Background and methods: Proinflammatory cytokines play an important role in the pathophysiology of neuropathic pain syndromes. The objective of this study was to evaluate plasma levels of proinflammatory cytokines before and after treatment with tramadol in patients with herniated intervertebral disks and carpal tunnel syndrome, and to compare them with normal individuals.
Methods: Thirty-eight patients with neuropathic pain secondary to herniated intervertebral disks or carpal tunnel syndrome participated in this study. All patients were treated with controlled release tramadol (100 mg every 12 hours) for 10 days. Venous blood (5 mL) was collected in the morning, before treatment and on the 11th day, and stored (-70 degrees C) until analysis. ELISA was used to determine the plasma levels of cytokines (TNF-+/-, IL-1, IL-6) and receptors sTNF-R1 (R & D Systems). Plasma levels of cytokines of 10 healthy volunteers were also determined.
Results: The concentration of TNF-+/- before (5.8 +/- 2.8 pg.mL-(1)) was significantly higher than after treatment with tramadol (4.8 +/- 2.1 pg.mL-1; p = 0.04, Mann-Whitney test). The levels of IL-1(2), IL-6, and sTNF-R1 before and after treatment with tramadol showed no significant differences. Plasma levels of TNF-+/- (healthy individuals: 1.4 +/- 0.5; pain patients: 5.8 +/- 2.8 pg.mL-1; p = 0.01) and IL-6 (healthy individuals: 1.2 +/- 0.8; pain patients: 3.5 +/- 2.6 pg.mL-1; p = 0.01) were significantly higher in patients with neuropathic pain, Mann-Whitney Test.
Conclusions: In patients with herniated intervertebral disks and carpal tunnel syndrome, plasma levels of TNF-+/- and IL-6 were higher than in healthy volunteers, while differences in the concentrations of sTNF-R and IL-1(2) were not observed. Plasma levels of TNF-+/-, but not of IL-6, sTNF-R, and IL-1(2), decreased after treatment with tramadol (100 mg every 12 hours).