Hyperekplexia: a syndrome of pathological startle responses.

We describe a family and three sporadic cases of startle disease, or hyperekplexia. Sudden unexpected noises caused the patients to fall rigidly, often injuring themselves but retaining consciousness. This unusual entity differs from startle epilepsy and cataplexy. Clonazepam proved ineffective in three patients. Valproic acid, 5-hydroxytryptophan, or piracetam markedly reduced the abnormal startle in three patients.