TORONTO — Positron emission tomography using
Dr. Oyen, professor of nuclear medicine at Radboud University Nijmegen (Netherlands) Medical Centre, and colleagues assessed the value of FDG-PET in helping detect infectious lesions that may have spread to other sites in patients with bacteremia or fungemia—what they term “secondary metastatic infection.” Prior to undergoing FDG-PET, each patient had undergone a mean of four conventional diagnostic procedures, including blood work, ultrasound studies, and CT scans.
The retrospective review included 40 FDG-PET scans performed at the center between October 1998 and September 2004. A total of 41 FDG-PET scans were performed in 39 patients, but 1 scan was excluded because the patient's claustrophobia led to an incomplete scan. The scans were ordered by referring physicians because patients had persistent fever despite an adequate course of antibiotics, and therefore were suspected of harboring a secondary metastatic infection. Blood cultures confirmed that about 60% of the episodes resulted from gram-positive bacteria, whereas about 18% resulted from gram-negative bacteria and about 20% resulted from Candida species. The source of infection was polymicrobial in the remaining episodes.
Of the group, “30% had abnormalities on previous diagnostic techniques, but physicians were not satisfied with the conventional diagnoses, and these abnormalities were confirmed by FDG-PET,” Dr. Oyen said in an interview.
Overall, 45% of the 40 scans provided clinically relevant, new information. FDG-PET confirmed already diagnosed abnormalities in another 30% of the scans, yielding a positive predictive value of 91%. No patient developed infectious complications when the FDG-PET was negative, yielding a negative predictive value of 100% in this small series of patients.
The high diagnostic accuracy of FDG-PET in this series may not apply to lower-risk patients whose bacteremia or fungemia is less likely to have spread. Nevertheless, FDG-PET appears to be a “valuable imaging technique” for high-risk patients, he noted.
The researchers are planning a prospective study to test whether FDG-PET is useful in lower-risk patients with bacterial or fungal infections in the blood.