Anti-GAD antibodies and periodic alternating nystagmus

BACKGROUND: Autoantibodies directed against glutamic acid decarboxylase (GAD-Ab) have recently been described in a few patients with progressive cerebellar ataxia, suggesting an autoimmune physiopathologic mechanism. OBJECTIVE: To determine the exact role of GAD-Ab and gamma-aminobutyric acid (GABA)-ergic neurotransmission in the pathogenesis of cerebellar ataxia. DESIGN: Case report. SETTING: University neurological hospital. PATIENT: We report the case of a patient with subacute cerebellar ataxia associated with GAD-Ab showing periodic alternating nystagmus (PAN). INTERVENTION: Baclofen, a GABAergic medication, was given to the patient. MAIN OUTCOME MEASURES: Eye movement recording of spontaneous nystagmus and postrotatory vestibular responses. RESULTS: Baclofen was effective in suppressing PAN and improving postrotatory vestibular responses but not for improving cerebellar ataxia. CONCLUSION: The presence of PAN and the response to baclofen provide a unique opportunity to suggest a direct role of GAD-Ab in cerebellar dysfunction in this patient.