Propylthiouracil-induced myeloperoxidase antineutrophil cytoplasmic antibody-associated leukocytoclastic vasculitis.

Propylthiouracil (PTU), an antithyroid medication used in managing Graves disease, can rarely cause antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), a potentially serious complication. We report a case of a 54-year-old woman with Graves disease on long-term PTU therapy who developed a progressive purpuric rash and polyarthralgia. Laboratory tests showed elevated inflammatory markers and positive results for perinuclear ANCA (p-ANCA) and myeloperoxidase antibodies. A skin biopsy confirmed leukocytoclastic vasculitis. Symptoms improved after the discontinuation of PTU and initiation of corticosteroid therapy. The patient subsequently underwent total thyroidectomy for definitive treatment of Graves disease. This case highlights the importance of considering PTU-induced AAV in patients with vasculitic rashes, even after years of stable therapy. Early detection, prompt discontinuation of the medication, and multidisciplinary collaboration are essential to prevent disease progression and ensure favorable outcomes.