Myoclonus

Myoclonus is characterised by an involuntary sudden, brief and jerky movement caused by an abrupt muscle contraction. Usually, the generator of myoclonus is localised in the central nervous system. Clinical features and neurophysiological findings for different types of myoclonus are important to point out the anatomic level of myoclonus generation, which can be cortical, subcortical, reticular and spinal. Myoclonus can also be grouped by phenomenology with a focal, multifocal, segmental or generalised distribution. The pattern of myoclonic muscle activation yields clinical information on the type of myoclonus. Myoclonus is a symptom of various neurological disorders, but can also occur in metabolic disturbances, storage diseases and toxicities. Hence, with regard to these heterogeneous aetiologies of myoclonus, its pathophysiology is in part speculative and has to be further elucidated. In clinical practice myoclonus is rather a symptom, and disorders that constitute mainly of myoclonus are rare. Myoclonus can be classified into four aetiological categories: physiological, essential, epileptic, and symptomatic. Symptomatic myoclonus is by far the most common form of myoclonus and is caused most often by post-hypoxic encephalopathies, metabolic disturbances, and infectious encephalopathies. Neurodegenerative disorders and storage diseases are less frequent causes of symptomatic myoclonus. Treatment of myoclonus is more effective in cortical than in non-cortical forms of myoclonus and consists mainly of anticonvulsants. The most effective medications used to treat cortical myoclonus are clonazepam, valproic acid, and piracetam. Post-hypoxic myoclonus can be relieved by 5-HTP and levetiracetam. However, evidence of myoclonus treatment is based mainly on case series with only a few controlled studies. This review focuses on non-epileptic myoclonic disorders.