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J Nucl Med. 2008 Dec;49(12):1980-5. doi: 10.2967/jnumed.108.054692. Epub 2008 Nov 7.

Fever of unknown origin: the role of 18F-FDG PET/CT.

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  • 1Department of Nuclear Medicine, Rambam Health Care Campus, Haifa, Israel.


Fever of unknown origin (FUO) is a challenging diagnostic problem. Timely identification and precise localization of the causing process are critical for appropriate patient management. The present prospective study evaluates the role of PET/CT using (18)F-FDG in the investigation of FUO.


A total of 48 consecutive patients (25 men, 23 women; age range, 24-82 y) with FUO underwent (18)F-FDG PET/CT scans. FUO was defined as a fever of more than 38.3 degrees C that lasted for more than 3 wk and failure to reach diagnosis after more than 1 wk of inpatient investigation. The performance of PET/CT for identifying the etiology of FUO was assessed. Final diagnosis was based on histopathology, microbiologic assays, or clinical and imaging follow-up.


PET/CT detected suggestive foci of increased (18)F-FDG uptake in 27 patients. In 22 of these 27 positive studies (81%), PET/CT identified the underlying disease and diagnosed infection in 9 patients, an inflammatory process in 10 patients, and malignancy in 3 patients. (18)F-FDG PET/CT was negative in 21 patients. All these patients were diagnosed as having systemic nonfocal infection or drug-induced fever or showed spontaneous resolution of the febrile state with no further evidence of a localized inflammatory, infectious, or malignant process for a clinical follow-up period of 12-36 mo.


(18)F-FDG PET/CT identified the underlying cause of the fever in 46% of the present study population and contributed to the diagnosis or exclusion of a focal pathologic etiology of the febrile state in 90% of patients. (18)F-FDG PET/CT has a high negative predictive value (100%) for assessment of FUO. If confirmed by further studies, (18)F-FDG PET/CT may be used in the future as an initial noninvasive diagnostic modality for assessment of this group of patients.

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