Potential for FDG-PET/CT identifying causes of fever of unknown origin

2011 Objectives: (1) Review current guidelines for assessing an imaging modality’s efficacy in identifying the cause of fever of unknown origin (FUO) (2) Highlight the efficacy of 18F-fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) in assessing the cause of FUO. Methods: FUO is characterized as fever with a duration of more than three weeks with no evident cause after appropriate investigations. The most common causes of FUO are infections, malignancies, non-infectious inflammatory diseases, or other pathologies. Up to 50% of FUO cases are undiagnosed due to lack of an effective imaging modality. FDG-PET/CT is suitable for detecting the source of FUO because FDG uptake is increased in infections, cancers, and inflammation. Results: An abnormal FDG-PET/CT scan is associated with a greater likelihood of identifying the cause of FUO, while a negative scan has a low probability of resulting in a definitive diagnosis. Neutrophils and lymphocytes accumulate at the site of infection, and are detected with great sensitivity and specificity by an increase in FDG uptake. FDG-PET/CT scans can be used to guide biopsies, which are important in the diagnosis of vasculitis, tuberculosis, and other infections that are common causes of FUO. The high correlation between elevated C-reactive protein (CRP) levels and positive FDG-PET/CT scans demonstrates the usefulness of FDG uptake in FUO cases due to inflammation. The clinical helpfulness of FDG-PET/CT in diagnosing IBD, rheumatoid arthritis, Still’s disease, and other inflammatory diseases is well documented. FDG-PET/CT results in increased uptake SUV values in most malignancies, and should be one of the differential diagnoses when investigating FUO cases. Hodgkin’s disease, aggressive non-Hodgkin’s lymphoma, colorectal cancer, and pancreatic cancer are all malignancies that have been identified as causes of FUO with FDG-PET/CT. Traditionally, gallium-67 citrate scintigraphy was used to image FUO cases, but is suboptimal compared to FDG-PET/CT because of the high radiation dose, high inter- and intraoperator variability, and greater delay between injection and imaging. Radiolabeled autologous white blood cells (WBC) scintigraphy is not ideal either because not all causes of FUO involve greater WBC presence. Identifying the proportion of scans that were contributory versus those that had no influence on the final diagnosis of the cause of FUO will allow for better comparison of studies than using sensitivity, specificity, and predictive values. Conclusions: Using diagnostic usefulness as the key metric in assessing the effectiveness of an imaging modality in diagnosing the cause of FUO will further distinguish FDG-PET/CT as an invaluable tool in FUO cases. FDG-PET/CT scans can guide localizing biopsies and improve treatment triage, bolstering its clinical utility. The ability to anatomically correlate regions of high FDG uptake makes FDG-PET/CT a very promising modality for assessing FUO. @font-face \t{font-family:\"Cambria Math\"; \tpanose-1:2 4 5 3 5 4 6 3 2 4; \tmso-font-charset:0; \tmso-generic-font-family:roman; \tmso-font-pitch:variable; \tmso-font-signature:-536870145 1107305727 0 0 415 0;}p.MsoNormal, li.MsoNormal, div.MsoNormal \t{mso-style-unhide:no; \tmso-style-qformat:yes; \tmso-style-parent:\"\"; \tmargin:0in; \tline-height:115%; \tmso-pagination:widow-orphan; \tfont-size:11.0pt; \tfont-family:\"Arial\",sans-serif; \tmso-fareast-font-family:Arial; \tmso-ansi-language:EN;}.MsoChpDefault \t{mso-style-type:export-only; \tmso-default-props:yes; \tfont-size:11.0pt; \tmso-ansi-font-size:11.0pt; \tmso-bidi-font-size:11.0pt; \tfont-family:\"Arial\",sans-serif; \tmso-ascii-font-family:Arial; \tmso-fareast-font-family:Arial; \tmso-hansi-font-family:Arial; \tmso-bidi-font-family:Arial; \tmso-ansi-language:EN;}.MsoPapDefault \t{mso-style-type:export-only; \tline-height:115%;}div.WordSection1 \t{page:WordSection1;}