Pulmonary nodules in a case of microscopic polyangiitis: a case report and review of the literature

BACKGROUND: Microscopic polyangiitis (MPA) is a type of small-vessel vasculitis that can lead to organ damage, primarily affecting the kidneys and lungs. CASE PRESENTATION: We described a 31-year-old female of East Asian ethnicity exhibiting fever, reduced appetite, fatigue, proteinuria, hematuria, and renal function impairment. Renal biopsy, along with the detection of anti-MPO (myeloperoxidase)-ANCA (anti-neutrophil cytoplasmic antibodies) and anti-GBM (glomerular basement membrane) antibodies, confirmed the diagnosis of ANCA-associated small-vessel vasculitis with renal injury, specifically Type III crescentic glomerulonephritis, namely MPA. Concurrently, the chest computed tomography (CT) of this patient revealed pulmonary nodules, raising initial suspicions of lung cancer. However, following a regimen of steroids and cyclophosphamide, the patient experienced a rapid improvement in symptoms, and a significant reduction in the size of the pulmonary nodules, ultimately avoiding the resection surgery. CONCLUSIONS: This case highlights the critical need for accurate differentiation of pulmonary nodules in MPA patients, ensuring timely and appropriate treatment.