A Case of Nontuberculous Mycobacterial Prosthetic Valve Endocarditis

Prosthetic valve endocarditis (PVE) caused by rapidly growing nontuberculous mycobacteria (NTM) is rare and diagnostically challenging. Cases involving organisms within the Mycobacterium smegmatis group are exceptionally uncommon.

We report the case of an 82-year-old man who developed recurrent fevers and persistent Mycobacterium smegmatis bacteremia after bioprosthetic aortic valve replacement and left atrial appendage occlusion. Serial transesophageal echocardiograms remained nondiagnostic despite ongoing symptoms and bacteremia. Subsequent fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) demonstrated intense uptake surrounding the prosthetic aortic valve and the left atrial appendage occlusion device, with maximum standardized uptake values (SUVs) of 9.2 and 5.8, respectively. Repeat surgery revealed a circumferential aortic root abscess, and the valve isolate was reported as Mycobacterium goodii by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Because both reported identifications fall within the Mycobacterium smegmatis group, the infection was classified at the group level; the species-level assignment remained unresolved. Postoperatively, routine and acid-fast bacillus blood cultures were negative, and the patient's fevers resolved after surgical source control and antimicrobial therapy. After discharge, the patient completed approximately five months of a clofazimine-containing multidrug antimicrobial regimen. At three years of clinical follow-up, he remained alive, asymptomatic, and free of recurrent infection.

This case highlights the difficulty of diagnosing NTM prosthetic valve endocarditis when echocardiography is unrevealing and illustrates how PET/CT contributes important diagnostic information in suspected prosthetic cardiac infection. It also adds to the limited literature on Mycobacterium smegmatis group endocarditis and demonstrates the successful incorporation of clofazimine within a multidisciplinary treatment strategy.