Low-Titre GAD Antibody-Associated Late-Onset Cerebellar Ataxia with a Significant Clinical Response to Intravenous Immunoglobulin Treatment

Antiglutamic acid decarboxylase antibody-associated cerebellar ataxia (GAD-Abs CA) is a rare, but increasingly detected, autoimmune neurological disorder characterized by the clinical presence of a cerebellar syndrome concomitant with positive GAD-Abs levels in serum and cerebrospinal fluid (CSF). It represents 3% of all immune-mediated sporadic CAs. Low-titre GAD-Abs CA is an even rarer subtype of GAD-Abs CA. We report on a 68-year-old woman with a 3-year history of progressive gait ataxia. In addition to the modified Rankin Scale (mRS), we used two other objective scales to evaluate CA severity, i.e. the International Cooperative Ataxia Rating Scale (ICARS) and the Scale for Assessment and Rating of Ataxia (SARA). Series of CT and MRI showed atrophy of the cerebellum. Except for the glycated haemoglobin (HbA_1c) levels, all other routine laboratory examinations were within normal limits. Autoimmune laboratory examinations showed positive (25.8 U/mL) serum GAD-Abs levels. The GAD antibody index was <1.0. The CSF analysis showed no oligoclonal immunoglobulin bands. Intravenous immunoglobulin (IVIg) therapy was started and significant improvement was observed. The diagnosis of low-titre GAD-Abs CA was established.