A Case of Bartonella henselae Infection-Related Glomerulonephritis and Endocarditis with Negative Blood Culture Mimicking PR3-ANCA-Associated Vasculitis

Introduction: A case of Bartonella henselae infection-related glomerulonephritis and endocarditis with negative blood culture mimicking PR3-ANCA associated vasculitis. Case Description: A 70-year-old female with a history of aortic stenosis was admitted to our hospital because of fever and fatigue. The laboratory data revealed cytopenia and an elevated creatinine level from 0.50 mg/dL to 0.97 mg/dL with hematuria and urinary protein of 0.5 g/gCr. Immunological tests revealed positive PR3-ANCA (52 U/mL), rheumatoid factor (90.4 IU/mL), and reduced C3 (71.7 mg/dL). Blood culture was negative. Renal biopsy revealed endocapillary proliferation and endothelial cell swelling without crescent formation. Immunofluorescence showed the deposition of IgM and C3c on the capillary wall. The pathological diagnosis was consistent with IRGN. Considering the habit of keeping 30 wild cats, blood polymerase chain reaction (PCR) testing was performed, which was positive for B. henselae. Echocardiography and brain MRI revealed newly noted aortic valve regurgitation and subacute cerebral infarction. The diagnoses of B. henselae IRGN and IE were confirmed. We initiated rifampicin and doxycycline, which were eventually changed to gentamycin and minocycline due to adverse events of nausea and vomiting. Cytopenia, renal function, and urinalysis results improved. Subsequently, the patient underwent aortic valve replacement, and the excised valve was positive for B. henselae PCR. Discussion: The differential diagnosis of PR-3 ANCA-positive IRGN and AAV is often challenging, particularly in cases with negative blood or tissue cultures. B. henselae cannot be easily isolated from clinical specimens owing to its fastidious nature. In the present case, PCR testing and renal biopsy were essential for confirming B. henselae infection and treatment decisions.