False positive autoantibodies to glutamic acid decarboxylase in opsoclonus–myoclonus–ataxia syndrome after intravenous treatment with immunoglobulin

Additional investigations including extensive laboratory testing, CT-scan of the chest and abdomen, sonography of the testis, PET-scan of the body, dermatological evaluation and serological testing for anti-neuronal antibodies and infectious pathogens did not reveal a neoplastic, infectious, metabolic or toxic cause. Because of the rapid progression, intravenous immune globulin (IVIG) (0.4/(kgday)) was administered for 5 days, later followed by intravenous methylprednisolon (1000mg/day for 3 days). Anti-GAD measurement in our experience using a commercial ELISA is specific but seems, at least in our patient, to be able to lead to a false positive result as well. Because the incidence in the general population of anti-GAD is very low and predominantly associated with type I diabetes, it is unlikely that passive immunization was the cause of anti-GAD false positivity in our patient.