18F-FDG PET in detecting metastatic infectious disease

Timely identification of metastatic complications of bloodstream infections due to spreading of the microorganisms to distant sites, although critical, is often difficult. As 18F-FDG accumulates in activated leukocytes in infectious lesions, 18F-FDG PET represents a promising imaging technique in these patients. The aim of this study was to assess the value of 18F-FDG PET in detecting infectious foci in patients at high risk of metastatic complications.

The results of all 18F-FDG PET scans ordered because of suspected metastatic infection from October 1998 to September 2004 were analyzed retrospectively. These results were compared with conventional investigation techniques and the final clinical diagnosis.

The results of 40 18F-FDG PET scans were evaluated. In 60% of all episodes, Gram-positive bacteria were cultured, in 18% Gram-negative bacteria, in 20% Candida spp., and in 3% the infection was polymicrobial. Metastatic complications were diagnosed in 75% of all episodes. A median number of 4 diagnostic procedures to search for metastatic infection had been performed before 18F-FDG PET was ordered. 18F-FDG PET diagnosed a clinically relevant new focus in 45% of cases and confirmed abnormalities already diagnosed in 30% of cases. The positive predictive value of 18F-FDG PET was 91% and the negative predictive value was 100%.

18F-FDG PET is a valuable imaging technique in patients at high risk of metastatic infectious disease, even when the results of other diagnostic procedures are normal.