Four consecutive 18F-FDG-PET/CT scans of the same patient with a prosthetic heart valve (PHV, Perimount 21 mm biological valve implanted 2 years prior) in the aortic position, with target-to-background ratios (TBR, SUVmax PHV divided by SUVmean aortic blood pool). Patient presented with fever, malaise, and diarrhoea after returning from a trip abroad. Fever persisted under initial antibiotic treatment with ceftriaxone and gentamycin, and FDG-PET/CT was performed (Panel A) which showed reactive bone marrow but only very little uptake around the PHV, and endocarditis was deemed unlikely. Blood cultures were positive for Pseudomonas aeruginosa, and antibiotic treatment was changed accordingly. Malaise and diarrhoea abated under this treatment, but fever persisted. Echocardiography showed no signs of endocarditis, but follow-up PET/CT after 2 weeks (Panel B) revealed focal and intense uptake near the former non-coronary cusp (NCC) of the aortic valve, adjacent to the PHV, without other infectious foci. Based on these findings, the clinical diagnosis of PHV endocarditis was made. Therefore, antibiotic treatment was intensified and prolonged to a total of 6 weeks. Follow-up PET/CT 2 days after end of antibiotics, with no clinical or haematological signs of infection, again showed minimal uptake around the PHV (Panel C). However, 3 weeks after cessation of antibiotics, the fever returned, blood cultures again showed P. aeruginosa, and pathological uptake near the valve returned (Panel D). The PHV was surgically removed and culture of a fragment of aortic wall near the NCC was positive for P. aeruginosa even though antibiotic treatment had been reinitiated before surgery. These images show the ability of FDG-PET/CT to follow disease activity in PHV endocarditis, but also that false-negative results for the presence of pathogens may be induced by scanning during or directly after antibiotic therapy if all signs and symptoms have abated. In such cases, it is probably wise to postpone follow-up until after cessation of therapy or signs of infection return.
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Scholtens et al. (2015) studied this question.