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FDG PET/CT Has 90% Overall Accuracy for Diagnosis of Fever of Unknown Origin

November 13, 2009
Written by: , Filed in: Emergency Radiology
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Background
Fever of Unknown Origin (FUO) remains a difficult clinical challenge, often with delayed initiation of appropriate treatment. Possible etiologies of FUO include infection, noninfectious inflammatory processes, and neoplasm; F-18 FDG, as an indicator of intracellular glucose metabolism, is increased in all three.

The objective of a recent study was to assess the role of PET/CT in the investigation of FUO.

FDG PET/CT has a high accuracy in the initial non-invasive diagnosis of fever of unknown origin (FUO).

Design
Prospective clinical trial.

Participants
Fifty-three consecutive patients admitted to the hospital for investigation of FUO were enrolled and underwent FDG PET/CT. Five patients died prior to receiving a final diagnosis, and were excluded from analysis, leaving 48 remaining patients.

Methodology
Studies were reviewed prospectively by a nuclear medicine physician and radiologist, who were aware of the patients’ clinical history and results of prior testing. Foci of increased FDG uptake, localized by hybrid imaging to an area that did not correspond to physiologic bio-distribution of radiotracer, were defined as positive. Findings were judged as true-positive (TP), false-positive (FP), or negative based on results of other studies and clinical follow-up.

Final diagnosis was determined by the treating physician and confirmed by one of the investigators, and was based on histopathology in nine patients, on microbiologic or serologic assays in 10 patients, on clinical diagnostic criteria defined by the treating physician in eight patients, and on clinical and imaging follow-up of at least 12 months in 21 patients.

Emergency Radiology The University of Washington School of Medicine, Harborview Medical Center, Department of Radiology * Features case-based presentations with extensive explanations – 15 hours of video * What, when, and how of imaging in relation to specific topics in emergency medicine * Stresses the interaction and communication required to be an effective part of the emergency medicine team * Provides guidance in diagnosis of polytrauma, commonly missed diagnoses, and when to change existing protocols Click here to read more or order: Emergency Radiology

Results
Scans demonstrated foci of increased FDG uptake in 27 studies. These were TP in 22 patients, including localized infection in 9, inflammation in 10, and malignancy in 3 patients.

There were 5 FP cases. These included 2 patients with inhomogeneous uptake throughout the skeleton, 2 additional patients had focal uptake in axillary lymph nodes, and a single patient had a paravertebral soft tissue mass.

FDG PET/CT showed no abnormalities in 21 patients, and no focal disease was diagnosed in any of these patients. Two patients had UTIs, 1 had typhoid, 1 had Q fever, 1 had cytomegalovirus infection, and 1 had drug-induced fever. In the other 15 patients, FUO resolved spontaneously with no further disease for one to three years.

Conclusions
FDG PET/CT for the diagnosis of focal disease processes had a sensitivity of 100%, specificity of 81%, PPV of 81%, and NPV of 100%, with an overall accuracy of 90%. PET/CT contributed to final diagnosis in 46% of the study population.

Reviewer’s Comments
I find these results very promising. As usual, the hurdle to extending FDG PET/CT to FUO will be in reimbursement. It appears from the data that use of this test effectively determines a diagnosis and shortens patient work-up, therefore it may make economic sense to perform this diagnostic study.

Author: Lionel S. Zuckier, MD

Reference:
Keidar Z, Gurman-Balbir A, et al. Fever of Unknown Origin: The Role of 18F-FDG PET/CT. J Nucl Med; 2008;49 (December): 1980-1985:

Emergency Radiology The University of Washington School of Medicine, Harborview Medical Center, Department of Radiology * Features case-based presentations with extensive explanations – 15 hours of video * What, when, and how of imaging in relation to specific topics in emergency medicine * Stresses the interaction and communication required to be an effective part of the emergency medicine team * Provides guidance in diagnosis of polytrauma, commonly missed diagnoses, and when to change existing protocols Click here to read more or order: Emergency Radiology
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