Cognitive adverse events of topiramate in patients with epilepsy and intellectual disability.

Topiramate (TPM) is an effective antiepileptic drug (AED). A high proportion of patients, however, experiences cognitive adverse events (CAEs), especially in verbal fluency, memory spans, and working memory. To our knowledge, CAEs of TPM have not been studied systematically in patients with intellectual disability (ID). This may be due to the fact that many of those patients are not able to follow test instructions properly and that neuropsychological instruments are not validated for that group. Cognitive deterioration in patients with ID may thus easily be overlooked. Topiramate is in frequent use in persons with ID. We included 26 consecutive patients with epilepsy and ID in this observational study who had undergone neuropsychological examinations as part of clinical routine before and after the introduction of TPM into the therapeutic regimen (n=4) or before and after the withdrawal of TPM (n=22). Examinations under TPM showed reduced cognitive speed, reduced verbal memory, reduced verbal fluency, and reduced flexibility compared to examinations without TPM. Despite some limitations (especially small sample size, high interindividual variation of the results dependent on the degree of ID, effects of other - limited - changes in the therapeutic regimen), our study indicates that TPM in persons with epilepsy and ID may lead to CAEs comparable to those in persons with normal intelligence. Neuropsychological testing is mandatory in order not to miss CAEs that might severely impair quality of life.