characterized by brief, shock-like, involuntary movements caused by muscular contractions or inhibitions [1]. Muscular contractions produce positive myoclonus, whereas muscular inhibitions produce negative myoclonus (ie, asterixis). Patients will usually describe myoclonus as consisting of "jerks," "shakes," or "spasms."

Myoclonic movements have many possible etiologies, anatomic sources, and pathophysiologic features [2]. Myoclonus may be classified by clinical presentation, examination findings, clinical neurophysiology testing, and etiology.

This topic will review the classification and evaluation of myoclonus. Treatment is discussed separately. (See "Treatment of myoclonus".)


In addition to the clinical and etiologic classification discussed below, myoclonus can be classified by the localization of the physiologic mechanism that generates it (table 1). These anatomic-physiologic categories are as follows:


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Literature review current through: Nov 2017. | This topic last updated: Sep 27, 2017.
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