Classic fever of unknown origin: analysis of a cohort of 87 patients according to the definition with qualitative study criterion

Performance and value of 18F‑FDG PET/CT in patients with fever of unknown origin

Fever of unknown origin (FUO) is a common clinical and diagnostic challenge. The main aim of the present study was to evaluate the diagnostic accuracy of 18F-fluorodeoxyglucose (18FDG) positron emission tomography (PET)/CT in patients who present with FUO. Overall, 105 consecutive patients (61 men and 44 women) with a mean age of 51±35 years with FUO underwent 18FDG PET/CT scans. The performance of 18FDG PET/CT in determining the etiology of FUO was assessed. According to the PET/CT results, patients were classified into four groups: Group 1, patients with true-positive results (n=51; 49%), in whom abnormal 18FDG uptake identified the final diagnosis; group 2, patients with false-positive results (n=24; 23%), in whom 18FDG uptake was not consistent with the final diagnosis; group 3, patients with true-negative results (n=10; 9.5%), in whom the 18FDG uptake was normal and no final disease was established; and group 4, patients with false-negative results (n=20; 19%), in whom 18FDG uptake was normal and disease was finally established. Of the 51 patients with true-positive PET/CT results, 51% had infections, 35% had malignancies and 14% had inflammatory processes. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 72, 29, 68, 33 and 58%, respectively. In conclusion, the present results demonstrated that 18FDG PET/CT established the final diagnosis of FUO in the majority of patients (72%). These results support the use of 18FDG PET/CT in the initial evaluation and management of patients with FUO.

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.

Rheumatic disorders among patients with fever of unknown origin: A systematic review and meta-analysis

OBJECTIVES

To conduct a systematic literature review and meta-analysis to estimate the proportion of fever of unknown origin (FUO) and inflammation of unknown origin (IUO) cases that are due to rheumatic disorders and the relative frequency of specific entities associated with FUO/IUO.

METHODS

We searched PubMed and EMBASE between January 1, 2002, and December 31, 2021, for studies with ≥50 patients reporting on causes of FUO/IUO. The primary outcome was the proportion of FUO/IUO patients with rheumatic disease. Secondary outcomes include the association between study and patient characteristics and the proportion of rheumatic disease in addition to the relative frequency of rheumatic disorders within this group. Proportion estimates were calculated using random-effects models.

RESULTS

The included studies represented 16884 patients with FUO/IUO. Rheumatic disease explained 22.2% (95%CI 19.6 - 25.0%) of cases. Adult-onset Still's disease (22.8% [95%CI 18.4-27.9%]), giant cell arteritis (11.4% [95%CI 8.0-16.3%]), and systemic lupus erythematosus (11.1% [95%CI 9.0-13.8%]) were the most frequent disorders. The proportion of rheumatic disorders was significantly higher in high-income countries (25.9% [95%CI 21.5 - 30.8%]) versus middle-income countries (19.5% [95%CI 16.7 - 22.7%]) and in prospective studies (27.0% [95%CI 21.9-32.8%]) versus retrospective studies (20.6% [95%CI 18.1-24.0%]). Multivariable meta-regression analysis demonstrated that rheumatic disease was associated with the fever duration (0.011 [95%CI 0.003-0.021]; P=0.01) and with the fraction of patients with IUO (1.05 [95%CI 0.41-1.68]; P=0.002).

CONCLUSION

Rheumatic disorders are a common cause of FUO/IUO. The care of patients with FUO/IUO should involve physicians who are familiar with the diagnostic workup of rheumatic disease.

Diagnostic value of F-18 FDG PET/CT in fever or inflammation of unknown origin in a large single-center retrospective study

Cause determination is challenging in fever or inflammation of unknown origin (FUO/IUO) despite today’s diagnostic modalities. We evaluated the value of F-18 FDG PET/CT in an unselected patient collective. This retrospective nonrandomized single-center study enrolled 300 male and female patients with FUO/IUO. PET/CT findings were compared with final clinical outcomes to determine the sensitivity, specificity, clinical significance, etiological distribution of final diagnoses, impact on treatment, role of white-blood cell count (WBC), and C-reactive protein (CRP). In 54.0% (162/300) PET/CT was the decisive exanimation for establishing the final diagnosis, in 13.3% (40/300) the findings were equivocal and indecisive, in 3.3% (10/300) PET/CT findings were false positive, while in 29.3% (88/300) a normal F-18 FDG pattern was present. Statistical analysis showed a sensitivity of 80.2% and a specificity of 89.8% for the contribution of PET/CT to the final diagnosis. CRP levels and WBC were not associated with PET/CT outcome. PET/CT let to new treatment in 24.0% (72/300), treatment change in 18.0% (54/300), no treatment change in 49.6% (149/300), and in 8.3% (25/300) no data was available. Our study demonstrates the utility of F-18 FDG PET/CT for source finding in FUO/IUO if other diagnostic tools fail.