Long-Term Follow-Up of Non-Paraneoplastic Autoimmune Encephalitis: A Canadian Single-Center Experience.

Background: Autoimmune encephalidities (AIE) are becoming an increasingly recognized cause of encephalitis. While diagnosis and acute management are well described, information on long-term management and outcomes is limited. Given this, we reviewed 5 years of AIE patients, reporting on chronic management, relapse incidence and possible relapse predictors.

Methods: We performed a chart review of all patients with non-paraneoplastic AIE presenting to Calgary Neuro-Immunology Clinic and Tom Baker Cancer Centre between 2015 and 2020. Severity of relapse was determined using the Clinical Assessment Scale in Autoimmune Encephalitis (CASE). Variables were assessed with descriptive analysis and/or t-test.

Results: Patients were followed for a mean of 38.2 months. Outcome data were assessable in 37/38 patients. Relapse rate ranged from 0% (GFAP) to 67% (NMDA), with a mean of 46%. Most relapses (76%) occurred within 3 years. Time to treatment initiation at relapse was significantly shorter than initial presentation (p = 0.0015), and patients had less severe relapses compared to initial presentation (CASE score 5.18 vs 6.53; p = 0.040).Use of chronic immunotherapy did not appear to impact overall relapse risk, although patients on any immunotherapy at relapse had milder relapses based on ΔCASE (p = 0.0035).

Conclusion: Relapse was not uncommon (46%) for various AIE subtypes in our cohort, particularly within the first 3 years. Our data enforce the importance of long-term follow-up, which in our study allowed for earlier treatment and less severe relapses compared to initial presentation, as well as the need to further explore which patients would benefit from chronic immunotherapy.