Autoimmune brainstem encephalitis: Clinical associations, outcomes, and proposed diagnostic criteria.

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We describe neurologic phenotype, clinical associations, and outcomes in autoimmune brainstem encephalitis. Medical records of neural-IgG positive autoimmune brainstem encephalitis patients diagnosed at Mayo Clinic (January 1, 2006-December 31, 2022) were reviewed. Ninety-eight patients (57 male) were included. Median age of symptom onset was 51 years (range, 8 months-85 years). Frequent presenting features were ≥1: diplopia (80%), ataxia (78%), dysarthria (68%), vestibulocochlear symptoms (67%), dysphagia (61%), nausea/vomiting (42%), and facial weakness (32%). Altered mental status (11%) was uncommon. Neural antibodies detected were as follows: KLHL-11 (26 patients), GAD65 (high titer, 12), ANNA-1 (anti-Hu, 8), ANNA-2 (anti-Ri, 8), Ma2 (7), IgLON-5 (6), AQP4 (6), MOG (4), glycine receptor (4), GQ1B (4), PCA-1 (anti-Yo, 4), DPPX (2), neurochondrin (2), neurofilament (2), NMDA-R (2), AGNA-1 (SOX-1, 1), ANNA-3 (DACH1, 1), amphiphysin (1), CRMP-5 (1), ITPR-1 (1), PCA-Tr (DNER, 1), and PDE10A (1). Cancer was identified in 55 patients: germ cell (23 patients; 3 extra-testicular), ductal breast adenocarcinoma (8), small cell carcinoma (6, lung 4), adenocarcinomas (6), neuroendocrine carcinoma (3), hematologic (2), squamous cell (2), and other (7). Median modified Ranking score (mRS) at last follow-up was 3 (range, 0-6). Factors associated with poor outcome included abnormal brain MRI, bulbar symptoms, and elevated CSF IgG index. Kaplan-Meier analysis revealed faster progression to wheelchair in patients who were immunotherapy refractory and with elevated CSF IgG index. Diagnostic criteria for autoimmune brainstem encephalitis (definite and probable) are proposed. Autoimmune brainstem encephalitis is a distinct clinical subphenotype of autoimmune encephalitis. Abnormal brain MRI, bulbar symptoms, and elevated CSF-IgG index associate with poor outcome.