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Benign sleep myoclonus in infancy is a distinctive but underdiagnosed disorder of quiet sleep, which according to our findings occurs from the first day of life up to age 3 years. Its main features are rhythmic myoclonic jerks when drowsy or asleep, which stop if the child is woken, and normal encephalograms during or after the episodes. 1 2 When all these features are present the diagnosis should be clear cut. The diagnosis may be difficult if the association with sleep is not noted and if no attempt is made to stop the "seizures" by waking the child. We report on15 patients in whom benign sleep myoclonus was initially mistaken for epilepsy.
Patients
All the patients were referred during the five year period 1996â[euro]"2001 for investigation and treatment of prolonged "seizures"; some had been given anticonvulsants, without effect. The table summarises the clinical details of all the patients.
Illustrative case
A 14 day old boy (case 1; see table) was admitted after emergency helicopter transfer. In the previous week he had had several episodes of what was assumed to be status epilepticus but these had failed to respond to rectal and intravenous diazepam. Phenobarbitone and then phenytoin had been added but the seizures had continued. When he reached hospital he had been having generalised myoclonic movements for one hour. He was receiving three anticonvulsants in high doses. After the "seizure" ceased he appeared well but was drowsy. He fed well. Spontaneous movements and newborn and positional reflexes were normal.
Encephalograms during and after the episodes showed excess beta activity with generalised slowing, which was ascribed to his medication. There was no epileptic activity. The results of ultrasound and magnetic resonance imaging of his brain were normal, as were concentrations of plasma calcium, magnesium, glucose, ammonia, and urinary amino acids and organic acids.
Despite triple anticonvulsant therapy the "seizures" recurred and he was given repeated doses of diazepam,...