Autoimmune cerebellar ataxia associated with anti-glutamate receptor δ2 antibodies: a rare but treatable entity

Abstract

Abstract We reported two novel cases of autoimmune cerebellar ataxia (ACA) associated with anti-glutamate receptor δ2 antibodies (Gluδ2-Abs). This first case was confirmed by indirect immunofluorescence and cell-based assays: a 29-year-old woman presenting, after 5 days of headache and vomiting, a pancerebellar syndrome, a downbeat nystagmus, a decreased visual acuity, and a lymphocytic pleocytosis in the cerebrospinal fluid (CSF) without any abnormality detected using cerebral magnetic resonance imaging (MRI). Clinical improvement was obtained progressively after second-line immunotherapy, full recovery was achieved after a 4-year follow-up. Thereafter, we retrospectively tested Gluδ2-Abs in 350 patients with a suspicion of autoimmune encephalitis without characterized autoantibody. We identified a second case, a 12-year-old boy developing, 10 days after a respiratory infection, a static cerebellar syndrome with lymphocytosis in the CSF and right cerebellum hyperintensity in MRI. Five days of corticosteroid treatment allowed a quick clinical improvement. No tumor was identified in both cases whereas laboratory analyzes revealed autoimmune stigma. The present cases suggested that ACA associated with Gluδ2-Abs is an extremely rare but treatable disease. Therefore, testing for Gluδ2-Abs might be considered in the setting of suspected ACA and no initial antibody identification. The visual deficits and ocular motility abnormalities observed in the first reported case might be part of the clinical spectrum of Gluδ2-Abs ACA. Young age, infectious prodromes, lymphocytic pleocytosis, and autoimmune background usually appear together with this syndrome and should lead to the prompt initiation of immunotherapy.