Epidemiology and treatment of epilepsy in patients who are mentally retarded

Epilepsy affects approximately 14 to 24% of patients who are mentally retarded. The prevalence increases in those patients who have associated neurological disorders. The severity of mental retardation also influences prevalence. Approximately 7 to 15% of patients with mild to moderate mental retardation, 45 to 67% of those with severe retardation and about 50 to 82% of patients with profound retardation have a lifetime history of epilepsy. The prevalence of epilepsy also varies according to patients' age and the aetiology of mental retardation. Both false positive and false negative diagnoses of epilepsy remain possible in patients who are mentally retarded. Polytherapy with anticonvulsants is a commonly used approach to the treatment of epilepsy in patients with mental retardation. However, a reduction in polytherapy has been shown to improve both seizure frequency and the behavioural profile of these patients. Because of the cognitive and behavioural adverse effects of barbiturates and the effect of phenytoin on the CNS, they are not ideal as drugs of First choice in patients with epilepsy who are mentally retarded. Both valproic acid (sodium valproate) and lamotrigine are favoured for use in these patients because of their broad spectrums of anticonvulsant activity and thus efficacy in different seizure types, effects in Lennox-Gastaut syndrome, and minimal effects on cognition and behaviour. The use of carbamazepine is restricted in certain seizure types but can be chosen for some patients who are mentally retarded because of its mood stabilising properties. Oxcarbazepine has similar properties to those of carbamazepine but with a better tolerability profile. Vigabatrin, felbamare, gabapentin. topiramate, tiagabine and zonisamide are also useful, particularly as add-on therapy. Serious adverse events. such as visual field defects caused by vigabatrin. and fatal blood dyscrasias and hepatotoxicity associated with felbamate, will restrict the use Of these drugs in this population. Neurosurgical treatment has been proven effective in a number of patients with epilepsy who are mentally retarded.