MON-357 - Propylthiouracil-Associated Myeloperoxidase Antineutrophil Cytoplasmic Antibody-Associated Leukocytoclastic Vasculitis

Background:
Propylthiouracil (PTU) is an effective antithyroid medication for Graves' disease but is infrequently associated with antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis (AAV). PTU-induced AAV may occur after prolonged exposure and can present with isolated cutaneous findings, making diagnosis challenging.

Case Presentation:
A 54-year-old woman with Graves' disease treated with PTU for five years presented with a one-month history of progressive palpable purpura involving the upper and lower extremities, followed by polyarthralgia. Laboratory evaluation revealed a positive perinuclear ANCA (p-ANCA) titer of 1:160 (normal reference range < 1:20) with a positive myeloperoxidase (MPO) antibody titer of 1.6 AI (normal reference range < 1.0 AI), and negative proteinase-3 antibodies. Complement levels were normal. Skin biopsy confirmed leukocytoclastic vasculitis. Initial evaluation attributed symptoms to a recently initiated medication, resulting in delayed recognition. After a multidisciplinary review, PTU-induced AAV was suspected, and PTU was discontinued. The patient was treated with systemic corticosteroids, leading to rapid clinical improvement. She subsequently underwent total thyroidectomy for definitive management of Graves' disease. At follow-up a month later, her rash and joint symptoms had resolved.

Conclusion:
This case illustrates late-onset PTU-associated MPO-positive ANCA vasculitis presenting after years of stable therapy. Cutaneous leukocytoclastic vasculitis may be an early manifestation of drug-induced AAV and should prompt evaluation for ANCA positivity in patients receiving PTU. Early recognition, prompt withdrawal of the offending agent, and coordinated multidisciplinary care are critical to preventing progression and achieving favorable outcomes.

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