Diagnostic performance of 18 F-FDG-PET/CT in inflammation of unknown origin: A clinical series of 317 patients

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.

EANM consensus document on the use of [18F]FDG PET/CT in fever and inflammation of unknown origin

PURPOSE

Patients with fever and inflammation of unknown origin (FUO/IUO) are clinically challenging due to variable clinical presentations with nonspecific symptoms and many differential diagnoses. Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is increasingly used in FUO and IUO, but the optimal diagnostic strategy remains controversial. This consensus document aims to assist clinicians and nuclear medicine specialists in the appropriate use of [18F]FDG-PET/CT in FUO and IUO based on current evidence.

METHODS

A working group created by the EANM infection and inflammation committee performed a systematic literature search based on PICOs with "patients with FUO/IUO" as population, "[18F]FDG-PET/CT" as intervention, and several outcomes including pre-scan characteristics, scan protocol, diagnostic yield, impact on management, prognosis, and cost-effectiveness.

RESULTS

We included 68 articles published from 2001 to 2023: 9 systematic reviews, 49 original papers on general adult populations, and 10 original papers on specific populations. All papers were analysed and included in the evidence-based recommendations.

CONCLUSION

FUO and IUO remains a clinical challenge and [18F]FDG PET/CT has a definite role in the diagnostic pathway with an overall diagnostic yield or helpfulness in 50-60% of patients. A positive scan is often contributory by directly guiding treatment or subsequent diagnostic procedure. However, a negative scan may be equally important by excluding focal disease and predicting a favorable prognosis. Similar results are obtained in specific populations such as ICU-patients, children and HIV-patients.

Comparison of diagnostic spectrum between inflammation of unknown origin and fever of unknown origin: A systematic review and meta-analysis

BACKGROUND

Patients with inflammation of unknown origin (IUO) and fever of unknown origin (FUO) are commonly considered a single population. Differences in underlying causes between both groups may steer the diagnostic work-up.

METHODS

PubMed, Embase, Web of Science, and ClinicalTrials.gov were searched from July 2009 through December 2023. Studies including both FUO and IUO patients with a sample size of ≥20 were considered. The primary outcome was the difference in the rate of patients affected by predefined diagnostic categories according to meeting FUO or IUO criteria. Data were pooled using random-effects models.

RESULTS

A total of 8 studies met criteria for inclusion, with a total of 1452 patients (466 with IUO and 986 with FUO). The median rate of IUO patients among the included studies was 32 % (range 25-39 %). Patients with IUO had a lower likelihood of infection (OR 0.59 [95 % CI; 0.36-0.95]; I2 0 %). There were no significant differences in the rate of noninfectious inflammatory disorders, malignancies, miscellaneous disorders, or remaining undiagnosed. Comparison of diagnostic subgroups revealed that IUO patients were less likely to have systemic autoinflammatory disorders (OR 0.17 [95 % CI, 0.05-0.58]; I2 42 %) and more likely to have vasculitis (OR 2.04 [95 % CI, 1.23-3.38]; I2 21 %) and rheumatoid arthritis or spondylarthritis (OR 3.52 [95 % CI, 1.16-10.69]; I2 0 %).

CONCLUSION

Based on our findings, there is little reason to assume that FUO and IUO patients would benefit from a different initial diagnostic approach.

[18F]FDG-PET/CT in Polymyalgia Rheumatica: An Update and Future Aspects

Polymyalgia rheumatica (PMR) is an inflammatory disorder usually diagnosed in patients older than 50 years of age. It is characterized by sudden onset pain and prolonged morning stiffness in the scapular and/or pelvic girdle, sometimes debilitating and accompanied by constitutional symptoms such as weight loss. In approximately 20% of the cases, it is linked to giant cell arteritis (GCAV) representing a disease continuum. The diagnosis is mainly clinical and noninvasive imaging such as ultrasound of joints may be helpful. In atypical PMR cases, whole body imaging using [18F]FDG-PET/CT may be useful. First, to confirm or rule out the diagnosis of PMR, secondly, to assess the coexistence of a GCA, and thirdly to establish the differential diagnosis with other types of arthritides encountered in this age group, such as elderly-onset rheumatoid arthritis, spondyloarthropathies, crystal-induced arthropathies or the rare remittent seronegative symmetrical synovitis with pitting edema. Relatively typical patterns of [18F]FDG-PET/CT are well known, based on the clinical distribution of the disease (eg, scapular and pelvic girdle, interspinous bursae, sterno-costoclavicular joints, entheses), especially the hypermetabolism at the interspinous lumbar bursae that has shown the best post-test likelihood ratio in a meta-analysis. This article focuses on the differential diagnosis and on the visual and semi-quantitative tools that can be used to guide to the correct diagnosis of PMR as an add-on to the clinical picture. Further, we briefly discuss the options that can improve molecular imaging in the future for inflammatory rheumatisms in elderly.

PET/CT in Inflammatory and Auto-immune Disorders: Focus on Several Key Molecular Concepts, FDG, and Radiolabeled Probe Perspectives

Chronic immune diseases mainly include autoimmune and inflammatory diseases. Managing chronic inflammatory and autoimmune diseases has become a significant public health concern, and therapeutic advancements over the past 50 years have been substantial. As therapeutic tools continue to multiply, the challenge now lies in providing each patient with personalized care tailored to the specifics of their condition, ushering in the era of personalized medicine. Precise and holistic imaging is essential in this context to comprehensively map the inflammatory processes in each patient, identify prognostic factors, and monitor treatment responses and complications. Imaging of patients with inflammatory and autoimmune diseases must provide a comprehensive view of the body, enabling the whole-body mapping of systemic involvement. It should identify key cellular players in the pathology, involving both innate immunity (dendritic cells, macrophages), adaptive immunity (lymphocytes), and microenvironmental cells (stromal cells, tissue cells). As a highly sensitive imaging tool with vectorized molecular probe capabilities, PET/CT can be of high relevance in the management of numerous inflammatory and autoimmune diseases. Relying on key molecular concepts of immunity, the clinical usefulness of FDG-PET/CT in several relevant inflammatory and immune-inflammatory conditions, validated or emerging, will be discussed in this review, together with radiolabeled probe perspectives.

[Inflammatory syndrome of unknown origin and PET/CT: Economic and iatrogenic impacts of false positive]

INTRODUCTION

PET/CT is regularly used to investigate inflammatory syndrome of unknown origin (IUO), but hypermetabolisms found are not always consistent with the final diagnosis. The objective of the study was to assess the cost attributed to the diagnostic work-up for these false positives.

MATERIALS AND METHODS

We conducted an ancillary study on a previous retrospective cohort from the internal medicine department at Amiens university hospital in patients who had a PET/CT scan between October 2004 and April 2017. Patients were included if PET/CT had been prescribed to investigate IUO. Among the 763 PET/CT performed, 144 met the inclusion criteria and a false-positive rate of 17.4% (n=25) was reported.

RESULTS

Among these 25 patients, 21 underwent further investigations. The most frequently found hypermetabolic territories were digestive (n=12, mean SUVmax 8 [±4.33]) and osteoarticular (n=11, mean SUVmax 4.33 [±1.15]). The total cost of the 13 prescribed consultations was €390, the total cost of the 40 additional tests was €4,476 (mainly digestive endoscopies and radiological tests) and the total cost of medical transport was €572. The total cost of the 35 days of hospitalization specifically required to investigate these false positives was €22,952. In 23.8% (n=5), these investigations led to the incidental discovery of tumor lesions.

CONCLUSION

The economic impact of false-positive PET/CT results does not appear to be negligible and merits a genuine prospective medico-economic study.

Significance of F-18 FDG PET/MRI in the search for the etiology of inflammation of unclear origin and fever of unknown origin

PURPOSE

To evaluate the contribution of F-18 FDG-PET/MRI in the search for the etiology of the inflammation of unknown origin (IUO) and fever of unknown origin (FUO).

MATERIAL AND METHODS

The study included 104 patients who underwent F-18 FDG-PET/MRI for IUO or FUO. The sensitivity, specificity, predictive values of the PET/MRI findings in relation to the final diagnosis of IUO/FUO were evaluated. A five-point Likert scale was used to semiquantitatively assess the probability of the cause of IUO/FUO based on PET/MRI finding. Furthermore, clinical (fever, arthralgia, weight loss, night sweats, age) and laboratory (C-reactive protein, leukocytes) parameters were monitored and compared with the true positivity rate of PET/MRI.

RESULTS

In patients with definitively identified etiology of FUO and IUO, FDG-PET/MRI achieved a sensitivity of 96 %, specificity of 82 %, and positive and negative predictive values of 92 and 90 %. The cause of the IUO was determined in 71 patients (68.3 %). In 33 (31.7 %) patients, the etiology of IUO/FUO remained unknown, while in 25 (75.8 %) of them the symptoms resolved spontaneously and in 8 (24.2 %) patients they persisted without explanation even after 12 months of the follow-up. The most significant parameter in relation to subsequent PET/MRI finding was increased level of CRP, which was present in 96 % of true positive PET/MRI and normal CRP level was present in 56 % of true negative PET/MRI.

CONCLUSION

Based on this study, FDG-PET/MRI is a suitable alternative for the investigation of IUO/FUO, this imaging technique has a very high sensitivity and negative predictive value.

Rheumatology experience with FDG PET / CT in inflammation of unknown origin: a single - centre report for determining factors associated with diagnostic precision

BACKGROUND / AIM: The use of PET / CT is becoming more common in the elucidation of inflammatory processes in which the underlying cause cannot be determined by conventional examinations. Although PET / CT is an effective method for detecting inflammatory foci, the precise diagnosis may not be obtained in all cases. In addition, considering factors such as radiation exposure and cost, it becomes important to identify patients who can get results with PET / CT. In this study, it was aimed to examine the factors that can predict the differential diagnostic value of PET / CT by retrospectively scanning patients who underwent PET / CT for inflammation of unknown origin (IUO) in rheumatology practice.

METHODS

Demographic, clinical and laboratory information of the patients followed up in our clinic and who underwent PET / CT for differential diagnosis were enrolled. Whether they were diagnosed after PET / CT and during the follow - up period, and their diagnoses were examined.

RESULTS

A total of 132 patients were included in the study. A previous diagnosis of rheumatic disease was present in 28.8 % of the patients, and a history of malignancy was present in 2.3 % . The patients were divided into three groups: group 1 patients with increased FDG uptake in PET / CT and diagnosis confirmed by PET / CT, group 2 patients with increased FDG uptake in PET / CT but diagnosis was not confirmed, and group 3 patients without increased FDG uptake in PET / CT. Increased FDG uptake in PET / CT was detected in 73 % of the patients. While PET / CT helped the diagnosis in 47 (35.6 %) patients (group 1), it did not help the diagnosis in 85 (64.4 %) (groups 2 and 3). Thirty - one (65.9 %) of the diagnosed patients were diagnosed with a rheumatologic disease. When the 3 groups were compared, male gender, advanced age, CRP levels, presence of constitutional symptoms, SUVmax values and number of different organs with increased FDG uptake were higher in Group 1. Sixty - six percent and 74 % of the patients in groups 2 and 3 were not diagnosed during the follow - up period. No patient in group 3 was diagnosed with malignancy during follow - up.

CONCLUSION

PET / CT has high diagnostic value when combined with clinical and laboratory data in the diagnosis of IUO. Our study revealed that various factors can affect the diagnostic value of PET / CT. Similar to the literature, the statistically significant difference in CRP levels shows that patients with high CRP levels are more likely to be diagnosed with an aetiology in PET / CT. Although detection of involvement in PET / CT is not always diagnostic, there was an important finding that no malignancy was detected in the follow - up in any patient without PET / CT involvement. Key points • PET / CT is an effective method for detecting inflammatory foci. • PET / CT has proven to be effective in the diagnosis of rheumatological diseases, the extent of disease and the evaluation of response to treatment. • Indications for the use of PET / CT in the field of rheumatology and the associated factors and clinical features supporting the diagnosis with PET / CT are still to be fully clarified. • In routine practice, with PET / CT, both delays in diagnosis and examinations performed during diagnosis and the cost can be reduced.

Value of Positron Emission Tomography Coupled With Computed Tomography for the Diagnosis of Inflammatory Syndrome of Unknown Origin in an Internal Medicine Department

Objective

To evaluate the usefulness of positron emission tomography (PET) coupled with computed tomography (CT) in the diagnostic workup for inflammatory syndrome of undetermined origin (IUO) and to determine the diagnostic delay in an internal medicine department.

Patients and methods

We retrospectively studied a cohort of patients for whom a PET/CT scan had been prescribed in an indication of IUO in an internal medicine department (Amiens University Medical Center, Amiens, France) between October 2004 and April 2017. The patients were grouped according to the PET/CT findings: very useful (enabling an immediate diagnosis), useful, not useful, and misleading.

Results

We analyzed 144 patients. The median (interquartile range) age was 67.7 years (55.8-75.8 years). The final diagnosis was an infectious disease in 19 patients (13.2%), cancer in 23 (16%), inflammatory disease in 48 (33%), and miscellaneous diseases in 12 (8.3%). No diagnosis was made in 29.2% of the cases; half of the remaining had a spontaneously favorable outcome. Fever was observed in 63 patients (43%). Positron emission tomography coupled with CT was determined to be very useful in 19 patients (13.2%), useful in 37 (25.7%), not useful in 63 (43.7%), and misleading in 25 (17.4%). The median diagnostic delay (ie, the time interval between the first admission and a confirmed diagnosis) was significantly shorter in the useful (71 days [38-170 days]) and very useful (55 days [13-79 days]) groups than that in the not useful group (175 days [51-390 days]; P<.001). The median time interval between the PET/CT scan and the diagnosis was twice as long in the not useful group than that in the pooled misleading, useful, or very useful groups (P=.03). In a univariate analysis, the poor overall condition (P=.007) and the absence of fever (P=.005) were predictive of usefulness of PET/CT.

Conclusion

Positron emission tomography coupled with CT seems to be useful in the diagnosis of IUO and might shorten the diagnostic delay.

Higher diagnostic yield of 18F-FDG PET in inflammation of unknown origin compared to fever of unknown origin

OBJECTIVE

18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) is an important imaging technique in the workup of fever of unknown origin (FUO) and inflammation of unknown origin (IUO). Studies comparing the diagnostic yield of 18F-FDG PET between both entities are lacking.

METHODS

Retrospective analysis of FUO/IUO patients who underwent 18F-FDG PET between 2000 and 2019 in the University Hospitals of Leuven (Belgium). 18F-FDG PET images were assessed for accuracy and contribution towards the final diagnosis. Logistic regression was performed to evaluate the association between meeting FUO or IUO criteria and diagnostic contribution of 18F-FDG PET with and without adjustment for confounders.

RESULTS

Out of 604 patients, 439 (73%, mean age 56 years, 43% female) underwent 18F-FDG PET imaging, including 349 (79%) classified as FUO and 90 (21%) as IUO. Noninfectious inflammatory disorders were significantly more frequent in the IUO group (37% versus 25%; P = 0.03). 18F-FDG PET imaging had a sensitivity of 93% (89-96%), a specificity of 35% (29-42%), and made a positive contribution to the final diagnosis in 25% (21-29%) of cases. IUO was significantly associated with contributive 18F-FDG PET imaging compared to FUO (aOR 2.21 [95% CI 1.31-3.72]; P = 0.003). Among those with contributive 18F-FDG PET imaging, giant cell arteritis (IUO 25% versus FUO 12%) and polymyalgia rheumatica (IUO 17% versus FUO 1%) were numerically more frequent in the IUO group.

CONCLUSION

The diagnostic contribution of 18F-FDG PET was higher among those with IUO, most likely due to differences in diagnostic spectrum.

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.

Optimal use of the FDG-PET/CT in the diagnostic process of fever of unknown origin (FUO): a comprehensive review

Numerous studies have clarified the usefulness of ¹⁸F-fluorodeoxyglucose (FDG)-PET/CT (positron emission tomography) for diagnosing the cause of fever of unknown origin (FUO). Various types of disease can cause FUO, but the cause remains unknown in a certain proportion of FUO, even when the advanced diagnostic methodologies are used. FDG-PET/CT is regarded as a second-line modality in the diagnostic process of FUO, and its potential to identify the cause of FUO will be maximized when the appropriate clinical considerations are understood. Accordingly, this review presents basic knowledge regarding FUO, and reports the current status of FDG-PET/CT applied to diagnosing the cause of FUO, including diagnostic performance, test protocols, possible factors influencing the diagnostic result, outcomes, and cost-effectiveness. This knowledge will enable effective future use of FDG-PET/CT to improve outcomes in patients with FUO.

The Diagnostic Value of Fluoro-18 Fluorodeoxyglucose (F-18 FDG) PET/CT in Fever or Inflammation of Unknown Origin: A Retrospective Study at a Rheumatology Clinic

Introduction Further diagnostic procedures are necessary for patients with fever of unknown origin (FUO) and unknown cause of inflammation (inflammation of unknown origin - IUO) for the identification of the definitive diagnosis. The aim of this study was to evaluate the contribution and roles of F-18 FDG PET/CT (fluoro-18 fluorodeoxyglucose-positron emission tomography/computed tomography) in the diagnostic process of patients with FUO/IUO. Methods The data of 58 patients who had F-18 FDG PET/CT scans for FUO/IUO were re-evaluated retrospectively. The relationships between definitive diagnosis and fluorodeoxyglucose uptake and SUVmax (maximum standardized uptake value) were examined. Results  Rheumatic disease was diagnosed in 26 patients (44.5%), malignancy in 20 patients (34.5%), and infectious diseases in six patients (10.3%). The most prevalent rheumatic disease in patients with FUO/IUO was systemic vasculitis (n:10, 17.2%), especially large vessel vasculitis. There were 37 patients (63.7%) with clinically significant true positive fluorodeoxyglucose uptake. True positive fluorodeoxyglucose uptake was significantly higher in patients diagnosed with malignancy (85%, 17/20 patients) compared to other diagnoses. Fluorodeoxyglucose uptake above physiological levels was determined in 15 of the 26 patients (57.6%) diagnosed with rheumatic diseases. Conclusion The results of this study showed that F-18 FDG PET/CT is a useful imaging modality in FUO/IUO patients, who present a challenging diagnostic process for clinicians. In addition to malignancies, the presence of chronic inflammatory diseases, especially early period systemic vasculitis, were diagnosed in these patients.