Abstract Background Granulomatosis with polyangiitis (GPA) is an antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis characterized by necrotizing granulomatous inflammation of small- to medium-sized vessels, predominantly affecting the respiratory tract and kidneys. Cavitary pulmonary lesions occur in approximately one-fourth of cases, yet isolated pulmonary presentations without ear-nose-throat or renal involvement are rare, accounting for less than 10%. Such cases may mimic infection or malignancy, delaying diagnosis. Early recognition and immunosuppressive therapy are essential to prevent irreversible organ damage. Case Report A 33-year-old Caucasian male presented with four days of hemoptysis and one month of bilateral ankle and knee pain, fever, chills, and unintentional weight loss. He denied nasal, renal, or urinary symptoms. Chest radiography demonstrated a large peripheral cavitary lesion in the superior right lower lobe and a small opacity in the left upper lobe. Computed tomography revealed a thick-walled 7 × 8×8 cm right lower lobe cavity, initially suspicious for infection. Extensive infectious workup—including bacterial, mycobacterial, viral, and fungal studies—was negative. Autoimmune testing showed positive cytoplasmic ANCA (1:80) and elevated PR3 antibody (33.0 U/mL), consistent with GPA; other serologies were negative. Bronchoscopy with lavage and transbronchial biopsy were performed; histopathology lacked necrotizing granulomas but revealed nonspecific inflammation. Given the clinical and serologic correlation, GPA was diagnosed. The patient received high-dose corticosteroids, rituximab, and trimethoprim-sulfamethoxazole for Pneumocystis prophylaxis, resulting in marked improvement. He was discharged with rheumatology and pulmonology follow-up. Discussion This case illustrates an atypical presentation of GPA with isolated pulmonary involvement and a large cavitary lesion. The diagnostic challenge lies in distinguishing GPA from infectious or neoplastic etiologies, particularly when biopsy is nondiagnostic. C-ANCA directed against PR3 is highly specific for GPA and correlates with relapse risk. Modern management emphasizes early immunosuppression with corticosteroids and rituximab, which has demonstrated non-inferiority to cyclophosphamide in the RAVE and RITUXVAS trials, and superiority for relapse prevention in the MAINRITSAN trial. PR3-positive patients, like ours, require long-term surveillance given higher relapse propensity. Conclusion Isolated pulmonary GPA is an uncommon but important diagnostic consideration in cavitary lung disease. This case underscores the importance of maintaining a broad differential for hemoptysis, utilizing serologic markers when histopathology is inconclusive, and initiating prompt immunosuppressive therapy to prevent progression and relapse. This abstract is funded by: n/a
Ahmed et al. (2026) studied this question.