Continuous muscle fibre activity (Isaacs' syndrome) in infancy: a report of two cases.

Two cases of continuous muscle fibre activity in infancy are reported. Both infants were severely affected and died from respiratory failure. Treatment with phenytoin and carbamazepine produced only temporary improvement. Electrophysiological and pharmacological evidence suggests that the site of the lesion in infancy, as in older patients, is in the terminal nerve endings or motor end plate. Continuous muscle fibre activity occurring in infancy seems to be more severe than in older children or adults and seems refractory to treatment.