18F-FDG-PET/CT in unexplained elevated inflammatory markers. Joining entities

The Diagnostic Yield of [18F]FDG-PET/CT in a Heterogeneous In-Patient Population with Suspected Infection or Inflammation Is Comparable to Findings in Patients with Classic Fever of Unknown Origin

INTRODUCTION

Suspected infection or inflammation of unknown origin in in-patients remains challenging. Literature on [18F]FDG-PET/CT is abundant in classic fever of unknown origin (FUO), but evidence is complex and may not always reflect clinical reality. This study explores the application of [18F]FDG-PET/CT in a diverse clinical population of in-patients with suspected infection not defined by stringent FUO-criteria.

METHODS

Retrospective chart review of consecutive in-patients who underwent [18F]FDG-PET/CT in the workup of suspected infection or inflammation from 1 July 2022 to 31 December 2022 was conducted. We evaluated indications, diagnostic yield, and clinical impact of [18F]FDG-PET/CT, and compared the findings of [18F]FDG-PET/CT and stand-alone CT. Univariate logistic regression assessed associations between [18F]FDG-PET/CT outcome and clinical parameters. Receiver operating characteristic curve (ROC) analysis evaluated diagnostic performance.

RESULTS

77 patients met the inclusion criteria. [18F]FDG-PET/CT established a diagnosis in 35% of cases, ruled out focal infection in 26%, and thus was helpful in 61% of patients. It prompted 72 additional examinations resulting in seven incidental diagnoses, including two cancers. Antibiotic treatment was changed in 26% of cases. Regression analysis found white blood cell counts (WBC) associated with true positive outcomes. [18F]FDG-PET/CT was compared to stand-alone CT findings, and was concordant in 69% of cases.

CONCLUSIONS

Results were comparable to findings in more classic FUO. [18F]FDG-PET/CT was clinically helpful in 61% of cases but also prompted many additional examinations with relatively few clinically important findings. WBC count was a predictor of true positive outcome. CT and [18F]FDG-PET/CT were discordant in 31%, of cases, especially in cases of endocarditis and spondylodiscitis.

The Contribution of 18F FDG PET-CT for the Investigation of Fever of Unknown Origin and Inflammation of Unknown Origin

BACKGROUND

Fever of unknown origin and inflammation of unknown origin are highly challenging diagnostic conditions. The current practice for evaluating patients is to conduct a positron emission tomography-computed tomography (PET-CT) scan as either a first- or a second-line modality. We aimed to assess the contributory effect of PET-CT to the diagnosis and compare it with the contributory effect of CT alone.

METHODS

We performed a systematic review and meta-analysis. We included all cohorts that examined the contribution of PET-CT to the investigation of classical fever of unknown origin and inflammation of unknown origin. The primary outcome was the contribution of PET-CT to the final diagnosis. Secondary outcomes were sensitivity and specificity of PET-CT and CT scans, and contribution of a CT scan. We pooled the results of all studies and calculated the pooled contributory effect of PET-CT.

RESULT

Thirty-six studies (3516 patients) were included in the systematic review. The pooled contribution of PET-CT was 75.4%. The compiled sensitivity and specificity values for all studies were 85.9% and 59.5%, respectively. Five studies (405 patients) compared between the PET-CT component and the total body CT component. The pooled contribution of a CT scan was 68%. The summed sensitivity and specificity values of a CT scan for all studies were 63.1% and 84.4%, respectively.

CONCLUSIONS

PET-CT has a contributory effect of 75% for the diagnosis of fever of unknown origin and inflammation of unknown origin. PET-CT had superior sensitivity and inferior specificity vs the CT scan.

Diagnostic value of FDG-PET/CT in the diagnostic work-up of inflammation of unknown origin

Introduction The present study aims to evaluate the clinical diagnostic value of FDG-PET/CT in patients with inflammation of unknown origin. Material and methods We retrospectively analyzed data of 130 patients who presented general inflammatory symptoms and/or elevated level of CRP and underwent FDG-PET/CT for the purpose of identifying unknown foci of inflammation. The accuracy of PET/CT findings was assessed against the standard of eventual clinical diagnosis e.g. results of pathology, microbiology or other imaging methods. Results In 99/130 patients (76 %) a final diagnosis was established, FDG-PET/CT showed a sensitivity and specificity of each 93 %. A decreased pseudocholinesterase is associated with a higher SUVmax value and with a higher CRP value whereas no significant relationship was found between elevated CRP values and the SUVmax, although higher CRP values are associated significantly with a true positive PET/CT result. Conclusion FDG-PET/CT is a highly sensitive, specific and accurate method for the detection of foci of inflammation of unknown origin. The combination of decreased pseudocholinesterase and increased CRP levels may be a useful tool to select patients for FDG PET/CT.

Molecular Imaging of Fever of Unknown Origin: An Update

¹⁸F-FDG PET/CT, ⁶⁷Ga-citrate and white blood cell (WBC) scintigraphy are molecular imaging techniques currently used in the diagnostic workup of fever of unknown origin. However, it is unknown which technique fits which patient group best. A systematic literature search has been performed for original articles regarding the use of molecular imaging in fever of unknown origin. A total of 820 eligible studies were screened of which 63 articles evaluating 5094 patients met the inclusion criteria. ¹⁸F-FDG PET/CT provided good diagnostic accuracy (with a weighted mean sensitivity, specificity, positive predicting value, negative predictive value, accuracy and helpfulness of 84.4%, 61.8%, 80.7%, 67.8%, 76.3%, and 61.1%, respectively). Even within specific patient groups such as children, elderly, patients with connective tissue diseases, patients on renal replacement therapy, and HIV-infected patients, ¹⁸F-FDG PET/CT provided good diagnostic values. For ⁶⁷Ga-citrate scintigraphy, the weighted mean sensitivity, specificity, positive predictive value, negative predictive value, and helpfulness were 42.2%, 80.3%, 82.4%, 41.9%, and 42.2%, respectively. WBC scintigraphy shows a weighted mean sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 73.5%, 86.3%, 79.1%, 82.4%, and 79.5%, respectively. However, compared to ⁶⁷Ga-citrate and WBC scintigraphy, significantly more research has been performed using ¹⁸F-FDG PET/CT and ¹⁸F-FDG PET/CT has the advantage of relatively short procedural duration; it is therefore the preferred molecular diagnostic imaging technique. ⁶⁷Ga-citrate and WBC scintigraphy can only be considered if ¹⁸F-FDG PET/CT is not available.

Emerging Trends in Radionuclide Imaging of Infection and Inflammation in Pediatrics: Focus on FDG PET/CT and Immune Reactivity

The most common indication for ¹⁸F-FDG PET/CT is tumor imaging, which may be performed for initial diagnosis, staging, therapeutic response monitoring, surveillance, or suspected recurrence. In the routine practice of pediatric nuclear medicine, most infectious, inflammatory, and autoimmune processes that are detected on ¹⁸F-FDG PET/CT imaging - except for imaging in fever or inflammation of unknown origin - are coincidental and not the main indication for image acquisition. However, interpreting these "coincidental" findings is of utmost importance to avoid erroneously attributing these findings to a neoplastic process. We review the recent literature on fever of unknown origin as well as inflammation of unknown origin in pediatrics and then focus on the ¹⁸F FDG PET/CT imaging findings seen in two specific entities with increased immune reactivity: hemophagocytic lymphohistiocytosis syndrome and the immune-related adverse events associated with checkpoint inhibitors. We will subsequently close with two sections highlighting related topics and relevant references for further reading.

FDG-PET/CT in Fever of Unknown Origin, Bacteremia, and Febrile Neutropenia

Fever of unknown origin, bacteremia, and febrile neutropenia are diagnostic challenges. FDG-PET/CT is a well-established modality in infection imaging and the literature increasingly supports its use in these settings. In fever of unknown origin, FDG-PET/CT is helpful, but diagnostic yield depends on patient selection and inflammatory markers. In bacteremia, FDG-PET/CT is cost-effective, reduces morbidity and mortality, and impacts treatment strategy. Although use of FDG-PET/CT in these domains is not established as part of a definitive diagnostic strategy, FDG-PET/CT may help establish final diagnosis in a difficult population and should be considered early in the diagnostic process.