Case Report: Clinical features and management of anti-mGluR1 encephalitis: case illustration and review of the literature.

Background: Anti-metabotropic glutamate receptor 1 (mGluR1) encephalitis is a rare autoimmune disease affecting cerebellar Purkinje cells. Only thirty-nine cases have been reported globally, with inconsistent documentation of treatments and outcomes. A systematic review is needed to identify prognostic factors and expand clinical understanding and treatment options.

Methods: Observational follow-up data of anti-mGluR1 encephalitis cases were collected. All anti-mGluR1 encephalitis cases published in the PubMed and Google Scholar databases in English before November 1, 2024 were included. Clinical information and possible predictive factors from both current and previously reported cases were statistically analyzed.

Results: We present a case of anti-mGluR1 encephalitis successfully treated with ofatumumab. During the patient's initial episode, she partially recovered after first-line treatment. She experienced a relapse 6 months later and was treated with ofatumumab, resulting in complete recovery. Forty cases of anti-mGluR1 encephalitis, including our case, were summarized. The prevalence was similar between men and women, with 50% of patients aged 40-59 years. The most common clinical manifestations were ataxia and dysarthria. Cerebrospinal fluid analysis showed normal white blood cell count and IgG index in 37.1% of patients. Almost half of the patients (48.6%) exhibited cerebellar atrophy on cerebral MRI scans at initial presentation or during follow-up. Only 25% of patients recovered completely. According to the modified Rankin Scale (mRS) scores at the last follow-up, patients with poor outcome (n = 13, 32.5%) had a lower proportion of first-line immunotherapy (62%, P = 0.017) and a longer follow-up time (median 36 months, P = 0.038).

Conclusion: The peak incidence of anti-mGluR1 encephalitis occurs between ages of 40-59 years. More than one-third of patients have normal cell counts and IgG index in the cerebrospinal fluid. Therefore, patients suspected of having this encephalitis should be tested for the presence of anti-mGluR1 antibodies in serum and cerebrospinal fluid. Notably, the first-line immunotherapy may be a critical factor influencing clinical outcomes.