Culture-negative subacute bacterial endocarditis masquerades as granulomatosis with polyangiitis (Wegener’s granulomatosis) involving both the kidney and lung

BACKGROUND Subacute bacterial endocarditis (SBE) occasionally exhibits positive cytoplasmic anti-neutrophil cytoplasmic antibody (c-ANCA) of the anti-proteinase-3 (PR-3) type. Clinically, it mimics ANCA-associated vasculitis, such as Wegener's disease with glomerulonephritis. Lung abscesses are the most common manifestation of lung involvement. We herein report a case of culture-negative SBE strongly c-ANCA/PR3-positive accompanied by pulmonary involvement and glomerulonephritis. In this case, we took biopsies of both the lung and kidney, although renal biopsy is usually preferred over lung biopsy. The lung biopsy showed severe alveolar capillaritis, suggesting vasculitis consistent with polyangiitis. The renal biopsy revealed glomerulonephritis with a membranoproliferative pattern. To our knowledge, this is the first such reported case. CASE PRESENTATION A 68-year-old Chinese male patient presented to our hospital with a fever, cough, chest pain, and recurrent peripheral edema. He had a past medical history significant for treated schistosomiasis 20 years previously. Physical examination revealed palpable purpura, mild hypertension, hepatosplenomegaly, and a holosystolic cardiac murmur (Levine 2/6). Echocardiography showed tricuspid valve vegetations with moderate to severe regurgitation. Serum c-ANCA/PR3 and cryoglobulin were strongly positive. Renal biopsy results indicated membranoproliferative glomerulonephritis with several crescents. Chest CT revealed multiple intraparenchymal and subpleural nodules, and lung biopsy showed polyangiitis. The patient's ANCA titers, glomerulonephritis, and pulmonary injury all resolved after antibiotic therapy. CONCLUSION SBE may present with positive c-ANCA/PR3, multiple pulmonary nodules, pulmonary polyangiitis, and glomerulonephritis clinically mimicking granulomatosis with polyangiitis (Wegener's granulomatosis).