Lessons learned from splenic infarcts with fever of unknown origin (FUO): culture-negative endocarditis (CNE) or malignancy?

Culture negative endocarditis (CNE) is a common concern in patients with fever, heart murmur, cardiac vegetation, and negative blood cultures. The diagnosis of CNE is not based only on negative blood cultures and a cardiac vegetation. The clinical definition of CNE is based on negative blood cultures plus the findings of culture positive infective endocarditis (IE), e.g., fever, cardiac vegetation, splenomegaly, peripheral manifestations. Because embolic splenic infarcts may occur with culture positive IE, some may assume that splenic infarcts are a sign of CNE. Previously, CNE was due to fastidious and non-culturable organisms. With current diagnostic methods, fastidious organisms grow in 2–3 days. Therefore, fastidious IE are a subset of culture positive IE, but do not represent true CNE. We describe a case of an elderly female who presented with a fever of unknown origin (FUO) and multiple splenic infarcts thought by some to represent CNE. An extensive workup for CNE pathogens was negative. The final cause of her splenic infarcts was a diffuse large B-cell lymphoma (DLBCL). Review of the literature, as well as this case, confirms that splenic infarcts are not a feature of CNE. In patients with fever, splenic infarcts, and negative blood cultures, physicians should search for an alternate explanation rather than CNE, e.g., malignancy and hypercoaguable state (lupus anticoagulant).