Conference Coverage

Consider PET/CT when infectious source is a puzzler


 

REPORTING FROM RSNA 2019

– Dual positron emission tomography-computed tomography (PET/CT) scans changed the treatment course of nearly half of patients whose scans were positive for infection. In a single-center systematic review of 18fluorodeoxyglucose (FDG)–PET/CT scans, 55 of the 138 scans (40%) changed clinical management.

Dr. Benjamin Viglianti, nuclear medicine department, University of Michigan, Ann Arbor Kari Oakes/MDedge News

Dr. Benjamin Viglianti

Presenting the findings at the annual meeting of the Radiological Society of North America, Benjamin Viglianti, MD, PhD, said that PET/CT had particular utility in cases of bacteremia and endocarditis, in which the scans changed treatment in 46% of those cases.

Dr. Viglianti, a radiologist at the University of Michigan, Ann Arbor, explained that medical student and first author Anitha Menon, himself, and their collaborators deliberately used a broad definition of clinical management change. The management course was considered to change not only if an unknown infection site was discovered or if a new intervention was initiated after the scan, but also if antibiotic choice or duration was changed or an additional specialty was consulted.

Scans were included in the study if an infectious etiology was found in the scan and if the patient received an infectious disease consult. Bacteremia and endocarditis were the most frequent indications for scans and also the indications for which management was most frequently changed. When a vascular cause was the indication for the scan, management changed 41% of the time. For fevers of unknown origin, the scan changed management in 30% of the cases, while for osteomyelitis, management was changed for 28% of patients.

The investigators identified several broad themes from their review that pointed toward when clinicians might consider FDG-PET/CT imaging in infectious disease management.

The first, said Dr. Viglianti, was that “for patients with suspected vascular graft infection, PET/CT using FDG may be a good first-choice imaging modality.” He pointed to an illustrative case of a patient who was 1 month out from open repair of a thoracoabdominal aortic aneurysm. The patient had abdominal pain, epigastric tenderness and nausea, as well as an erythematous incision site. A CT scan just revealed an abdominal fluid collection, but the PET/CT scan showed radiotracer uptake at the prior repair site, indicating infection.

For patients with bacteremia, the investigators judged that FDG-PET/CT might be particularly useful in patients who have a graft, prosthetic valve, or cardiac device. Here, Dr. Viglianti and his collaborators highlighted the scan of a woman with DiGeorge syndrome who had received aortic root replacement for truncus arteriosis. She had been found to have persistent enterococcal bacteremia at high levels, but had been symptom free. To take a close look at the suspected infectious nidus, a transesophageal echocardiogram had been obtained, but this study didn’t turn up any clear masses or vegetations. The PET/CT scan, though, revealed avid FDG uptake in the area of the prosthesis.

Management course was not likely to be changed for patients with fever of unknown origin, but the investigators did note that whole-body PET/CT was useful to distinguish infectious etiologies from hematologic and oncologic processes. Their review included a patient who had Crohn’s disease and fever, myalgias, and upper abdominal pain, as well as liver enzyme elevation. The PET/CT showed radiotracer uptake within the spleen, which was enlarged. The scan also showed bone marrow uptake; these findings pointed toward hemophagocytic lymphohistiocytosis rather than an infectious etiology.

For osteomyelitis, said Dr. Viglianti, FDG-PET may have limited utility; it might be most useful when MRI is contraindicated. Within the study population, the investigators identified a patient who had chills and fever along with focal tenderness over the lumbar spine in the context of recent pyelonephritis of a graft kidney. Here, MRI findings were suspicious for osteomyelitis and diskitis, and the FDG uptake at the L4-L5 vertebral levels confirmed the MRI results.

When a patient with a prosthetic valve is suspected of having endocarditis, “cardiac PET/CT may be of high diagnostic value,” said Dr. Viglianti. For patients with endocarditis of native valves, though, a full-body FDG-PET/CT scan may spot septic emboli. A patient identified in the investigators’ review had been admitted for methicillin-resistant Staphylococcus aureus endocarditis. The patient, who had a history of intravenous drug use, received a transesophageal echocardiogram that found severe tricuspid valve regurgitation and vegetations. The whole-body PET/CT scan, though, revealed avid uptake in both buttocks, as well as thigh, ankle and calf muscles – a pattern “suspicious for infectious myositis,” said the researchers.

In discussion during the poster session, Dr. Viglianti said that, although reimbursement for PET/CT scans for infectious etiologies might not be feasible, it can still be a reasonable and even cost-effective choice. At his institution, he said, the requisite radioisotope is made in-house, twice daily, so it’s relatively easy to arrange scans. Since PET/CT scans can be acquired relatively quickly and there’s no delay while waiting for radiotracer uptake, clinical decisions can be made more quickly than when waiting for bone uptake for a technetium-99 scan, he said. This can have the effect of saving a night of hospitalization in many cases.

Dr. Viglianti and Ms. Menon reported that they had no relevant conflicts of interest. No outside sources of funding were reported.

SOURCE: Menon A et al. RSNA 2019, Abstract NM203-SDSUB1.

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