BACKGROUND: Granulomatosis with polyangiitis (GPA) relapse can complicate the differential diagnosis of pulmonary lesions.

CASE REPORT: A 70-year-old male smoker with GPA and emphysema presented with dyspnea, dry cough, and a right upper lobe pulmonary ground-glass opacity that persisted despite antibiotics. A trans-bronchial biopsy did not reveal active vasculitis, malignancy, or infection. He was treated for presumed GPA relapse based on pulmonary manifestations, renal failure, and elevated PR3-ANCA. Later, hematuria led to the cystoscopic discovery of a bladder wall lesion, which was diagnosed as micropapillary urothelial carcinoma not involving the muscularis propria. The patient developed an increasing pulmonary infiltrate with a new solid component, satellite lesions, and regional lymphadenopathy. A right upper lobe wedge resection showed metastatic urothelial carcinoma.

CONCLUSIONS: The simultaneous presentation of a pulmonary lesion and GPA relapse is a diagnostic challenge. The differential diagnosis should include the rare possibility of metastatic urothelial carcinoma, regardless of how the lesion appears radiographically.

Keywords: Bronchoscopy, Biopsy, Aged, 80 and over, Carcinoma, Transitional Cell - secondary, Cystoscopy, Diagnosis, Differential, Granulomatosis with Polyangiitis - diagnosis, Lung Neoplasms - secondary, Tomography, X-Ray Computed, Urinary Bladder Neoplasms - pathology