Diagnostic Value Of ¹⁸F-FDG PET/CT Imaging In Patients With Fever Of Unknown Origin

Objective:To analyze the etiological distribution of patients with fever of unknown origin and the characteristics of ¹⁸F-FDG PET/CT in different category of diseases,and to explore the diagnostic value of ¹⁸F-FDG PET/CT in patients with fever of unknown origin.Methods:A total of 141 patients who met the inclusion criteria for fever of unknown origin and received ¹⁸F-FDG PET/CT examination from China-Japan Union Hospital of Jilin University from January 2019 to August 2021 were included.The final etiological diagnosis of the patients was determined by clinicians based on clinical manifestations,imaging,histopathological examination,laboratory and etiological examination,and follow-up.The final etiological diagnosis was classified into infections,malignancies,rheumatologic diseases,miscellaneous causes and cause unknown.To observe the ¹⁸F-FDG PET/CT imagings,both local high uptake lesion and nonspecific abnormal uptake（NAU）were positive.To analyze the characteristics of ¹⁸F-FDG PET/CT in different category of FUO,¹⁸F-FDG uptake was quantitatively and visually evaluated by using SUVmax and a 4-grade scale respectively.Elliptic regions of interest（ROI）was drawn on PET/CT fusion images to perform semi-quantitative analysis of ¹⁸F-FDG uptake to obtain SUVmax values.In the semi-quantitative analysis of high uptake lesion,the measurement range was the primary lesion.In the semi-quantitative analysis of NAU,if a homogeneous high uptake was found in spleen,a spheroid ROI with diameter of 3.0 cm was drawn in spleen parenchyma,and if a homogeneous high uptake found in bone marrow,a cuboid ROI was drawn containing lumbar vertebraes 3 to 5.When PET/CT images were negative,a spherical ROI with a diameter of 3.0cm was drawn in the soft tissue background.Visual evaluation with a 4-grade scale(grade 0:¹⁸F-FDG uptake lower than the soft tissue background;grade 1:equivalent to the soft tissue background;grade 2:higher than soft tissue background;and grade 3:very strong uptake)for evaluation of lesion uptake.The significance of PET/CT in diagnosing of FUO was evaluated by questionnaire survey among clinicians.Details are as follows:（1）did PET/CT provide valuable diagnostic information?（yes or no）;（2）did PET/CT imaging have a clinical impact on clinical decisions?（grade 0:PET/CT findings was wrong and caused confusion;grade 1:PET/CT findings did not affect clinical decisions;grade 2:PET/CT findings did not change but increased the certainty of clinical decisions;and grade 3:PET/CT findings changed the clinical decision）,grade 2 and 3 were considered to benefited from PET/CT.SPSS 25.0 software was used for statistical analysis.Measurement data were described as`x±s,and counting data were expressed as percentage.Kruskal-wallis H test was used for correlation analysis of SUVmax and visual score for different category of diseases.p<0.05 was statistically significant.Results:Among 141 patients,63（44.7%）were diagnosed as infections,41（29.1%）as malignancies,21（14.9%）as rheumatologic diseases,and 3（2.1%）as miscellaneous causes.After 3-6 months of follow-up,13 patients（9.2%）cases were still unable to identify the etiology.On PET/CT examinations,127（90.1%）of the patients had a positive finding,of which 117（83.0%）had found local high uptake lesion,47（33.3%）had found NAU,and 37（26.2%）had found both local high uptake lesion and NAU.Among 10（7.1%）patients,NAU was the only positive finding on PET/CT images.Malignancies（100%）and infectious diseases（98.4%）were mainly manifested as local high uptake lesion,while rheumatologic diseases were mainly manifested as NAU,and the percentage of NAU in rheumatologic diseases was the highest,about 57.1%（12/21）.The SUVmax of malignancies was 16.96±9.72,while that of infections,rheumatologic diseases,miscellaneous causes and cause unknown was 9.68±5.6,6.84±4.89,1.43±1.45 and 3.44±4.43,respectively,SUVmax of malignancies was higher than that of other category diseases,and the difference was statistically significant（p<0.05）;the visual score of malignancies was 2.8±0.4,while that of infections,rheumatologic diseases,miscellaneous causes and cause unknown was 2.4±0.5,2.0±1.0,0.7±1.2 and 0.7±1.1 respectively,visual scores of malignancies was higher than that of other category diseases,and the difference was statistically significant（p<0.05）.Clinical questionnaire showed that,of 141 patients,¹⁸F-FDG PET/CT provided valuable information for the diagnosis of 112 patients（79.4%）,including 62 infections,41 malignancies,and 9 rheumatologic diseases.Based on the impact of PET/CT on clinical decision making for FUO,126 patients（89.4%）benefited from PET/CT examination.Conclusion:In this study,¹⁸F-FDG PET/CT has a high diagnostic value for patients with fever of unknown origin,with 89.4%of patients benefited from PET/CT.The proportion of nonspecific abnormal uptake in ¹⁸F-FDG PET/CT images was the highest in rheumatologic diseases and had a positive impact on clinical decision making.In ¹⁸F-FDG PET/CT images,the SUVmax and visual score of malignancies were higher than those of other category of diseases.