Case of subacute cerebellar ataxia with anti‐glutamic acid decarboxylase antibodies in cerebrospinal fluid, but not in serum

A 67‐year‐old woman presented with dysarthria and trunk and limb ataxia, which progressed in a subacute manner. Anti‐glutamic acid decarboxylase antibodies were negative in the serum, but were detected in the cerebrospinal fluid. Steroid pulse therapy was administered on the suspicion that the presence of anti‐glutamic acid decarboxylase antibodies in the cerebrospinal fluid might be associated with cerebellar ataxia. Treatment resulted in a marked improvement in clinical symptoms, leading to a diagnosis of anti‐glutamic acid decarboxylase antibody‐positive cerebellar ataxia. The outcome showed that measuring anti‐glutamic acid decarboxylase antibodies levels in the cerebrospinal fluid is important, even when levels are negative in the serum.