Multiple Cavitary Lung Lesions in ANCA-Negative Small Vessel Vasculitis: A Case Report

Multiple cavitary lung lesions present a diagnostic challenge, with a broad differential diagnosis, including infectious, malignant, and autoimmune etiologies. ANCA-associated vasculitis (AAV), particularly in its seronegative form, is a rare yet important cause that is frequently overlooked, as pulmonary involvement is uncommon and its manifestations can closely mimic infection or malignancy. We report a case of a 30-year-old male who presented with a three-week history of dyspnea and hemoptysis, and a background of membranoproliferative glomerulonephritis confirmed by renal biopsy three months prior, consistent with pauci-immune glomerulonephritis. Chest radiography and contrast-enhanced CT revealed multiple bilateral cavitary lung lesions with air-fluid levels, micronodules, and centrilobular ground-glass opacities. Extensive infectious workup, including sputum and bronchoalveolar lavage cultures, acid-fast bacilli smear, GeneXpert, and fungal studies, was negative. Cytological examination excluded malignancy. Both p-ANCA and c-ANCA were negative. Based on the 2022 ACR/EULAR classification criteria, a diagnosis of ANCA-negative microscopic polyangiitis (MPA) was established, with a total score of +6 derived from imaging findings consistent with interstitial lung disease and histopathological evidence of pauci-immune glomerulonephritis in a prior renal biopsy. Immunosuppressive therapy with methylprednisolone and mycophenolate sodium was initiated, resulting in complete radiological resolution of all cavitary lesions within two months. This case highlights that cavitary lung lesions may represent a rare pulmonary manifestation of ANCA-negative MPA. A negative ANCA result should not exclude vasculitis when clinical suspicion is high, and tissue biopsy remains essential for definitive diagnosis in atypical presentations.