D ownbeat nystagmus (DBN) is a form of central vestibular nystagmus caused by various conditions (e.g., Chiari malformation, cerebellar degeneration, drug toxicity, nutritional deficiencies, and posterior fossa tumors). 1 Structural lesions of the cerebellar flocculus are a common pathology in DBN. 1 DBN may worsen when lying prone, in downgaze, or in lateral gaze. 1 Patients with DBN typically report oscillopsia, but may have other cerebellar signs (e.g., dizziness, postural imbalance, and gait ataxia). 1 Autoimmune antibodies and vitamin deficiency can produce DBN. We describe a case of antiparietal cell antibodypositive pernicious anemia that presented with vitamin B12 (VB12) deficiency and DBN, which rapidly improved after B12 supplementation. Based on our review of the English language ophthalmic literature, we believe that our case is novel.A 53-year-old woman developed acute onset of worsening persistent vertical oscillopsia. Medical history included previous bilateral refractive surgery, hypertension, and sarcoidosis in remission. She reported extensive workup for chronic intermittent tremors, dizziness, and joint pain, but never received a diagnosis. She had positive anti-nuclear antibodies titers (1:160 speckled), but never met criteria for systemic lupus erythematosus. She never smoked and decreased her alcohol consumption from 6 beverages per month to one drink per month. Her medications included celecoxib, cyclobenzaprine, losartan, meclizine, methocarbamol, and ondansetron. She had no dietary restrictions, normal body mass index, and denied an eating disorder or gastrointestinal surgery.Five months earlier, she was evaluated by neurology, otorhinolaryngology, and ophthalmology for new abnormal eye movements, blurry vision, imbalance, and difficulty
