Benign neonatal sleep myoclonus: history and semiology.

Benign neonatal sleep myoclonus is a condition characterized by myoclonus occurring during sleep. Reported here are 18 cases of infants who had electroencephalographic monitoring, with myoclonic events recorded in 17 cases. In all cases, onset was within days to a few weeks of birth. In no case was the diagnosis of sleep myoclonus considered by the referring primary care physician. Myoclonus was evident during sleep in all 18 infants, but in two of them it was observed also during the transition from sleep to awakening. The behavioral features of the disorder were more varied than previously described: four of the infants had lateralized myoclonus and two had myoclonus involving the head and face. In most of the children, the duration of myoclonus was brief, but in two cases the paroxysmal events lasted more than 30 minutes. None of the children had electroencephalographic abnormalities during the myoclonus. The condition was short-lived, with the myoclonus resolving in most children within 3 months of onset. Benign neonatal sleep myoclonus is an under-recognized condition but one that has a consistently favorable outcome. Infants with the condition should not be treated with antiepileptic drugs.