ANCA positivity in the case of acute bacterial endocarditis

Background: The case of ANCA positivity in an individual with bacterial endocarditis demonstrates the importance of thorough testing and labs prior to treatment. This case draws attention to a diagnostic conflict, as starting treatment on immunosuppressants, as would be the standard therapy for ANCA-associated vasculitis (AAV), could exacerbate the bacterial endocarditis and carry severe consequences. In this case of glomerulonephritis and associated endocarditis, the patient presented with several symptoms which mimicked AAV. Thus, it is important for providers to include cultures in routine assessments of ANCA-positive cases to allow for thorough evaluation and appropriate therapy.

Case information: A 60-year-old morbidly obese male presented for right knee pain. His medical history includes hypertension, congestive heart failure (CHF), osteoarthritis, atrial fibrillation, and stage IV chronic kidney disease (CKD). The patient denied history of smoking, drugs, or alcohol use. He has no family history of autoimmune disease. Upon evaluation, the patient was found to have a deep vein thrombosis (DVT) with leg pain, as well as paroxysmal atrial fibrillation. He was started on Coumadin for anticoagulation therapy. During his hospital stay, his creatinine levels climbed from 2.0 mg/dL to 6.3 mg/dL and was given a preliminary diagnosis of acute renal failure on top of his preexisting CKD. His renal decline prompted a kidney biopsy, which revealed focal necrotizing and crescentic glomerulonephritis with C3 dominant deposition. Urinalysis showed proteinuria and was positive for active urinary sediment. Bloodwork was remarkable for MPO-ANCA positivity (MPO-ANCA 1:640). Transesophageal echocardiogram (TEE) and blood culture revealed an aortic valve vegetation positive for methicillin-sensitive staphylococcus aureus (MSSA), and the patient was started on broad-spectrum antibiotic therapy.

Conclusions: The details of this case prompt reflection on the diagnostic steps taken by providers when presented with an ANCA-positive patient. The standard protocol taken in the treatment of ANCA vasculitis differs tremendously from and could even have devastating consequences in the case of infectious endocarditis. Therefore, careful evaluation for bacterial endocarditis in the case of ANCA positivity should be incorporated into the diagnostic process. Most of the current literature represents cases of c-ANCA positivity in subacute infectious endocarditis (IE), often with Streptococcus viridans responsible. This case is unique in that the patient was positive for MPO-ANCA and not PR3 and the causative organism was MSSA. While several cases of MSSA IE with ANCA positivity have been reported, this combination of MSSA endocarditis and isolated MPO-ANCA positivity has only been represented one other time in the literature to our knowledge.