Limbic encephalitis as a precipitating event in adult-onset temporal lobe epilepsy

Objective: Temporal lobe epilepsy with hippocampal sclerosis (TLE-HS) is the most frequent diagnosis in autopsy and surgical epilepsy series. TLE-HS usually starts during childhood or adolescence. There have been few studies of adult-onset disease. We recognized that some adult individuals have evidence of limbic encephalitis (LE), an autoimmune condition of adult life, which we proposed might lead directly to this syndrome. Methods: We performed a retrospective analysis of history, clinical and paraclinical findings, brain MRI, and outcome of surgical treatment including histopathology (if available) of all patients with TLE-HS presenting to this tertiary center within 6 years of epilepsy onset between 1999 and 2005. Results: Thirty-eight patients were identified, with median age at epilepsy onset of 37.8 years. Eleven patients (29%) were classified as having secondary HS (e.g., after head trauma, febrile seizures). Seven patients (11%) were classified as idiopathic. However, 9 patients (24%) had a diagnosis of definite LE, and another 11 individuals (29%) showed the typical LE pattern of MRI findings with hippocampal swelling evolving into atrophy with continuous FLAIR/T2 signal increase; they were diagnosed as possible LE. Bilateral abnormalities were more frequent in the two LE subgroups (60%) than in the two non-LE subgroups (22%; p = 0.025). Histopathology was performed in one patient with possible LE shortly after disease onset and showed a typical T cell infiltration and loss of hippocampal neurons. Conclusions: Temporal lobe epilepsy with hippocampal sclerosis can manifest in adult life. Around half the patients have evidence consistent with an autoimmune process. If confirmed, this should have implications for diagnosis, prevention, and treatment.