Teaching Video NeuroImage: Subacute Cerebellar Ataxia in an Adolescent With Antibodies Against Metabotropic Glutamate Receptor Type 1

A 15-year-old boy developed progressive cerebellar dysfunction over 3 weeks. Examination showed ataxic gait, unsteady tandem gait, horizontal nystagmus, intention tremor, and ataxia on heel-toe-shin testing (Video 1, [links.lww.com/WNL/C323][1]). Dysdiadochokinesia and dysarthria were found but not illustrated in the video. Neuroimaging and CSF biochemistry was normal. Serum and CSF metabotropic glutamate receptor type 1 (anti-mGluR1) autoantibodies were found. His cerebellar function improved markedly within 3 months of initiating immunotherapy (Video 1, [links.lww.com/WNL/C323][1]). The median age at onset of anti-mGluR1 encephalitis is 55 years.1,2 Paraneoplastic syndromes should be considered, but anti-mGluR1 encephalitis is more often autoimmune in younger patients.1,2 [1]: http://links.lww.com/WNL/C323