Severe myoclonic epilepsy associated with mitochondrial cytopathy

We describe a case in which severe myoclonic epilepsy of infancy is associated with a disturbance in mitochondrial function. EEG traces showed diffuse spike-wave patterns inducible by intermittent photic stimulation. Laboratory analyses revealed high lactic acid levels in cerebrospinal fluid and urine, without metabolic acidosis or high lacticacidaemia. Muscle biopsy showed a slight increase in the number of mitochondria, which had a tendency towards subsarcolemmal locations, and clefts in the myofibrillar membrane that contained granular material staining positive for oxidative enzymes and red with modified Gomori stain. Quantification of the enzymatic activities of homogenized muscle showed partial deficiency of the mitochondrial respiratory chain complexes III and IV. Severe myoclonic epilepsy associated with mitochondrial cytopathy was diagnosed, but the possibility cannot be ruled out that the myoclonic epilepsy (or perhaps simply nonspecific epileptic encephalopathy) was secondary to the mitochondrial cytopathy. Thorough diagnostic analysis in severe myoclonic epilepsy cases is called for with a view to elucidation of a possible metabolic aetiology.