Background Corynebacterium striatum i s a member of the non-diphtherial corynebacteria, which are ubiquitous in nature and generally colonize the skin and mucous membranes of humans. Rarely, it causes infective endocarditis (IE). We report a case of rare left atrial bacterial vegetative mass due to C. striatum masquerading as a myxoma identified through a tortuous diagnostic process, and present a brief review of the relevant literature. Case presentation We present a case of 63-year-old man who presented with progressively worsening dyspnea on exertion and lower leg edema, and was diagnosed with heart failure. Transesophageal echocardiography (TEE) revealed that the left atrium was filled with a 2.7?cm?×?2.6?cm mass. The patient, who had no signs of infection or related risk factors, was suspected of having a left atrial myxoma clinically. After excising the mass, the histopathology suggested thrombus with no myxocytes. Postoperatively, a fever appeared and C. striatum was isolated from the blood cultures. Although antibiotics were used, the symptoms of heart failure worsened gradually and echocardiography revealed valve vegetation. The patient underwent a second operation because of IE. Surprisingly, the mass was confirmed to be a bacterial vegetation due to C. striatum based on Gram staining at a 1000× magnification, although this was not noted on routine pathological examination of the two surgical specimens. Conclusions Physicians should be aware of Corynebacterium in blood cultures, which cannot simply be assumed to be a contaminant. A diagnosis of IE should be suspected, particularly in high-risk patients or those with an unexplained fever. Our patient had IE due to C. striatum with no risk factors. This case supports the diagnosis of IE using a combination of pathology and etiology.
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