Prevalence of antineutrophil cytoplasmic antibodies during treatment with benzylthiouracil.

Background: Drug induced antineutrophil cytoplasmic antibodies (ANCA) associated vasculitis is a rare complication associated especially with propylthiouracil (PTU). Prevalence of ANCA in patients receiving PTU is well established. Few cases of vasculitis were also reported with benzylthiouracil (BTU). The objective of this study is to clarify the prevalence of ANCA in patients receiving BTU.

Methods: ANCA were investigated by indirect immunofluoresence and enzyme linked immunosorbant assay in 159 patients with Graves' disease (86 untreated and 73 treated with BTU).

Results: ANCA were positive in three (3.5%) untreated patients and 27 (37%) treated ones. Titres of ANCA varied between 1:20 and 1:200. There was a significant association between BTU treatment and ANCA (p<0.001). ANCA were directed against myeloperoxidase (MPO) in 28 (93.3%) patients. Median treatment duration was 24 months (ranges 0.5 to 144 months). There was no significant association between treatment duration and ANCA. Vasculitis was found in two (2.7%) treated patients. One patient has developed isolated cutaneous vasculitis and the other one a pulmonary vasculitis with diffuse alveolar haemorrhage.

Conclusion: BTU therapy is characterised by a high prevalence of ANCA mainly but not exclusively directed against MPO. However, vasculitis remains a rare complication.