FDG PET/CT used in identifying adult-onset Still's disease in connective tissue diseases

To explore the ¹⁸F-fluoro-dexoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) imaging characteristics of adult-onset Still's disease (AOSD) and its significance in differential diagnosis from other connective tissue diseases (CTDs).

FDG PET/CT images of 54 patients with AOSD and 66 with other CTD from patients suffering from fever of unknown origin (FUO) were retrospectively studied and compared with 40 healthy controls. Clinical and PET/CT characteristics of AOSD and other CTDs were compared, and SUV_max (maximum standardized uptake value) was used to analyze the differences of FDG uptake in the blood pool, liver, spleen, bone marrow, and hyperplastic lymph nodes between the AOSD and other CTDs. The SUV_max ratios of the spleen, bone marrow, and lymph nodes to the liver were used to establish the diagnostic criteria for differential diagnosis of AOSD, and its diagnostic efficiency was evaluated.

Positive findings are presented in 53/54 (98.1%) AOSD patients and 61/66 (92.4%) other CTD patients in PET/CT imaging. AOSD manifested as diffusely increased FDG uptake in the spleen and bone marrow, and multiple reactive hyperplasia lymph nodes are symmetrically distributed mainly in the neck and axilla, while other organs were seldom involved. Although these abnormalities could be seen in other CTDs, its incidence and uptake value were both higher in AOSD. If two or more of the following three standard were met, the sensitivity, specificity, and accuracy of diagnosing AOSD could reach 90.7%, 92.4%, and 91.7%, respectively: ① spleen SUV_max/liver SUV_max ≥ 1.2 and/or bone marrow SUV_max/liver SUV_max ≥ 1.4; ②symmetrically distributed reactive hyperplastic lymph nodes mainly in the neck and axilla with a lymph node SUV_max/liver SUV_max ≥ 1.8; and ③ no other abnormal uptake found in other organs.

Characteristic manifestations in AOSD were found on FDG PET/CT. These findings could help to identify AOSD from the other CTDs, especially in cases of fever of unknown origin, where it can assist in identifying the cause. Key Points • Image characteristics of FDG PET/CT in adult-onset Still's disease were described. • FDG PET/CT helps in identifying adult-onset Still's disease from the other connective tissue diseases. • FDG PET/CT imaging standard for diagnosing adult-onset Still's disease were established.