INTRACTABLE EPILEPSY IN A POPULATION-BASED SERIES OF MENTALLY-RETARDED CHILDREN

Purpose: The characteristics of intractable epilepsy were analyzed in a population-based study of active epilepsy in mentally retarded child ren aged 6-13 years. Methods: Diagnostic registers, EEG laboratory reg isters, and registers for the Education of the Subnormal were searched . Medical files were scrutinized. Clinical examinations and interviews with parents and caregivers or both were performed. EEG recordings, c omputed tomography (CT) and magnetic resonance imaging (MRI) of the CN S were reevaluated. Results: Forty-five percent (44 of 98) of the chil dren with mental retardation (MR) and active epilepsy had intractable seizures, defined as one or more seizures every day or week. The media n age at onset was 0.8 years, as compared with 3.0 years for those wit h controlled epilepsy. Predictive factors for frequent seizures were t he number of seizure types, severe MR, status epilepticus (SE) and ton ic seizures. Epileptiform EEG activity was present in 91%, and focal a ctivity in 65%. Brain lesions were detected on CT and MRI in 70%, with generalized lesions in 60%. Concurrent focal epileptiform activity an d focal brain lesions on CT/MRI were detected in 26%. The percentages and prevalence rates for infantile spasms (IS) and Lennox-Gastaut synd rome (LGS) were 18% (0.25 in 1,000) and 7% (0.06 in 1,000), respective ly. One of 8 children with IS had had previous neonatal seizures, 3 ha d SE and 1 later developed LGS. Conclusions: Children with MR and intr actable epilepsy have a high frequency of severe MR and additional maj or neuroimpairments. EEG recordings frequently showed focal changes de spite generalized lesions in neuroradiology.