Propylthiouracil (PTU) is a commonly used medication for the treatment of hyperthyroidism. PTU is known to cause different adverse reactions including autoimmune syndromes. PTU-induced autoimmune syndromes can be classified into drug-induced lupus or drug-induced vasculitis. Differential diagnoses could be very challenging. PTU-induced vasculitis is more common than PTU-induced lupus, and has a higher risk of morbidity and mortality. Usually it is limited to the skin in a form of cutaneous leukocytoclastic vasculitis, but may also affect organs including kidneys and lungs. Discontinuation of PTU should be a first step in the treatment and could lead to complete resolution of symptoms. Typically, lesions resolve spontaneously within 2-4 weeks, but chronic or recurrent disease may occur in up to 10% of patients. In cases without improvement after drug discontinuation, cases refractory to glucocorticosteroids, with necrotizing skin lesions or extracutaneous organ involvement referral to rheumatologist for more aggressive immunosuppressive treatment is indicated. Optimal duration of immunosuppressive therapy is unknown, but it is reasonable to gradually taper mediations and monitor clinical response. Frequent monitoring for side effects is mandatory for patients on PTU therapy. Treatment should be stopped immediately, if patient develops any of autoimmune syndromes. An accurate and prompt diagnosis is essential, because it determines further management. We report a rare case of antineutrophil cytoplasm antibody-negative cutaneous small vessel vasculitis as a result of longstanding exposure to PTU.
Keywords: ANCA-negative; Propylthiouracil; cutaneous vasculitis; drug-induced vasculitis.