Elevated IL-1β and IL-6 levels in lumbar herniated discs in patients with sciatic pain

Previous experimental models have shown that proinflammatory cytokines modulate peripheral and central nociception. However, the direct correlation between inflammation and pain in patients remains unclear. Our aim is to correlate the levels of inflammation in the spine with pre- and postoperative pain scores after discectomy.

Paravertebral muscle, annulus fibrosus (AF) and nucleus pulposus (NP) biopsies were intraoperatively collected from ten lumbar disc hernia (LDH) patients suffering from chronic sciatic pain and, as painless controls, five scoliosis patients. IL-1β and IL-6 expressions in these biopsies were assessed by qPCR and western blot. The amount of pain, indicated on a 0-10 point visual analogue scale (VAS), was assessed 1 day before surgery and 6 weeks and 1 year after surgery. For analysis purposes, LDH patients were grouped into painful (VAS ≥ 3.5) and non-painful (VAS < 3.5). LDH painful patient group showed a onefold increased mRNA expression of IL-1β in the NP, and IL-6 in the AF and NP (p < 0.05 vs. controls).

By western blot analysis, both cytokines were clearly visible in all LDH biopsies, but not in controls. However, cytokine expression of the painful patient group did not differ from those of the non-painful patient group. In addition, there was no correlation between VAS scores and either marker.

These findings support the idea that LDH is accompanied by a local inflammatory process. Yet, the lack of correlation between IL-1β or IL-6 expression and the severity pain suggests that these cytokines may not play a leading role in maintaining a pain generating network.