Myoclonus

Abstract Myoclonus is characterized by quick involuntary jerks and is classified as one of the hyperkinetic movement disorders. Myoclonus can be caused by muscle contractions (positive myoclonus) or by interruptions of tonic muscle (negative myoclonus). The main classification of myoclonus is based on the anatomical origin of the myoclonic jerks: cortical, subcortical, spinal, and peripheral myoclonus, each with distinctive physiological mechanisms. Clinical characteristics, aetiology, and treatment options are related to the anatomical classification of myoclonus. The epidemiology of myoclonus is poorly documented, as myoclonus has many different causes and a spectrum of clinical presentations. A single study showed a lifetime prevalence of 8.6 cases per 100 000. The aetiology of myoclonus is diverse and in 70 per cent of cases is symptomatic. Over the last 10 years new genes have been discovered for several myoclonic disorders. Recent pathophysiological studies illustrate an important role for the cerebellum in generating both cortical and subcortical myoclonus, but further studies addressing the precise mechanism of myoclonus are required. Therapy is usually symptomatic, as treatment of an underlying cause is often impossible or ineffective. Therapeutic options are mainly based on a low level of evidence as randomized controlled trials are not available.