Spasms in children with definite and probable mitochondrial disease.

The diagnosis of mitochondrial encephalomyopathies is complex and a system for classification of the diagnosis as definite, probable, and possible has been proposed. The objective of this study was to explore the spectrum of epileptic disorders associated with probable and definite mitochondrial disease in children using this classification system. The patient population with mitochondrial disease and epilepsy was selected from a tertiary care children's hospital. Interictal electroencephalograms and video-EEG recordings were used to characterize seizure types. Ten children fulfilled the criteria for probable or definite mitochondrial disease and had epilepsy. Four had siblings with a similar clinical phenotype. Spasms were the most common seizure type and were the initial seizure type in seven patients and two siblings. Four patients had only partial seizures, with or without generalization, and one patient had seizures that were difficult to classify. Blood lactate concentrations were elevated consistently in patients with partial seizures alone but were occasionally normal in children with spasms. Spasms were the most common presenting seizure type in children with probable and definite mitochondrial disease.