Difficulties in the differential diagnosis of kidney injury in a patient with infective endocarditis associated with antineutrophil cytoplasmic antibodies

: Infective endocarditis (IE) may be accompanied by the production of a broad spectrum of autoantibodies, including antineutrophil cytoplasmic antibodies (ANCA). ANCA detection creates difficulties in the differential diagnosis of IE, especially in relation to kidney injury, the determination of the mechanism of which is important for choosing a treatment policy and estimating a prognosis. The paper describes a clinical case of a 57-year-old man who was found to have higher proteinase-3 (PR-3) ANCA titers along with the symptoms of anemia, purpura, and kidney injury during his hospitalization; echocardiography revealed vegetation on the aortic valve. IE was diagnosed; 2-week antibiotic therapy was ineffective; there was progressive aortic insufficiency necessitating aortic valve replacement. In the postoperative period, there was progression of renal failure and higher PR-3 ANCA titers, which made it possible to regard kidney injury as a manifestation of ANCA-associated glomerulonephritis. Intensive immunosuppressive therapy with intravenous and oral prednisolone was initiated, which showed positive effects in reducing proteinuria, erythrocyturia, serum creatinine levels, and simultaneously PR-3 ANCA titers. The paper gives the data available in the literature on the frequency of an association of IE with ANCA, the clinical features, diagnostic criteria, and treatment approaches. It discusses the mechanisms of ANCA formation in patients with IE.