A Case of Granulomatosis with Polyangiitis Masquerading as Tuberculosis.

Granulomatosis with polyangiitis (GPA) is a medium- and small-vessel necrotizing vasculitis that affects the upper and lower respiratory tracts, resulting in symptomatic and radiographic similarities with pulmonary tuberculosis (TB). We discuss the case of a 45-year-old previously healthy male who recently immigrated from India that presented after three weeks of rifampin, isoniazid, pyrazinamide, and ethambutol (RIPE) therapy for presumed TB prior to receiving the GPA diagnosis. Previous admission to a community hospital yielded negative Mycobacterium tuberculosis polymerase chain reaction (MTB PCR) and acid-fast bacillus (AFB) sputum cultures, prompting repeat testing and broad autoimmune/infectious workup. Chest computed tomography redemonstrated cavitary lesions with interval enlargement. Dermatopathology of bilateral lower extremity palpable purpura that erupted during admission demonstrated findings consistent with small-vessel vasculitis. Cytoplasmic-antineutrophil cytoplasmic antibodies was positive (1:80), and serine proteinase-3 IgG was 546 AU/mL (ref<19 AU/mL). Bronchoalveolar lavage samples produced a negative MTB PCR and AFB culture. This case highlights the importance of differentiating clinically similar diseases that can be symptomatically detrimental and require potentially competing therapeutics. Some evidence, including in vitro studies and acute care patients, suggests low risk of harm to initiate GPA treatment with possible concomitant TB. We hope this case informs providers to avoid diagnostic bias and consider early steroid treatment for patients suspicious of GPA in the absence of an unequivocal TB diagnosis.