To determine predictive and protective factors for autoimmune encephalitis (AIE) relapse including the use of chronic immunosuppression.

Approximately 25% of encephalitis cases are immune mediated. For most forms of AIE, risk of relapse is unclear and little evidence exists to guide which patients have the highest risk and whether ongoing immunosuppression reduces this risk.

We performed a chart review consisting of all patients with AIE presenting to the Calgary Neuro-Immunology Clinic between 2015 and 2020. Data was collected from 31 patients. Predictors of relapse, defined as worsening neurological clinical status after at least 2 months of stability or improvement without other cause, were determined.

Patients were followed for an average duration of 38 months, 14/31 (45%) relapsed during this time. Similar proportions of relapsing and non-relapsing patients (6/14 vs 9/17) were put on a steroid sparing agent after initial presentation. These included azathioprine, methotrexate, and rituximab. Possible predictors of relapse included abnormal CSF (69% vs 42%, p=0.12) and seropositivity (52% vs 33%, p=0.17), although neither reached significance. Earlier immunotherapy (207 vs 101 days, p=0.09) was protective against relapse. Patients with longer duration of steroid sparing agents prior to relapse as well as those on steroids at the time of relapse, had milder relapses (p= 0.04; p= 0.02) as determined by the Clinical Assessment Scale for Autoimmune Encephalitis (CASE). There was no difference in the proportion of patients on a steroid sparing agent at 3, 6 or 12 months between relapsing and non-relapsing groups.

Relapse risk in AIE is high (45%). Early treatment is effective in preventing relapse and continuous immunosuppression lessens the severity of relapse, although our study did not show it reduced occurrence of relapse before 12 months. Further studies are needed to determine if CSF and seropositivity can reliably predict relapse.