A grave complication: propylthiouracil-induced antineutrophil cytoplasmic antibody-associated vasculitis.

Propylthiouracil (PTU) is a commonly used antithyroid agent for the treatment of hyperthyroidism. While generally well tolerated, it has been associated with serious adverse effects, including agranulocytosis, hepatotoxicity, and, more rarely, antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. We present a case of a 58-year-old woman, known for Graves disease on 5 years of PTU treatment, who developed a hypertensive emergency and progressive renal dysfunction, initially attributed to nonsteroidal anti-inflammatory drug use. Further laboratory evaluation and kidney biopsy confirmed a diagnosis of ANCA-associated vasculitis likely induced by long-term PTU treatment. PTU was discontinued, and a prednisone taper was initiated, resulting in improvement in renal function. Following PTU discontinuation, corticosteroid therapy, and blood pressure management, the patient entered a euthyroid state with improved renal function.