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.