Antineutrophil cytoplasmic antibody positive alveolar haemorrhage during propylthiouracil therapy for hyperthyroidism

Recently, propylthiouracil (PTU) has been thought to be one of the possible causes of antineutrophil cytoplasmic antibody (ANCA)-associated small vessel vasculitis syndrome, resulting in glomerulonephritis and, infrequently, diffuse alveolar haemorrhage (DAH). The mechanism of ANCA-positive vasculitis during PTU therapy is still unknown. Herein, we describe the case of a 59-year-old woman who developed myeloperoxidase (MPO)- and proteinase 3 (PR3)-ANCA positive DAH, without any other organ system involvement, during PTU therapy. Diminution and discontinuation of PTU resulted in a positive response. To our knowledge, this is the first documentation of both MPO- and PR3-ANCA-positive DAH, without systemic manifestations, developing during PTU therapy.