Clinical Phenotypes and Prognosis of Anti-mGluR1 Encephalitis: A Single-Center Case Series and Comprehensive...

Background/Objectives: Anti-mGluR1 encephalitis is a rare form of autoimmune encephalitis predominantly manifesting as acute/subacute cerebellar ataxia. We describe a newly diagnosed case series from our center and conduct a comprehensive review of reported cases worldwide to compare clinical manifestations, treatment options, and outcomes. Methods: We consecutively identified 11 patients at Peking Union Medical College Hospital, and additionally extracted clinical data from 42 previously published cases identified via PubMed and Google Scholar (search updated to 1 August 2025). Demographics, phenotypes, laboratory findings, imaging, treatment, and outcomes were systematically summarized. This pooled review was not prospectively registered, and extracted data from 21 published articles were analyzed alongside our 11 newly diagnosed cases. Results: The integrated cohort comprised 53 patients with anti-mGluR1 encephalitis, including 29 males and 24 females, with patients reported from Asia (n = 18), North America (n = 11), and Europe (n = 24). The median age at onset was 50 years (IQR 29.5-58.5; range 3-81), with North American patients presenting later than their Asian and European counterparts (median 60 vs. 48 and 45 years, respectively; all p < 0.05). Disease onset was subacute in most cases (58.7%). Comorbid tumors were present in nine patients, most commonly lymphomas. Clinical phenotypes were classified as pure cerebellar syndrome (n = 31), cerebellar ataxia with encephalitic features (n = 20), and non-cerebellar presentations (n = 2). Baseline severity differed across phenotypes (χ² = 35.7, p < 0.001). Regional variability in severity was observed but did not reach significance. CSF analyses revealed pleocytosis in 59% (23/39), elevated protein in 31.3% (5/16), and oligoclonal bands in 52.2% (12/23). MRI abnormalities were detected in 34.7% (17/49) of patients, with 21.9% (7/32) developing cerebellar atrophy on follow-up. Therapeutic strategies varied significantly across regions (p = 0.041), with Asian cohorts more frequently receiving long-term immunosuppression, European cohorts favoring combined regimens, and North American cases relying predominantly on first-line therapies. Overall, 65.9% (29/44) of patients clinically improved, 13.6% (6/44) relapsed and 20.5% (9/44) remained unaffected. Conclusions: Anti-mGluR1 encephalitis presents with significant clinical heterogeneity, ranging from cerebellar-dominant ataxia to neuropsychiatric or non-cerebellar phenotypes, and demonstrates differences in reported age of onset, disease severity, and therapeutic approaches across publication regions. Our findings underscore the importance of early recognition, sustained immunotherapy, and international collaboration to establish standardized, evidence-based management for this rare but disabling disorder.