Abstracts

RATIONALE: Myoclonic epilepsy is the uniform seizure type reported in association with the mitochondrial encephalomyopathies(ME.)However, in our experience, children with ME often present with multiple seizure types. METHODS: We performed a retrospective analysis of children diagnosed with ME, defined as defective oxidative phosphorylation detected in isolated mitochondria from skeletal muscle using polarographic techniques and/or DNA identifications of the commonly occurring mitochondrial mutations in blood. RESULTS: Medical records of 32 children with ME were reviewed. 9/32 presented with motor problems or developmental delay but never had seizures. Of the remaining 23,10 developed seizures in the first year of life while 13 ranged in age from 1 to 17 years at seizure onset. 10 children had refractory seizures, defined as failure to respond to 2 or more AEDs. These children had multiple seizure types, including various combinations of myoclonic, partial, absence, tonic and tonic-clonic seizures, usually with a severe accompanying encephalopathy. EEG findings in children with refractory epilepsy showed marked background abnormalities alone in 1 child, both multifocal and generalized epileptiform discharges in 5, generalized slow spike wave in 1, while 3 children showed focal discharges with or without secondary generalization. EEG findings in children with nonrefractory seizures were also varied. Mitochondrial defects were equally distributed between respiratory chain, Krebs cycle and mitochondrial DNA mutations in children without seizures and in children with refractory and non refractory epilepsy. CONCLUSIONS: ME should be considered in the differential diagnosis of children with seizures of unclear etiology in the early years of life. Seizure types and EEG abnormalities are varied and do not correlate with specific biochemical defects.