Vertical nystagmus associated with glutamic acid decarboxylase antibodies responding to cyclophosphamide

Several neurological disorders have been described in patients with autoimmunity associated with GAD antibodies. Among these disorders, nystagmus and oculomotor dysfunction are increasingly recognized, although they have been rarely reported isolated or as the main manifestation of anti-GAD autoimmunity. Moreover, therapeutic approaches for such patients are unclear. Here we present a 44-year-old man with disabling oscillopsia secondary to downbeat nystagmus, abnormal saccades, ocular pursuit and optokinetic nystagmus, as well as mild gait ataxia and cerebellar atrophy associated with high serum GAD antibodies with intrathecal secretion of such antibodies. The patient did not have clinical benefit with plasma exchange, but had a robust symptomatic improvement with cyclophosphamide. We discuss the possible pathogenic role of GAD antibodies in nystagmus and the role of immunotherapy in these patients.