Diagnosis of myoclonus in adults.

Myoclonus, defined as shock-like involuntary movement, may be physiological or caused by a very wide variety of hereditary and acquired conditions. Be cause myoclonus can originate from different disorders and lesions affectin g quite varied levels of the central and peripheral nervous systems, it rep resents from many points of view a diagnostic challenge, Moreover, new enti ties have been recently individualized, such as cortical tremor, which dese rve renewed attention. The aim of this review is to propose a rationale for a diagnostic approach based on clinical and electrophysiological grounds. In this setting, we successively address 1) the clinical features allowing a positive diagnosis of myoclonus; 2) the clinical clues to the etiology; 3 ) the relevance of the clinical context to the diagnosis; and 4) the contri bution of neurophysiology. Differentiating myoclonus from ties, spasm, chor ea and dystonia can be difficult, and a careful reappraisal of clinical fea tures allowing precise identification is presented. Moreover, the topograph ical distribution of myoclonus, the temporal pattern of muscle recruitment, the condition of occurrence and the rhythm of the event, may provide clini cal clues relevant to the diagnosis. Myoclonus without associated epilepsy, myoclonus with epilepsy, myoclonus with encephalopathy, parkinsonism and/o r dementia represent overlapping clinical categories, although they remain useful for the diagnostic approach. Using electrophysiology (including back -averaging EEG, MEG, SEP, C-reflex studies) to determine the origin of myoc lonus may not allow us to focus on the underlying condition. Indeed, in man y instances, the myoclonus is cortical in origin, but the pathology is foun d elsewhere, (C) 2001 Editions scientifiques et medicales Elsevier SAS.