Elevated IL-6 levels correlate with the development of intervertebral disc degeneration: a case-control study and meta-analysis

Objectives: We aimed to investigate the correlation between serum IL-6 levels and the development of intervertebral disc degeneration (IDD) by conducting a case-control study and meta-analysis. Methods: Between January 2013 and December 2014, 87 IDD patients hospitalized in 307 Hospital of PLA, were regard as the case group and divided into bulging, protrusion and sequestration IDD types. The other 23 traumatic lumbar fracture patients who have received operations were identified as the control group. Visual analog scale (VAS) and Oswestry disability index (ODI) were used for pain and low back, lower limb dysfunction pre-operatively. The IL-6 levels in nucleus pulposus of intervertebral disc was measured by enzyme-linked immunoassay (ELISA). All relevant casecontrol studies were retrieved under stringent exclusion and inclusion criteria. R 3.1.0 software was applied for data analysis. Result: Our study showed thatthe IL-6 levels in the case group were evidently higher compared to the control group (all P < 0.05), and the highest IL-6 levels were observed in sequestration IDD type. The highest and lowest VAS and ODI score were respectively found on sequestration and bulging IDD patients. Results of metaanalysis also revealed significant correlation between IDD and serum IL-6 levels (SMD = 3.47, 95% CI = 1.73-5.22, P < 0.001). Serum IL-6 levels were also found to be correlated with the three IDD types (bulging: SMD = 2.41, 95% CI = 1.71-3.11, P < 0.001; protrusion: SMD = 3.27, 95% CI = 2.57-3.96, P < 0.001; sequestration: SMD = 7.33, 95% CI = 5.93-8.74, P < 0.001). Conclusion: Our findings suggest that elevated IL-6 levels may correlate with the progression of IDD.