Rationale: Medial medullary infarction accounts for less than 1% of brain infarctions, and medial medullary infarctions is very rarely caused by antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. Patient concerns: We report the case of a 76-year-old man at low risk of arteriosclerosis who presented with disorders on the left side including gaze-evoked nystagmus, paralysis of the extremities, pyramidal signs, sensory disturbance, and dysesthesia. Brain magnetic resonance imaging also showed right medial medullary infarction. Diagnoses: Medial medullary infarction caused by ANCA-related vasculitis was diagnosed based on mild renal dysfunction and high levels of blood leukocytes, C-reactive protein (CRP), and myeloperoxidase (MPO)-ANCA. Interventions and outcomes: He underwent two 3-day courses of steroid pulse therapy involving daily 1000 mg doses of methylpredonine. He then received 30 mg/day (0.5 mg/kg/day) of prednisolone (PSL) without other immunosuppressants. Levels of MPO-ANCA and the inflammatory marker CRP decreased rapidly a month after admission. Once MPO-ANCA became undetectable, the PSL dose was carefully reduced to 10 mg/day. To treat his paralysis, we provided rehabilitation with a Hybrid Assistive Limb five times starting at a month post-onset. His Barthel index score rose from 45 to 70 points. Lessons: Medullary infarction is mostly caused by arteriosclerosis and vertebral arterial dissection. When systemic inflammatory findings are obtained, ANCA-associated vasculitis should be considered a potential cause, and steroid pulse therapy should be promptly administered.
