CLINICAL STUDY Prevalence of positive anti-neutrophil cytoplasmic antibody (ANCA) in patients receiving anti-thyroid medication

Objective: Vasculitis is a rare complication of anti-thyroid medications. There are 32 cases of anti-neutrophil cytoplasmic antibody (ANCA)-positive vasculitis in association with anti-thyroid medica-tion reported in the English literature. The objectives of this study were to assess the frequency of positive ANCA in patients on long-term anti-thyroid medication, and to follow patients prospectively from commencement of medication to determine whether they became ANCA-positive after therapy. Design: Prospectively collected cross-sectional study of two groups of patients: (i) who had received long-term (>18 months) anti-thyroid medication, and (ii) newly diagnosed thyrotoxicosis before commencement of anti-thyroid medication attending clinic between 28 April 1998 and 30 September 1998. Data were collected for age, sex, ethnicity, underlying thyroid disease, medication and duration, and symptomatology. Results: Eight of 30 patients on long-term anti-thyroid medication (26.7%) were ANCA-positive. All ANCA-positive patients were female, seven were taking propylthiouracil (PTU) at the time of testing. ANCA-positive patients had taken PTU for a mean 6 S.D. of 7.9 6 10.2 years, compared with 0.8 6 2.2 years in ANCA-negative patients (Mann-Whitney, P < 0.0001). The ten patients with newly diagnose