Cognitive Decline in Severe Intractable Epilepsy

PURPOSE: To explore the relation between seizure-related variables and cognitive change in patients with severe intractable epilepsy. METHODS: A retrospective analysis of data from 136 patients who had undergone a cognitive assessment on two occasions at an interval of > or =10 years. Cognitive measures included tests of memory and executive skills in addition to intelligence quotients (IQ). Details were available regarding seizure type and frequency in the intertest interval. RESULTS: Cognitive decline was severe and occurred across a wide range of cognitive functions. The frequency of generalised tonic-clonic seizures was the strongest predictor of decline. Complex partial seizure frequency was associated with a decline in memory and executive skills but not in IQ. Seizure-related head injuries and advancing age carried a poor cognitive prognosis, whereas periods of remission were associated with a better cognitive outcome. Early age at onset was not implicated, and duration of epilepsy was a much less potent predictor of cognitive decline than has been reported in cross-sectional studies. No evidence indicated that a higher level of cognitive function protected against cognitive decline. CONCLUSIONS: Our findings, together with those from animal studies and surgically treated patients, suggest that seizures can have a direct adverse effect on cognition and that good seizure control even after years of intractability can have a beneficial impact on cognitive prognosis. This study was based on individuals who merited two cognitive assessments > or =10 years apart and hence is biased in favor of those with the most severe forms of refractory epilepsy and those with decline.