Objective To investigate the imaging features and diagnostic value of ¹⁸F-fluorodeoxyglucose (FDG) PET/CT in differentiating adult-onset Still’s disease (AOSD) from lymphoma in patients with fever of unknown origin (FUO).

Methods A retrospective analysis was conducted on 295 patients (103 males, 192 females; mean age 42.9±16.1 years) who underwent ¹⁸F-FDG PET/CT for FUO at Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, between December 2016 and December 2018. 69 AOSD patients and 36 lymphoma patients were included. Metabolic parameters of bone marrow, spleen, and lymph nodes on ¹⁸F-FDG PET/CT were compared between the two groups using chi-square tests or independent-sample t-tests.

Results The incidence of ¹⁸F-FDG hypermetabolism in bone marrow 62.3% (43/69) vs. 16.7% (6/36), χ²=28.4, P<0.001 and maximum standardized uptake value (SUV_max) (5.5±1.8 vs. 4.2±1.2, t=5.1, P<0.001) were significantly higher in AOSD patients than in lymphoma patients. Although the incidence of splenomegaly was lower in AOSD patients than in lymphoma patients 37.7% (26/69) vs. 61.1% (22/36), χ²=6.3, P=0.011, there was no significant difference in spleen SUV_max between the two groups (4.3±1.7 vs. 4.1±2.6, t=0.9, P=0.344). AOSD patients exhibited lower lymph node SUV_max (6.2±5.7 vs. 10.9±8.8, t=−3.1, P=0.003), total metabolic lesion volume (total MLV: (33.5±49.2) cm³ vs. (80.3±399.2) cm³, t=−4.9, P<0.001), and total lesion glycolysis (total TLG: (167.0±544.6) g vs. (1304.0±3534.5) g, t=−4.3, P<0.001) compared to lymphoma patients.

Conclusions ¹⁸F-FDG PET/CT can assist in differentiating AOSD from lymphoma as causes of FUO based on differences in features such as the incidence of bone marrow hypermetabolism, the incidence of splenomegaly, and the total metabolic lesion volume (MLV) and total lesion glycolysis (TLG) of hypermetabolic lymph nodes.