The yield of F18 FDG PET-CT for the investigation of fever of unknown origin, compared with diagnostic CT

Abstract

Background: 18F-Fluoro-2-deoxy-D-glucose (FDG) positron emission tomography, with contrast enhanced CT (PET-CT), is recommended as a first or a second-line imaging method for the evaluation of patients with fever of unknown origin (FUO). We evaluated the yield of PET-CT vs. contrast enhanced CT (alone) for the diagnosis of classical FUO.

Methods: A single center, 8-year retrospective cohort study. All hospitalized patients who underwent PET-CT for the investigation of classical FUO between 1/2012-1/2020 were included. The final diagnosis, based on clinical, microbiological, radiological and pathological data available at the latest follow-up, at least six months after discharge, was determined. For each case, we determined whether the diagnosis would have been reached based on the CT scan alone, or based on the PET-CT (thus, defining PET-CT as necessary). We compared the overall sensitivity and specificity results for both PET-CT and CT scan. Variables that were found to be significantly associated with PET-CT necessity on univariable analysis were entered into a multivariable logistic regression analysis. The results of the regression model were reported in odds ratios (OR) and 95% confidence intervals (CI).

Result: A total of 303 patients with classical FUO were referred for PET-CT. The final diagnoses included infectious diseases in 111/303 patients (36.5%), malignancies in 56/303 patients (18.4%) and non-infectious inflammatory conditions in 52/303 patients (17.1%). FUO resolved without diagnosis in 84/303 patients (28%). The overall sensitivity and specificity of the PET-CT scans were 88.7% and 80.9%, respectively, and for the CT scans were 75.2% and 90.2%, respectively. PET-CT had superior sensitivity vs CT (p=0.00) for all subgroups, with generally decreased specificity than CT for infections and inflammatory conditions. PET-CT was determined as necessary in 26% (79/303) of the patients. Endovascular infection, hematological malignancy and large vessel vasculitis were the only factors associated with PET-CT necessity on multivariable analysis.

Conclusions: PET-CT offers superior sensitivity with slightly decreased specificity for the diagnosis of classical FUO compared to diagnostic CT. We recommend PET-CT as the imaging modality of choice for patients with classical FUO, when endovascular infection, hematological malignancy or large vessel vasculitis are suspected.

Keywords: FUO; Fever of unknown origin; PET-CT; Sensitivity; Specificity.