Graves' Disease with Myeloperoxidase Antineutrophil Cytoplasmic Antibody-associated Vasculitis Caused by Antithyroid Drugs —Two Case Reports—

Abstract

Case 1 : A 49-year-old woman with Graves' disease received 20 mg of methimazole (MMI) daily for 1 month and was admitted to our hospital with diffuse arthralgia after the discontinuation of MMI. Her clinical symptom improved within a week. Her symptom subsided a month later with improvement in her myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA) titer. Two months later, the titer decreased to within the reference range. She was diagnosed with MPO-ANCA-associated vasculitis secondary to antithyroid drug use on the basis of her clinical course and laboratory investigations.

Case 2 : A 64-year-old woman with Graves' disease who received propylthiouracil for 10 years presented with an increased white blood cell count and serum C-reactive protein level, as well as purpura, arthralgia, hematuria, and proteinuria. She was diagnosed with MPO-ANCA-associated vasculitis on the basis of a high MPO-ANCA titer and clinical symptoms suggestive of vasculitis. She showed a prolonged activated partial thromboplastin time and elevated serum levels of lupus anticoagulant and was considered an asymptomatic antiphospholipid antibody carrier. Total thyroidectomy was performed after discontinuation of the antithyroid drug. Her clinical symptoms subsided with gradual improvement in her MPO-ANCA titer within a month postoperatively. Her MPO-ANCA titer improved and serum levels of lupus anticoagulant decreased to the normal range 16 months later. We diagnosed MPO-ANCA-associated vasculitis secondary to antithyroid drug use in an asymptomatic antiphospholipid antibody carrier.