Present two cases of cerebellar disease due to anti-GAD65 antibodies. Both patients presented with symptoms localizable to the cerebellum by vestibular testing when bedside exam could otherwise be misdiagnosed as functional. One patient received early vestibular testing for nystagmus while the other had symptoms for about 4 years before diagnosis and progressed to epilepsy. This highlights the importance of considering anti-GAD65 disease in workup for ataxia and dizziness.  

Anti-GAD65 antibody neurologic disease is rare but relatively understood autoimmune disease. The pathogenicity of the antibody is debated and clinical correlation is paramount. Several neurological syndromes are well associated to GAD65 antibodies including stiff-person syndrome, cerebellar ataxia and epilepsy. Patients with rare diseases receive 3 diagnoses and see 5 physicians prior to correct diagnosis (4).

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Both patients exhibit a neurologic syndrome well-associated with anti-GAD65 antibodies. They also presented with symptoms that could have been misdiagnosed as functional. Knowledge of these syndromes and workup for anti-GAD65 is crucial to detecting immune-mediated disease and timely treatment. Early vestibular testing can detect CNS patterns of nystagmus, especially if other signs of ataxia are subtle to subsequently inform appropriate testing for GAD65.