FDG-PET Imaging Can Identify Source of FUO

Nancy A. Melville

June 14, 2011

June 14, 2011 (San Antonio, Texas) — Diagnostic imaging using positron emission tomography (PET) in combination with the isotope fluorodeoxyglucose (FDG) can play a critical role in quickly revealing the causes of fevers of unknown origin (FUO), according to the results of a multicenter Japanese trial presented here at the Society of Nuclear Medicine 2011 Annual Meeting.

FUOs can persist for 2 to 3 weeks, or longer, despite days of in-hospital evaluation and testing. Prolonged efforts to diagnose the fever can be frustrating, time-consuming, and costly, said lead author Kozuo Kubota, MD, PhD, chief of nuclear medicine at the National Center for Global Health and Medicine in Tokyo, Japan.

"When there is a fever of unknown origin, clinicians often have to perform a number of tests, including blood chemistry examinations and bacteriological examinations of sputum or urine," he said.

"Statistics show that even after these extensive investigations, about half of patients remain undiagnosed regarding the cause of the fever."

Clinicians can try imaging patients with FUO using computed tomography or gallium scans, but Dr. Kubota said FDG appears to be a more effective tool than gallium scanning for a number of reasons.

"Gallium scans have been reported to have a much lower value, with a sensitivity of 67% at best, or sometimes far lower — at the 20% to 30% level — largely because of the difference in resolution," he explained.

The time required to obtain gallium scan results is another drawback, Dr. Kubota noted. "FDG PET provides the results only 90 minutes after the start of examination, whereas with gallium imaging, we have to wait 3 to 4 days."

In an effort to investigate the value of FDG PET in diagnosing FUO, Dr. Kubota and his team evaluated 81 patients with FUO at 6 institutions between July 2006 and December 2007.

The measures included the efficacy of the FDG PET in analyzing the FUO, FDG uptake by visual evaluation, the clinical impact on therapeutic decisions rated on a 4-grade scale, and additional information obtained with FDG PET.

The results revealed diagnoses in 4 categories: infection; arthritis, vasculitis, autoimmune, collagen disease (A/V); tumor/granuloma; and other/unknown.

The highest sensitivity — 100% — was observed in tumor/granuloma detection (7 of 7); followed by infection, with a sensitivity of 89% (24 of 27); A/V, with a sensitivity of 65% (11 of 17); and other/unknown, with a sensitivity of 0% (0 of 1).

The same tendency was seen with clinical impact and mean FDG score. The other/unknown group showed a high specificity (84%; 16 of 19) and accurately ruled out active focal inflammatory diseases and malignancy.

In an example of the imaging tool's effectiveness, the researchers described the case of a 50-year-old man with kidney failure and FUO.

Imaging with FDG PET revealed increased isotope uptake and fibrosis around an aortic graft. A blood culture subsequently confirmed a graft infection involving Staphylococcus aureus, and a quick diagnosis was made.

"FDG PET imaging is very sensitive, both for cancer and for focal inflammation, and is easy for whole-body imaging, allowing for the detection of a true active lesion," Dr. Kubota explained.

"The imaging will shorten the long list of futile multiple examinations needed for patients in reaching the final diagnosis," Dr. Kubota said. "It will help patients to have the most effective therapy quickly, it may improve the prognosis, and it may save on cost."

The study's findings underscore how important FDG PET imaging can be in unraveling such tough-to-diagnose cases, said Michael M. Graham, MD, PhD, professor of radiology and radiation oncology and director of nuclear medicine at the University of Iowa College of Medicine in Iowa City.

"This is a problem that has existed in medicine for a long time. The patients present with fever and they are clearly ill," said Dr. Graham. "Even with modern medicine, we may be unable to come up with the answer after weeks of effort," he said. "Yet in about an hour to an hour and a half with FDG PET, we can come up with an answer with excellent sensitivity."

"It may not be accurate every single time, but if it wasn't done, the cause would remain a mystery and you'd likely just have to treat the patient with antibiotics and hope for the best," Dr. Graham added.

"I regard this as a huge step forward and I think it's going to change the way we approach this particular problem," he noted.

Dr. Kubota and Dr. Graham have disclosed no relevant financial relationships.

Society of Nuclear Medicine (SNM) 2011 Annual Meeting: Abstract 16. Presented June 5, 2011.