Clinical Characteristics of Myeloperoxidase Antineutrophil Cytoplasmic Antibody-Associated Vasculitis Caused by Antithyroid Drugs

CONTEXT: The clinical characteristics of myeloperoxidase antineutrophil cytoplasmic antibody (MPO-ANCA)-associated vasculitis caused by antithyroid drugs are still unclear because most reports describe only a small number of patients. OBJECTIVE: The objective was to analyze a large number of patients with MPO-ANCA-associated vasculitis to determine the time of onset, the drug and dose taken, the clinical symptoms, the relationship between the clinical symptoms and the MPO-ANCA titer, and the incidence. DESIGN: We analyzed 92 patients in whom the adverse reaction of MPO-ANCA-associated vasculitis was reported to Chugai Pharmaceutical, a company that markets antithyroid drugs. RESULTS: Of the 92 patients, 41 (44.6%) had single-organ failure, 32 (34.8%) had two-organ failure, 13 (14.1%), had three-organ failure, and two (2.2%) had four-organ failure. The number of organs involved was unknown in the other four patients (4.3%). The median time of onset was 42 months (range, 1-372 months) after starting drug treatment. The median dose at onset of MPO-ANCA-associated vasculitis was 15 mg/d (range, 2.5-45 mg/d) for methimazole and 200 mg/d (50-450 mg/d) for propylthiouracil. The severity and number of organs involved were not correlated with the MPO-ANCA titer. The incidence was between 0.53 and 0.79 patients per 10,000, and the ratio of the estimated incidences for methimazole and propylthiouracil was 1:39.2. CONCLUSIONS: The time of onset of MPO-ANCA-associated vasculitis and the dose at onset varied. The severity and number of organs involved were not correlated with the MPO-ANCA titer, indicating a need for vigilance even when the MPO-ANCA titer is only weakly positive.