A 64-year-old African American woman with a family history of autoimmune disease and breast cancer presented with a three-week history of progressive lower extremity weakness, gait imbalance, and multiple falls. Examination revealed spastic asymmetric (right greater than left) quadriparesis, hyperreflexia, upgoing plantar responses, dysmetria in the upper and lower extremities, and impaired proprioceptive and vibratory sensation. MRI showed a longitudinally extensive FLAIR hyperintense signal extending from the cervicomedullary junction through the thoracic cord involving the dorsal columns and right hemicord with subtle dorsal subpial enhancement. Electrodiagnostic studies demonstrated axonal polyneuropathy with acute denervation. Chest CT identified multifocal pneumonia. Thorough malignancy screening was negative. Serum and CSF neural autoantibodies were negative. Serologic testing was positive for myeloperoxidase antibodies with a p-ANCA pattern. Lung and renal biopsies confirmed ANCA-associated vasculitis. She was treated acutely with pulse corticosteroids, plasma exchange followed by induction with 6-month maintenance dosing. At 15-month follow-up she is ambulatory with mild-moderate residual ataxia with improvement in MRI and near resolution of EMG/NCS findings.