The treatment of severe action myoclonus.

Ten patients with severe disabling myoclonus were treated with clonazepam, sodium valproate, primidone and piracetam alone, or in different combinations. Electrophysiological assessment indicated a cortical origin for the myoclonus in every case. Considerable improvement of myoclonus was achieved with combinations of these drugs in all patients, but this was not possible with monotherapy. In one patient two drugs were necessary (clonazepam and piracetam); in the others more than two drugs were required. The combination of sodium valproate, clonazepam and primidone (3 patients), or piracetam, clonazepam and primidone (3 patients), or the four drugs together (3 patients) was necessary to provide substantial relief of myoclonus. Such polytherapy generally was tolerated well. The benefits of treatment continued for more than 1 year in all cases, although progressive underlying pathology often caused other increasing disability.