The Etiology Diagnostic Application Of¹⁸F-FDG PET/CT In Patients With Fever Of Unknown Origin

Objective:¹⁸F-FDG PET/CT imaging results and Clinical data of patients with fever of unknown origin（FUO）were analyzed retrospectively to explore the value of PET/CT in the etiology diagnosis of FUO.Methods:The clinical and imaging data of 108 FUO patients who underwent ¹⁸F-FDG PET/CT scan in Hebei People’s Hospital from September 2013 to August 2019 were analyzed retrospectively.The diagnosis were based on biopsy,The final diagnosis of the people without biopsy will be made based on the results of laboratory inspections or clinical treatment,and these patients were combined with at least 3 months of follow-up to ensure the reliability of the diagnosis.According to the final etiological of FUO,the proportion of infection,malignancy,rheumatologic disease and unknown were analyzed.The sensitivity,specificity,positive predictive value,negative predictive value and accuracy of PET/CT for the diagnosis of different causes of FUO were evaluated respectively（The malignancy was divided into hematologic malignancy and non-hematologic malignancy）.The maximum standardized uptake value(SUV_max)and the visual rating scale（the metabolic intensity of lesions was compared with the metabolic of mediastinal blood pool,and divided into 0～3 points）were used to analyze the uptake intensity of ¹⁸F-FDG in the lesion.The t test was used to compare the SUV_maxdifferences between groups that conform to the normal distribution;The Mann-whitney u test was used to compare the differences of SUV_maxand visual analysis grade data between groups that did not conform to normal distribution.Difference was considered statistically significant when P<0.05.Results:Among all 108 FUO patients,the final diagnosis were established in 84.3%（91/108）patients and 15.7%（17/108）patients were still unknown origin.The patients who were established final diagnosis including 41.8%（38/91）patients causes for infectious diseases,22.0%（20/91）causes for malignancies,34.1%（31/91）with rheumatologic diseases,2.2%（2/91）with miscellaneous diseases.The PET/CT images were positive in 105 cases,with a positive rate of 97.2%.The PET/CT had a sensitivity of 96.6%,specificity of 2%,positive predictive value of53.3%,negative predictive value of 33.3%and accuracy of 52.8%.The sensitivity of PET/CT in diagnosing FUO caused by infection was 96.4%and the accuracy was 71.1%.PET/CT diagnosis of malignant tumor causes FUO sensitivity 100%,accuracy 75%;The sensitivity and accuracy of PET/CT imaging in diagnosing rheumatologic diseases were 100%and48.4%respectively.The PET/CT images of 38.0%（41/108）patients showed nonspecific abnormal uptake（NAU）,the most one etiology is rheumatologic diseases 39.0%（16/41）.The SUV_maxof the malignant tumor lesion was significantly different from the rheumatic disease（10.0±4.5 vs 6.4±2.3;t=3.269,P<0.01）.There were no significantly different between malignant tumor and infectious diseases lesion in SUV_max（10.0±4.5 vs 8.4±4.1;Z=-1.028,P>0.05）.The SUV_maxof the non-hematologic malignancy lesion was significantly different from the rheumatic disease（12.7±2.9 vs 6.4±2.3;t=5.082,P<0.001）.The SUV_maxof the non-hematologic malignancy lesion was significantly different from the infectious diseases（12.7±2.9 vs 8.4±4.1;Z=-2.065,P<0.05）.The SUV_maxof the infectious diseases lesion was significantly different from the rheumatic disease（8.4±4.1 vs 6.4±2.3;Z=-2.149,P<0.05）.Visual analysis rating scale was used for analysis,There were no significantly different between malignant tumor and rheumatic disease（2.7±0.7 vs 2.3±0.8;Z=-1.951,P>0.05）.There were no significantly different between infectious diseases and malignant tumor lesion（2.5±0.8vs 2.7±0.7;Z=-0.995,P>0.05）.There were no significantly different between non-hematologic malignancy and rheumatic disease（3.0±0.0 vs2.3±0.8;Z=-1.745,P>0.05）.There were no significantly different between non-hematologic malignancy and infectious diseases（3.0±0.0 vs 2.5±0.8;Z=0.188,P>0.05）.There were no significantly different between infectious diseases and rheumatic disease（2.5±0.8 vs 2.3±0.8;Z=-1.195,P>0.05）.Conclusion:The etiology of FUO was infectious diseases,rheumatic disease and malignancy.¹⁸F-FDG PET/CT can provide valuable information for diagnosis of FUO.With high sensitivity,it has certain value in the qualitative diagnosis of benign and malignant lesions.The SUVmax of malignant tumor lesions is higher than that of rheumatic diseases,while the SUVmax of non-hematological tumor lesions is higher than that of infection and rheumatic diseases.The features of the whole body scan have special advantages in identifying and locating potential lesions.The NAU image in PET/CT have implications for diagnosing the rheumatologic diseases,and it is helpful to exclude local lesions.The visual score analysis can make a simple analysis of the nature of the lesions,but it is still necessary to measure the SUVmax and combine with the distribution of the lesions that can accurately measure the metabolism of the lesions.