Granulomatosis With Polyangiitis Presenting as Pulmonary Masses With Coexisting Infection: A Diagnostic Challenge Leading to Life-Threatening Pulmonary-Renal Syndrome.

Granulomatosis with polyangiitis (GPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis that can mimic infection and malignancy, posing a significant diagnostic challenge. We report the case of a 39-year-old male smoker with a strong family history of lung cancer who presented with fever, weight loss, dyspnea, and hemoptysis. Initial evaluation supported infection, with sputum cultures positive for Pseudomonas aeruginosa and Haemophilus influenzae. Imaging later revealed pulmonary masses suspicious for malignancy. The patient subsequently deteriorated with massive hemoptysis and acute kidney injury, requiring ICU admission, mechanical ventilation, blood transfusion, and dialysis. Further investigations demonstrated proteinase 3-ANCA positivity and diffuse alveolar hemorrhage on bronchoalveolar lavage, confirming GPA. Treatment with pulse corticosteroids, IV cyclophosphamide, and plasma exchange resulted in marked clinical recovery. This case underscores the significant diagnostic challenge posed by the overlap between infection, malignancy, and ANCA-associated vasculitis, highlighting the importance of early recognition and timely initiation of immunosuppressive therapy.