Effect of immunotherapy on intracranial EEG in patients with seronegative autoimmune‐associated epilepsy

Objective. Immunity is increasingly implicated in the aetiology of certain types of epilepsy, however, the clinical and EEG features in such cases remain poorly defined. We present stereo‐electroencephalography (SEEG) findings in patients who were thought to have autoantibody‐mediated epilepsy on the basis of clinical improvement after administration of immunotherapy (IT). Methods. All patients undergoing SEEG implantation in our service were reviewed and those receiving immunotherapy, either before, during, or after SEEG evaluation, were identified. Response to immunotherapy was defined as greater than 50% seizure reduction. We compared the clinical features and SEEG findings between those who responded to immunotherapy and those who did not. Results. Sixty‐two cases underwent SEEG evaluation. Of these, 11 received immunotherapy and three cases demonstrated a positive clinical benefit. The three responsive patients had multifocal seizure onset, repetitive spiking interictally and ictally, perisylvian semiology, seizure onset in the posterior perisylvian regions, and normal neuroimaging. Significance. Seronegative immunotherapy responders exist in epilepsy populations, therefore the diagnosis of autoimmune‐associated epilepsy should be considered before proceeding to epilepsy surgery. Possible features of an electroclinical syndrome associated with autoimmunity may include multifocal seizure onset, perisylvian involvement, and normal neuroimaging.