Clinical importance of antineutrophil cytoplasmic antibody positivity during propylthiouracil treatment

Background: Propylthiouracil (PTU) is the mainstay of antithyroid drug therapy. Previous studies reported antineutrophil cytoplasmic antibody (ANCA)-positive vasculitis in patients treated for Graves' disease. ANCA has been associated with either PTU or to the disease itself. However, this issue has not been investigated in toxic multinodular goitre (TMNG). The aim of this study was to evaluate the frequency of ANCA positivity in both TMNG and Graves' disease patients treated with PTU, and to investigate the clinical importance of this issue. Patients and methods: We studied the presence of ANCA in 46 patients treated with PTU (30 Graves' disease, 16 TMNG). Two years after the discontinuation of PTU, ANCA was re-evaluated in 29 patients (18 Graves' disease, 11 TMNG). Results: By indirect immunofluorescence, 19 of the 46 patients (41.3%) on PTU treatment were ANCA positive [13 of the 30 patients in Graves disease (43.3%), six of the 16 patients in TMNG (37.5%)]. There was no statistically significant difference between Graves' disease and TMNG patients for ANCA positivity (p = 0.362). ANCA positivity was not related to gender, thyroid autoantibodies, alanine aminotransferase, aspartate aminotransferase, neutrophil count and PTU dose. Two years after withdrawal of PTU treatment, 10.3% of patients continued to have positive ANCA (p < 0.0001). Signs and symptoms of vasculitis could not be detected in any of the ANCA-positive patients. Conclusion: Our study suggests that PTU but not Graves' disease itself is the most important factor for ANCA development. The frequency of ANCA positivity is 41.3% in our country which was not different in Graves' disease and TMNG patients. The dose of PTU and ethnic factors are not associated with ANCA positivity. After cessation of PTU, vasculitis did not develop during the 2 years of follow-up despite positive ANCA.