Methimazole‐induced ANCA‐associated vasculitis with diffuse alveolar haemorrhage

Antineutrophil cytoplasmic antibody (ANCA)‐associated vasculitis (AAV) caused by methimazole (MMI) is known to be relatively rare; therefore, the optimal therapeutic approach for these cases remains to be established. A 59‐year‐old man who was treated with MMI for a diagnosis of Graves’ disease was referred to our hospital because of progressive haemoptysis. The patient was diagnosed with diffuse alveolar haemorrhage (DAH) secondary to AAV based on increased inflammatory reactions with positive myeloperoxidase‐ANCA in the serum and the results of bronchoalveolar lavage fluid. MMI was suspected as the cause of the AAV; therefore, the administration of MMI was discontinued. Thereafter, the patient’s symptoms as well as chest radiographic abnormalities completely resolved, in conjunction with normalization of the serum ANCA level. Our experience with this case suggests that DAH secondary to AAV caused by MMI may improve with discontinuation of the offending drug alone, with no other treatment.