Hereditary essential myoclonus.

A family is reported in which 11 members in 4 generations had a benign form of essential myoclonus of early onset. The myoclonic jerks were mostly asynchronous and dysrhythmic. They occurred spontaneously when relaxed, induced by movement, increased in tonus and emotional stress. Generalized seizures was found in 3 members who also had essential myoclonus. The relationship between essential myoclonus and idiopathic epilepsy was stressed. Beneficial effect was obtained with alcohol and clonazepam.