Antineutrophil cytoplasmic antibody-associated vasculitis superimposed on infection-related glomerulonephritis secondary to pulmonary Mycobacterium avium complex infection

A 73-year-old woman was diagnosed with pulmonary Mycobacterium avium complex (MAC) infection and received no treatment. Disease progression was evident one year later with the development of myeloperoxidase-antineutrophil cytoplasmic antibody (ANCA) titers and systemic symptoms of a fever, polyarthritis, purpura, and rapidly progressive glomerulonephritis. Her symptoms did not improve with antibiotic treatment. A renal biopsy revealed crescentic glomerulonephritis with immunodeposition. According to these findings, she was diagnosed with ANCA-associated vasculitis (AAV) superimposed on infection-related glomerulonephritis (IRGN). Although there was a risk of aggravating an underlying infection, the combination therapy of corticosteroid and antibiotics improved AAV, IRGN, and even the lung radiological findings. To the best of our knowledge, this is the first case of AAV and IRGN secondary to pulmonary MAC infection.