Frequency of appearance of myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA) in Graves' disease patients treated with propylthiouracil and the relationship between MPO-ANCA and clinical manifestations

OBJECTIVE Myeloperoxidase antineutrophil cytoplasmic antibody (MPO-ANCA)-positive vasculitis has been reported in patients with Graves' disease who were treated with propylthiouracil (PTU). The appearance of MPO-ANCA in these cases was suspected of being related to PTU because the titres of MPO-ANCA decreased when PTU was stopped. Nevertheless, there have been no studies on the temporal relationship between the appearance of MPO-ANCA and vasculitis during PTU therapy, or on the incidence of MPO-ANCA in untreated Graves' disease patients. Therefore, we sought to address these parameters in patients with Graves' disease. PATIENTS We investigated 102 untreated patients with hyperthyroidism due to Graves' disease for the presence of MPO-ANCA, and for the development vasculitis after starting PTU therapy. Twenty-nine of them were later excluded because of adverse effects of PTU or because the observation period was less than 3 months. The remaining 73 patients (55 women and 18 men), all of whom were examined for more than 3 months, were adopted as the subjects of the investigation. The median observation period was 23.6 months (range: 3-37 months). MEASUREMENTS MPO-ANCA was measured at intervals of 2-6 months. RESULTS Before treatment, the MPO-ANCA titres of all 102 untreated Graves' disease patients were within the reference range (below 10 U/ml). Three (4.1%) of the 73 patients were positive for MPO-ANCA at 13, 16 and 17 months, respectively, after the start of PTU therapy. In two of them, the MPO-ANCA titres transiently increased to 12.8 and 15.0 U/ml, respectively, despite continued PTU therapy, but no vasculitic disorders developed. In the third patient, the MPO-ANCA titre increased to 204 U/ml and she developed a higher fever, oral ulcers and polyarthralgia, but the symptoms resolved 2 weeks after stopping PTU therapy, and the MPO-ANCA titre decreased to 20.7 U/ml by 4 months after discontinuing PTU. CONCLUSIONS PTU therapy may be related to the appearance of MPO-ANCA, but MPO-ANCA does not appear to be closely related to vasculitis.