Elevated serum IFN-γand IFN-γ/IL-6 ratio in Kikuchi-Fujimoto disease

BACKGROUND: Kikuchi-Fujimoto disease (KFD) is typically a benign, self-limiting inflammatory disease. The diagnosis of KFD can be challenging for nonspecific symptoms, laboratory or imaging findings. In this study, we aimed to describe the clinical manifestations of patients with KFD and to access the potential role of serum cytokines in the diagnosis of this disease. METHODS: Patients with KFD were retrospectively enrolled from January 2015 to November 2021 at Shenzhen Children’s Hospital. Clinical data were collected from inpatient or outpatient medical records. Serum cytokines were detected by the Flowcytomix technique. Serum levels of cytokines were compared between patients with KFD and SJIA, or patients with KFD and KD. The data of patients without MAS were further analyzed. A receiver operating characteristic (ROC) curve analysis was further performed to access the potential role of serum cytokines in the diagnosis of KFD. RESULTS: Serum cytokines were detected in 25 (43.8%, 25/57) patients with a histological diagnosis of KFD. Compared to SJIA or KD patients, the KFD group had a significantly higher IFN-γ/IL-6 ratio and much lower levels of serum IL-6. The median level of serum IFN-γ in KFD was 41.65 pg/ml (range, 21.04–70.74 pg/ml), which was much higher than that in SJIA (median: 3.33 pg/ml, p = 0.16) or KD (median: 2.6 pg/ml, p = 0.01). After excluding patients with MAS, there was statistical significance in all comparisons of serum IFN-γ, IFN-γ/IL-6 ratio, and serum IL-6. The cutoff values of serum IFN-γ, IL-6, and IFN-γ/IL-6 ratio for differentiating KFD from SJIA were > 8.48 pg/ml, < 47.42 pg/ml, and > 0.45, respectively. The cutoff values of serum IFN-γ, IL-6, and IFN-γ/IL-6 ratio for differentiating KFD from KD were > 8.56 pg/ml, < 50.45 pg/ml, and > 0.45, respectively. The specificity of all those cutoff values for differentiating KFD from SJIA or KD was ≥ 94.7%. CONCLUSIONS: For patients with fever of unknown etiology and lymphadenopathy, after excluding HLH or MAS, serum IFN-γ > 8.56 pg/mL and IFN-γ/IL-6 ratio > 0.45 may highly suggest the diagnosis of KFD; serum IL-6 > 50.45 pg/mL indicates that the probability of KFD may be small, and sJIA, KD, and acute infection should be excluded first. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12969-023-00877-w.