Benign neonatal sleep myoclonus: our experience of 15 Japanese cases.

PURPOSE: Benign neonatal sleep myoclonus is a non-epileptic movement disorder that may mimic neonatal seizures. The aim of this study was to clarify the clinical manifestations and outcomes in Japanese infants with benign neonatal sleep myoclonus.

METHODS: We reviewed the clinical manifestations and outcomes in 15 consecutive patients with benign neonatal sleep myoclonus (males: 10), including three paired familial cases, referred to our center between 1996 and 2011. The diagnosis of benign neonatal sleep myoclonus was based on a neonatal onset, characteristic myoclonic jerks that occurred during sleep, and normal electroencephalogram findings.

RESULTS: All were healthy full-term neonates at birth. The age at onset ranged from 1 to 18 days (median: 7 days). Prior to referral to our center (3-8 weeks), two infants had been placed on antiepileptic drugs, without effects. During the clinical course, the myoclonic jerks resolved by 6 months in 14 of the 15 patients. On follow-up (final evaluation, mean: 38 months), all but one patient (speech delay) showed normal development. None developed epilepsy. Of note, migraine occurred after 5 years of age in three children, including one who developed cyclic vomiting syndrome, evolving to migraine. Another boy developed cyclic vomiting syndrome, a precursor of migraine, before 1 year, and was being followed. A high incidence of migraine was observed in five (42%) of 12 parents whose detailed family history was available.

CONCLUSION: Our study suggests that benign neonatal sleep myoclonus is related to migraine. With the high rate of familial cases, further genetic study, including migraine-related gene analysis, is necessary to determine the underlying mechanism responsible for benign neonatal sleep myoclonus.