Objective: To report a potentially important limitation of antineutrophil cytoplasmic antibody (ANCA) testing: positive results in patients with subacute bacterial endocarditis (SBE).
Methods: We describe 3 patients with SBE who presented with features mimicking ANCA-associated vasculitis (AAV) and positive findings on tests for cytoplasmic ANCA (cANCA) by indirect immunofluorescence and for anti-proteinase 3 (anti-PR3)antibodies by antigen-specific enzyme-linked immunosorbent assay (ELISA). We also reviewed the published literature describing infectious diseases with (misinterpreted) positive ANCA results through a Medline search of English-language articles published between 1966 and January 1999. These previously reported cases were reinterpreted using an ANCA scoring system that combines the findings of immunofluorescence and antigen-specific ELISA testing.
Results: We are now aware of a total of 7 cases of SBE with positive cANCA and anti-PR3 antibodies. We are not aware of any cases of SBE associated with antimyeloperoxidase/perinuclear ANCA. Clinical manifestations mimicking AAV included glomerulonephritis, purpura, epistaxis, or sinus symptoms in 6 of the patients. Streptococcal species were identified in 5 patients, and cardiac valvular abnormalities were demonstrated in 6. All patients except 1, who died of a complication of SBE, recovered with antibiotic therapy.
Conclusion: Findings of tests for anti-PR3/ cANCA antibodies may be positive in patients with SBE. When encountering ANCA positivity in patients suspected of having systemic vasculitis, physicians should take appropriate steps to rule out infectious diseases, including SBE, before committing the patient to long-term, aggressive immunosuppressive therapy.