[Myoclonic dystonia]

Myoclonic dystonia is mainly described as a familial entity. Nevertheless it is also a syndrome. In the first part of this review we discuss the diagnostic difficulties of myoclonic dystonia which are mainly explained by the numerous denominations. In a second part, these entities (essential myoclonus, benign hereditary chorea, myoclonic dystonia with dramatic response to alcohol) are described, then grouped into one single disease, namely inherited myoclonic dystonia, To date, only benign hereditary chorea family, mapped to chromosome 14q, is still considered as a separate disease. In a third part, the main causes of myoclonic dystonia syndrome are described, with special focus on inherited myoclonic dystonia or myoclonus-dystonia. Numerous mutations are described on the epsilon-sarcoglycan gene located on chromosome 7q21. The function of epsilon-sarcoglycan is still unknown. The clinical features are predominant alcohol-sensitive myoclonus (neck, arms) with mild and more restrained dystonia (torticollis, writer's cramp). Obsessive-compulsive disorder may be associated with the disease. Promising treatments may be medical (gamma-hydroxybutyric acid) and surgical (deep brain stimulation) although therapeutic abstention may be possible owing to the frequent benign course of the disease.