Anti-GAD Associated Cerebellopathy and Bilateral Vestibulopathy

This is a 70-year-old woman with the subacute onset of severe imbalance and dizziness. On her initial examination, she had prominent gaze-evoked nystagmus and bilateral vestibular loss. Smooth pursuit was saccadic, although her vestibulo-ocular reflex (VOR) suppression was much smoother. Usually pursuit and VOR suppression are both normal or both saccadic, but when pursuit is impaired and there is bilateral vestibular loss, there is no VOR to suppress, so VOR suppression can look normal or better than pursuit. Her visually-enhanced VOR (slowly rotating the head side to side while the patient fixates on the examiner's nose) was also saccadic given impaired pursuit and loss of vestibular function. Her anti-GAD antibody titer came back very high, and she was admitted for expeditious paraneoplastic work-up and therapy with IV immunoglobulin. There was a substantial improvement in symptoms and signs when she returned one month after being discharged from the hospital. Her gaze-evoked nystagmus was much less prominent, pursuit was only mildly saccadic, and her previously + head impulse testing was only minimally abnormal. Going along with vestibular and cerebellar improvement was also mildly choppy VOR suppression which was now proportional to her mildly saccadic pursuit - this suggested that there was now some VOR to suppress. Her visually enhanced VOR was also less saccadic, also suggestive of vestibular and/or pursuit improvement.