Antineutrophil Cytoplasmic Antibodies in Patients Treated With Methimazole

Abstract

Introduction: Antithyroid drugs (ATDs) are widely used for the treatment of hyperthyroidism. Most side effects of these medications are mild and emerge within the first months of treatment. In contrast, antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis is a severe adverse event whose occurrence increases with increasing time of treatment. Vasculitis is more frequently associated with propylthiouracil than with methimazole, but the latter has also been related to the occurrence of ANCA and even to clinically manifest vasculitis. Many patients develop ANCA during treatment with methimazole but do not exhibit signs/symptoms of vasculitis. Objective: We previously reported a relatively high frequency (20%) of ANCA in patients exposed to methimazole but none of them exhibited clinical manifestations of vasculitis on that occasion. We continued to follow up these patients with ANCA and report here their evolution after 2 years. Methods: Seventeen patients exposed to methimazole were followed for 2 years after antibodies detection (ANCA). Results: Eight patients had ANCA but had not used methimazole for at least 6 months. During the following 24 months, continuing without ATD, none of the patients developed clinically apparent vasculitis. In the last assessment, five patients no longer had ANCA, while these antibodies persisted in three. Nine patients had ANCA and had been on methimazole for at least 6 months. The medication was not immediately discontinued in these patients when the antibodies were detected. After this detection, treatment with methimazole was continued in these patients for more 3 months (n = 1), 6 months (n = 2), 9 months (n = 1), 12 months (n = 2), 18 months (n = 2), and 24 months (n = 1). During the 2 years of follow-up after the detection of ANCA, none of the 9 patients developed signs/symptoms of vasculitis. In the last assessment, ANCA were negative in two patients who had received methimazole for more 3 and 6 months and who were therefore without receiving the drug for 21 and 18 months, respectively. The other 7 patients remained ANCA positive. Conclusion: Although vasculitis is necessarily associated with the presence of ANCA, the inverse frequency is undefined and appears to be low. Thus, measurement of ANCA would not be recommended in asymptomatic patients during methimazole treatment and immediate discontinuation of this drug, if these antibodies are detected eventually, may not be required. Reference: Antineutrophil cytoplasmic antibodies in patients treated with methimazole: a prospective Brazilian study. Andrade GC, Maia FCP, Mourão GF, Rosario PW, Calsolari MR. Braz J Otorhinolaryngol. 2019; 85:636-41.