Association between serum interleukin-17 levels and ectopic bone formation in OPLL patients with DISH.

ABSTRACT

OBJECTIVE: To investigate the relationship between the severity and morphology of heterotopic ossification in the spinal ligaments including sacroiliac (SI) joints, and serum interleukin-17 (IL-17) levels in patients with ossification of the posterior longitudinal ligament (OPLL) with or without diffuse idiopathic skeletal hyperostosis (DISH), as well as a non-OPLL group. METHODS: A total of 103 patients with OPLL (DISH (-), n = 50; DISH (+), n = 53) and 53 age- and gender-matched controls were included. The serum levels of IL-17 were analyzed, and the severity of ectopic ossification and the morphology of ectopic bone formation were evaluated. The SI joint morphological variations were categorized into four types. RESULTS: No significant differences were found in serum IL-17 levels between the OPLL and control groups. However, the DISH (+) group showed higher IL-17 levels than the DISH (-) group, especially in female patients (p = 0.003). Additionally, IL-17 levels were positively correlated with the number of Flat vertebral units, meaning one of the characteristics of DISH ossification type (R2 = 0.199, p = 0.012). IL-17 levels in type 4 were significantly higher in the DISH (+) group than in the DISH (-) group. CONCLUSIONS: The morphological characteristics of paravertebral bone formation in the entire spine, including the SI joint, are likely associated with serum IL-17 levels in OPLL. These findings provide pathological and serological evidence of local inflammation contributing to paravertebral ossification of OPLL patients.