Iatrogenic antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) is not exceptional. Many cases of small vessel vasculitis induced by anti-thyroid drugs (ATD), mainly propylthiouracil (PTU), have been reported. We present a case of AAV related to another ATD: benzylthiouracil (BTU) and review the literature. An 84-year-old man with a 4-year history of multinodular goitre with hyperthyroidism was treated with BTU. He presented an acute syndrome with weakness, fever, epigastric pain and abdominal distension. Lactate and lipase tests were normal. An abdominal scan showed a thrombosis of the splenic artery with splenic infarction. We excluded a hypothesis of associated embolic aetiology: atrial fibrillation, atrial myxoma, intraventricular thrombus or artery aneurysm. Exploration of a possible prothrombotic state (complete blood count, haemostasis tests, activated protein C resistance, factor V Leiden, protein C, S, antithrombin III) gave normal results. Tests for antinuclear antibodies (ANA) and antiphospholipid antibodies (APL) were negative. However, testing for p-ANCA, with antimyeloperoxidase (MPO) specificity, was positive: 120.6 CU (N<20.0). We did not find other systemic manifestations, except a non-specific kidney failure. BTU was discontinued without steroids or immune-modulating drugs. Subsequently, symptoms disappeared progressively and titres of ANCA fell until normalization, 4 months later. Many patients treated with BTU present a high prevalence of ANCA, mainly, but not exclusively, directed against MPO. Vasculitis, however, remains an uncommon complication. The mechanism of this anomaly remains to be elucidated. Some studies suggest the possibility of an autoimmune reaction initiated by drug bioactivation mediated by neutrophil-derived MPO. The present observation is particular because the involved drug was BTU and clinical expression was unusual.
Learning points:
ANCA-associated vasculitis related to anti-thyroid drugs is not exceptional, particularly in patients receiving long-term therapy with thioamides.Clinical manifestations are highly variable.Treatment consists firstly of stopping the anti-thyroid drug. Introduction of steroids and/or immunosuppressive therapy depends on the severity of organic impairments. Prognosis is less severe than primary ANCA vasculitis.