Subcarinal Mass: An Unusual Presentation of Granulomatosis With Polyangiitis

BACKGROUND Granulomatosis with polyangiitis (GPA) is a small-to-medium vessel necrotizing vasculitis that affects multiple organ systems. It commonly manifests as glomerulonephritis and inflammation involving the respiratory tract. Rarely, ocular, cutaneous, neurological, and musculoskeletal manifestations occur. Mass lesions are uncommon in GPA. Our patient had a subcarinal mass and was diagnosed with GPA. In our literature review, we identified several reports of mediastinal masses; however, no specific cases of subcarinal masses were found. CASE REPORT A 22-year-old woman presented with syncope, chest pain, and weight loss. Imaging revealed a subcarinal mass. This was concerning for lymphoma or histoplasmosis. Extensive testing ensued, while treatment for histoplasmosis was initiated. Workup included a mediastinal mass biopsy that revealed granulomatous inflammation. While testing was ongoing, she developed purpuric rashes on her lower extremities and hematuria, and was subsequently found to have proteinuria of 274 mg per 24 hours. Autoimmune testing was initiated, and she was found to be positive for serine protease-3 antibody and antineutrophil cytoplasmic antibody (ANCA) indirect immunofluorescence assay with a cytoplasmic ANCA pattern and 1: 320 titer. The latter is highly specific for GPA and, along with granulomatous inflammation and clinical findings, confirmed the diagnosis. She was treated with prednisone and rituximab and had significant clinical improvement at the time of discharge. CONCLUSIONS Subcarinal masses are commonly caused by malignancies and infections. This case details an unusual presentation of GPA as a subcarinal mass. It highlights the importance of considering GPA as a possible diagnosis for patients with constitutional symptoms, mediastinal mass, and necrotizing granulomatous inflammation on pathology.