Efficacy of early rituximab treatment in anti-mGluR1 encephalitis: a case report.

Background: Anti-mGluR1 encephalitis is a form of autoimmune encephalitis, with limited reports globally and only two cases reported from Japan. There are uncertainties regarding the optimal immunosuppressive agents and individual drug responses. Herein, we report a case of anti-mGluR1 encephalitis from Japan, notable for a favorable outcome after an early rituximab initiation and an observed increase in cerebellar blood flow during the early disease stages.

Case presentation: The patient was a 65-year-old woman who experienced dizziness for 3 months, followed by worsening gait instability. She was referred to our department due to progressive difficulty standing and walking. Neurological examination revealed dysarthria, severe cerebellar ataxia, and impaired performance on the finger-to-nose and knee-to-heel tests. Blood tests were negative for rheumatologic autoantibodies, and cerebrospinal fluid (CSF) analysis showed a cell count of 4/µL and a protein level of 40.0 mg/dL. However, the IgG index was elevated at 1.35, and oligoclonal bands were positive. Brain magnetic resonance imaging showed no abnormalities, but ¹²³I-iodoamphetamine single-photon emission computed tomography revealed mild hyperperfusion in the bilateral cerebellar hemispheres. Based on the clinical presentation, immune-mediated cerebellar ataxia was suspected. The patient was treated with intravenous methylprednisolone, oral prednisolone, and intravenous immunoglobulin. Further diagnostic testing using tissue- and cell-based assays detected mGluR1 antibodies in pretreatment serum and CSF, confirming the diagnosis of anti-mGluR1 encephalitis. As the initial treatment was insufficient, rituximab was administered, leading to significant improvement, including the ability to walk unaided. At the most recent follow-up, >6 months postonset, she showed no symptom progression or cerebellar atrophy.

Conclusions: We experienced a case of anti-mGluR1 encephalitis with increased cerebellar blood flow, where early RTX administration led to a favorable outcome. Its early use, as an acute treatment and for maintenance, may help prevent recurrence and contribute to a positive prognosis.