Favorable Outcome with Intravenous Immunoglobulin Therapy in Late-Onset Anti-mGluR1 Encephalitis: A Case Report and Literature Review.

Anti-metabotropic glutamate receptor 1 (mGluR1) encephalitis is a rare autoimmune disorder manifesting with cerebellar syndrome. Patients with mGluR1 encephalitis have been treated with immunomodulatory therapies; however, little is known about the efficacy of this therapy. A 58-year-old Japanese woman presented with dizziness when walking and standing up. Symptoms persisted and the patient gradually deteriorated. The neurological examination revealed a broad-based gait, horizontal and slightly gaze-evoked nystagmus, noticeable head titubation, and truncal ataxia without limb ataxia. Magnetic resonance imaging was normal. The ¹²³I-isopropyl-iodoamphetamine single-photon emission-computed tomography scans showed normal cerebellar perfusion. Based on a positive antibody test for anti-mGluR1, the patient was diagnosed with anti-mGluR1 encephalitis. She was treated with intravenous methylprednisolone and intravenous immunoglobulin (IVIg). Symptoms gradually improved over 1 month and almost disappeared after additional IVIg therapy. Anti-mGluR1 encephalitis is a rare disease, and effective treatment is unclear. In this case, a favorable outcome was obtained with immunomodulatory therapy, even though the neurological disability of the disease course is worse. We emphasize the importance of early diagnosis and therapeutic intervention, suspecting the disease on the basis of its characteristic symptoms.