Introduction
Fever of unknown origin (FUO) is a frequently encountered condition on internal medicine wards. It was first defined in 1961 as a fever greater than 38.3°C (101°F) for 3 weeks or more, whose origin is not identified despite a thorough work-up [1]. The recommended work-up has been modified over the years. While an abundance of studies may aid in the diagnosis, FUO often poses a great challenge to clinicians, and nearly half the patients ultimately do not receive a definitive diagnosis [2-4].
Positron emission tomography with computed tomography (PET/CT) combines regular CT with nuclear imaging based on the enhanced uptake of fluorodeoxyglucose (18F-FDG) by highly metabolic inflammatory and malignant cells. In the last decade, the PET/CT modality has gained widespread popularity. Several prospective and retrospective studies have suggested an important role of PET/CT in the work-up of FUO [5-8]. Nonetheless, much heterogeneity remains regarding the place of PET/CT within the algorithm of recommended studies. Some consider PET/CT a mandatory part of the work-up, while others regard it as a complementary test that may be performed following the use of other imaging modalities such as CT scans. Differences in study methodologies have produced variable results regarding the value of PET.
Given the lack of widespread availability of PET/CT, and its high costs, the population of FUO patients that is expected to gain benefit from this modality needs to be further characterized. In the current study, we assessed the utility of PET/CT in revealing the correct cause of FUO and evaluated for parameters that may increase the likelihood of diagnostic yield in patients with FUO.