GAD65 associated neurological syndromes are rare with variable clinical presentation and laboratory and imaging findings. MRI Brain abnormalities have not been well characterized.

Cases of GAD65 antibody positive neurologic disorders were identified by searching Ochsner health network records 2013 to 2023. Patients with positive GAD65 serum or cerebrospinal fluid (CSF) testing and abnormal brain MRI findings were included.

Of 49 patients with positive GAD65 antibody in serum and/or CSF, 5 patients had abnormal brain MRI (10%). Four cases were diagnosed as encephalitis and one case as cerebellar ataxia. Patients with GAD65 encephalitis were female with age range of 18 to 65 years old. The two younger patients presented with new onset seizures, one with abnormal left temporal and the other right temporal T2 hyperintense MRI signal, GAD titer 0.09 nmol/L and 1620 nmol/L respectively. Of the two older patients with clinical symptoms of encephalitis, one had a history of craniopharyngioma with residual suprasellar tumor on MRI and presented with confusion and hallucinations (GAD titer 11.20 nmol/L). The other had MRI with T2 hyperintense left midbrain signal after presenting with right-sided ataxia and weakness with dysarthria, and her GAD65 encephalitis diagnosis preceded several malignancy diagnoses, including glioma (GAD titer 4.72 nmol/L). The case of cerebellar ataxia occurred in a male patient with prior diagnosis of late autoimmune diabetes of adults and no immunosuppressant use (GAD titer 72.80 nmol/L). MRI showed cerebellar atrophy without contrast enhancement.

Brain MRI abnormalities are rare in patients with GAD65 associated neurological syndromes. Changes can include temporal lobe abnormalities in patients with epilepsy, cerebellar atrophy in patients with cerebellar ataxia, and CNS tumors.