GAD65 Antibody–Associated Neurologic Disease Presenting With Hemiparkinsonism at Onset

A 60-year old previously healthy left-handed man presented to clinic with 6 months of progressive slowness and stiffness on the left side. He described loss of dexterity in the left hand and feeling of “heaviness” in the left leg. On exam, he exhibited mild bradyphrenia and hypophonia, moderate left arm and leg bradykinesia and rigidity, and left leg hesitations and reduced left arm-swing upon walking (video 1). A month prior, he had undergone MRIs of the brain and cervical spine with and without gadolinium that were unremarkable. Initial serum testing including complete blood count, comprehensive metabolic panel, thyroid stimulating hormone, ceruloplasmin, and vitamin B12 levels were all unremarkable. The differential diagnosis at presentation included the spectrum of parkinsonian disorders with Parkinson's Disease being the most likely given his age group and the asymmetric parkinsonism. He was diagnosed with suspected Parkinson's Disease and levodopa therapy was initiated as the he felt his symptoms were functionally-limiting.