A cohort study comparing the serum levels of pro- or anti-inflammatory cytokines in patients with lumbar radicular pain and healthy subjects

The factors influencing the presence or absence of pain in sciatica secondary to disc herniation remain incompletely understood. We hypothesized that the imbalance in inflammatory cytokines is implicated in the generation of pain. In our study, serum levels of pro-inflammatory and anti-inflammatory cytokines were investigated among patients with severe sciatica; the serum levels were compared with those of patients with mild sciatica and healthy subjects.

In this prospective study, blood protein levels of the pro-inflammatory cytokines, namely, interleukin-6 (IL-6), interleukin-8 (IL-8),and tumor necrosis factor-α (TNF-α), and the anti-inflammatory cytokines, namely, interleukin-4 (IL-4) and interleukin-10 (IL-10), of 58 patients with severe sciatica, 50 patients with mild sciatica, and 30 healthy control subjects were analyzed through ELISA. Physical and mental health symptoms were determined using the Oswestry Disability Index (ODI) and short form-36 (SF-36) questionnaire. Spearman rank correlation coefficient was also determined to calculate the correlation between the scores obtained from the questionnaires and the serum levels of cytokines.

IL-6 protein was detected in the three groups and median levels were about 1.5 times higher in patients with severe sciatica than the mild sciatica group (p = 0.02) and the controls (p = 0.03). Median levels of IL-8 in sciatica patients were higher than those of the healthy controls (p = 0.001 for severe sciatica, p = 0.02 for mild sciatica). The TNF-α protein values were approximately twofold higher in the severe sciatica group than in the mild sciatica group (p < 0.01) and in the healthy control group (p < 0.01). Median levels of IL-4 were about 2.5-fold higher in mild sciatica (p < 0.01) and about twofold higher in patients with severe sciatica (p = 0.012) when compared with controls. Median protein levels of IL-10 showed a trend to be higher in patients with mild sciatica compared with severe sciatica (p < 0.01) and with healthy controls (p < 0.01). ODI was significantly correlated with IL-6 (r = 0.394, p = 0.013), TNF-α (r = 0.629, p < 0.001), and IL-10 (r = −0.415, p = 0.009). ODI was not significantly correlated with IL-4 (r = −0.174, p = 0.29) and IL-8 (r = −0.133, p = 0.418).

These findings support our hypothesis that sciatica pain is accompanied by the imbalance in inflammatory cytokines.