Case Presentation: A 64-year-old male with past medical history of hypertension (HTN), hyperlipidemia, coronary artery disease, and end stage renal disease, secondary to HTN, on hemodialysis presented with a 3-day history of nonproductive cough and malaise with no other associated symptoms. On admission vital signs were within normal limits; physical exam revealed decreased breath sounds at bases, asthenia, anasarca, and new grade 2/6 non-radiating diastolic murmur in the aortic area. Initial blood investigation revealed total leukocyte count of 13000/μL and creatinine of 4.4mg/dl. Chest x-ray revealed bilateral pleural effusion and right upper lobe infiltrate. The initial diagnosis of health care associated pneumonia was made and Vancomycin and Piperacillin/Tazobactam were started. Because of constitutional symptoms with pulmonary and renal involvement, ANCA panel was sent and later came back as weakly positive: His cytoplasmic anti-neutrophil cytoplasmic antibody (C-ANCA) titers were 1:20 and anti-proteinase-3 (PR3) was 12.4. While deciding, whether to start immunosuppressive therapy, blood cultures, drawn on the day of admission, grew Staphylococcus epidermidis in both the aerobic and anaerobic bottles. Further work up with transthoracic echocardiogram (TTE) revealed vegetative aortic valve with moderate aortic insufficiency. Antibiotics were changed to Vancomycin and Gentamycin to treat for infective endocarditis and patient recovered fully.

Discussion: SBE can rarely manifest with features of ANCA-associated vasculitides (AAV). ANCAs directed against PR3 or myeloperoxidase are important diagnostic markers for AAV. However, it is predicted that the chronic infectious process plays a central role in the formation of ANCA through polyclonal B-cell activiation1 and microembolism affecting circulating immune complexes on the vascular endothelium2. Differentiating SBE and AAV is challenging, because they often share similar clinical manifestations such as fever, glomerulonephritis and cutaneous lesions2. The diagnostic effort is further challenged if the murmur is missed or if the patient has a culture negative SBE with positive ANCA. Fortunately, our patient’s culture came back positive, and his murmur was further evaluated with TTE, and the diagnosis of SBE was made. The misdiagnosis of an infectious disease as AAV and subsequent inappropriate immunosuppression therapy can disseminate infection and have detrimental consequences. Therefore, in patient with presumed AAV, diagnosis of SBE should be considered and ruled out3.

Conclusions: ANCA titers can be elevated in both infectious and non- infectious process and these results should be interpreted with caution. The misdiagnosis of an infectious disease as AAV and the administration of immunosuppressive therapy could worsen the infection and lead to disastrous consequences. Clinical presentations and diagnostic criteria need to be considered to differentiate various etiologies.