Granulomatosis With Polyangiitis (GPA) Mimicking Metastatic Malignancy.

Granulomatosis with polyangiitis is a rare vasculitis characterized by necrotizing granulomatous inflammation affecting small blood vessels. It often presents with pulmonary masses and nodules, mimicking malignancy in imaging studies. Distinguishing granulomatosis with polyangiitis from cancer is crucial due to differing treatment approaches and prognoses. We describe a 54-year-old male with granulomatosis with polyangiitis presenting with headache, bilateral ear discharge, cough, and weight loss. Imaging revealed metabolically active lesions in the lungs and nasopharynx, initially suggestive of metastatic malignancy. Biopsies from the lung and nasopharyngeal lesions showed necrotizing granulomatous vasculitis, which was suggestive of granulomatosis with polyangiitis. Serological testing was positive for cytoplasmic antineutrophil cytoplasmic antibodies (c-ANCA) with elevated proteinase 3 (PR3) antibodies. This case underscores the diagnostic challenges of granulomatosis with polyangiitis, which can mimic malignancy radiologically. Early recognition and treatment initiation are pivotal in improving patient outcomes and preventing organ damage in granulomatosis with polyangiitis.