Background The longer-term trajectory of seizures associated with autoimmune encephalitis (AIE) is not clear. Recent data in NMDA AIE suggests seizures manifest early and are generally short lived, but in LGI1 AIE they occur later and continue longer. We characterised seizure semiology and associated prognosis in two cohorts of AIE patients.

Methods Case note review of 14 patients with a ‘definite’ diagnosis of anti-NMDAR AIE and 14 patients with LGI1 AIE showed the latter to occur in older adults. Patients were categorized as having seizures within one month of presentation or no seizures and the semiology was classified as focal or generalised onset.

Results In the NMDA group A, 3/7 patients (23%) had focal onset compared to 6/11 patients (55%) in the LGI1 group, with predominantly faciobrachial dystonic seizures. NMDA patients were more likely to be seizure-free at 6 months (9/12, 75%) compared to LGI1 patients (6/14, 43%). Similarly, much fewer NMDAR patients remained on ant-epileptic medications at 1 year compared to the LGI1 patients. Neither seizure semiology at presentation nor presence of inflammation on MRI correlated with longer term seizure trajectory in both groups.

Conclusion Seizures are common presenting symptoms in these AIE groups. More NMDA patients were seizure-free at 6 months and did not require AEDs after 1 year compared to the LGI1 patients. LGI1 patients represented a more susceptible group of AIE patients to epilepsy.