Case Presentation: This is a 52 year old Hispanic male with a history of bioprosthetic aortic valve replacement four years prior who presented with chest pain and abdominal pain. The patient was recently treated for aortic valve endocarditis with long-term intravenous antibiotic therapy lasting six weeks. The patient admitted to a one month history of fever, chills, and left upper quadrant discomfort. Upon presentation, he was febrile with laboratory values that were significant for leukocytosis and mild troponinemia. The patient was admitted with a working diagnosis of sepsis of unknown etiology. Blood cultures were drawn, and the patient was started on broad spectrum antibiotics. Echocardiogram was suggestive of a vegetation involving the bioprosthetic aortic valve. A computed tomography of the chest revealed signs of a pseudoaneurysm involving the ascending aorta (Figure 1 and 2). Blood cultures eventually grew coagulase-negative staphylococci. Patient was ultimately cleared for surgery and underwent pseudoaneurysm repair with aortic bioprosthetic valve replacement.

Discussion: It is well known that Staphylococcus lugdunensis not only causes skin and soft tissue infections, but has also been implicated in cases of infective endocarditis. It is unusual for this organism to be considered a contaminant when isolated on blood cultures (1). S.Lugdunensis is well known for its propensity towards an aggressive clinical course, and is said to behave similarly to S.aureus. Although this rare microbe has a predilection to affect native valves more often, prosthetic valve involvement has been linked with a more sinister outcome, with higher rates of complications such as heart failure, periannular abscess, embolization, shock and death (2). Mortality rates are found to be around 38.8- 70%, with higher rates being found in prosthetic valve involvement as compared to native valves (3). The formation of mycotic aneurysms (pseudoaneurysms) secondary to S.Lugdunensis is found to be an extremely rare occurrence with most of the data being available only through case reports. Pseudoaneurysms in these cases were found to involve the intracranial vessels, left ventricle, aorta, superior mesenteric and tibial arteries. The mechanism underpinning the aggressive nature S. lugdunensis is largely unknown. However, it is postulated that certain adherence proteins such as the vWF and Fibrinogen-binding proteins may aid in the adherence of the bacterium to tissue and artificial surfaces (4). The dislodgement of septic emboli may also cause seeding of the bacteria in distant.

Conclusions: It is important to recognize S.lugdunensis endocarditis as early as possible in view of its high mortality. This case was unique as it not only involved a prosthetic valve, but also revealed the presence of a pseudo-aneurysm, which is extremely rare. It is vital to keep Staphylococcus lugdunensis in mind as a differential organism for bacterial endocarditis, especially in the presence of a pseudoaneurysm. Doing so will help to better manage these patients as well as improve outcomes.