A Cat and a "Full House"

Introduction: In a patient with constitutional symptoms, positive ANA serologies, and hypocomplementemia, immune complex glomerulonephritis (GN) often suggests lupus nephritis. However, Bartonella endocarditis can mimic this presentation. We detail the case of a 34-year-old man with history of pulmonary valve replacement and cat bite with acute kidney injury (AKI) due to Bartonella endocarditis-related GN. Case Description: The patient initially presented with upper respiratory symptoms, diarrhea, and AKI, attributed to hypovolemia and NSAID use. AKI worsened despite resolution of symptoms. Further workup revealed elevated rheumatoid factor, positive Epstein-Barr Virus (EBV) IgM, normal complement levels, and negative infectious workup. Kidney biopsy was consistent with IgA nephropathy. Post-discharge, he developed a pruritic rash, assumed to be IgA vasculitis. Twelve days later, he returned with a new pulmonic regurgitation murmur, weight loss, nocturnal fevers, and heart failure symptoms. Both transthoracic and transesophageal echocardiograms were negative for vegetations, but Bartonella IgG titers were elevated. Glucocorticoids resolved symptoms and AKI temporarily, but they recurred post-tapering, prompting transfer to our institution. Repeat serologies showed positive ANCA, low C3 and C4, and high Bartonella titers. Repeat kidney biopsy revealed mesangioproliferative GN with full-house immune complex deposition in the mesangium and also in the subendothelial, subepithelial and intramembranous spaces. Bartonella DNA was detected, leading to hospital readmission for bacteremia and pulmonic valve vegetation. He was treated with antibiotics leading to and then following valve replacement. Discussion: The differential diagnosis for immune complex glomerulonephritis includes autoimmune disease, malignancy and infection which may often be missed at the time of acute infection due to mild symptoms and a negative infectious workup due to a fastidious and/or slow-growing microbe. Bartonella is most often diagnosed in the later stages of infection with elevated IgG titers rather than IgM and PCR as it is a facultative intracellular bacterium, rarely isolated in culture and only fleetingly found in the blood. When the kidney biopsy shows an immune complex glomerulonephritis, always consider smoldering infections, especially if the patient is immunocompromised or has a history of cardiac valve surgery.