GAD autoantibodies have been associated with multiple neurologic syndromes, including stiff-person syndrome (SPS), limbic encephalitis (LE), and cerebellar ataxia (CA). Compared to SPS and LE, CA is rare and has poorly defined outcomes. Here, we review three cases, focusing on clinical presentations and therapeutic responses. 

Descriptive case series study.  

Patient 1: A 56-year-old man who developed gait instability and falls over the last 3 years. Neurological examination was notable for ataxic gait. Patient 2: A 45-year-old-men marathon runner presented with a 6-month history of inability to run and lack of hand coordination. Clinical findings revealed subtle dysmetria to finger-to-nose test and inability to perform tandem walk. Patient 3: A 75-year-old-woman presented with a constant vertigo, gait ataxia, and tendency to fall over the last 10 years. Her examination revealed multidirectional nystagmus, dysarthria, dysmetria on finger-to-nose, and ataxic gait. All patients ambulated with walkers during their initial evaluations. None of the patients had significant past medical history of autoimmune diseases or a family history of cerebellar ataxia. Paraneoplastic antibodies and malignancy workup were negative. Brain MRIs were normal in Patient 1 and 2. Patient 3’s MRI revealed cerebellar atrophy and abnormal signal involving the left hippocampus, amygdala, and anterior temporal cortex. All patients had markedly elevated anti-GAD antibody titers (2,610-25,000 nmol/L). Patient 1 and 3 received intravenous immunoglobulin and had excellent responses and were able to ambulate without walkers after 6 treatment cycles.

Anti-GAD associated CA is rare and its clinical presentation may hinder diagnosis. Persistent vertigo, gait instability, and cerebellar episodes can signal CA and should lead to anti-GAD antibody testing. Prompt immunotherapy is associated with good outcome. Clinicians should be able to recognize this treatable autoimmune CA.