Differential expression of cytokines in painful and painless neuropathies

Background: Pain is a common symptom in peripheral neuropathies. The factors determining why some peripheral neuropathies are painful and others are not are incompletely understood. Pro-inflammatory cytokines have been implicated to play a crucial role in the generation of pain. Objective: To investigate whether cytokine profiles differ between patients with painful or painless neuropathy. Methods: In this prospective study, we analyzed blood mRNA and protein levels of the pro-inflammatory cytokines interleukin-2(IL-2) and tumor necrosis factor-alpha(TNF) and the anti-inflammatory cytokines IL-4 and IL- 10 in 32 patients with painful neuropathy, 20 patients with painless neuropathy, and 38 healthy control subjects, using quantitative real-time PCR and ELISA. Results: Patients with a painful neuropathy had about twofold higher IL-2 mRNA (rho = 0.001) and TNF mRNA (p < 0.0001) and protein levels (rho = 0.009) than healthy control subjects and about twofold higher IL-2 and TNF mRNA (rho = 0.03; rho = 0.001) and protein levels (rho = 0.04; rho = 0.04) than patients with painless neuropathy. In contrast, mRNA levels of the anti-inflammatory cytokine IL-10 were about twofold higher in patients with painless neuropathy than in patients with painful neuropathy (rho = 0.001) and controls (rho = 0.004). IL-4 protein levels were 20-fold higher in patients with painless neuropathy (rho = 0.0001) and 17- fold higher in patients with painful neuropathy (p < 0.0001) than in healthy control subjects. Conclusions: A pro-inflammatory cytokine profile seems to be associated with pain in the setting of a peripheral neuropathy, corroborating findings in animal models with experimental painful neuropathies. This may have implications for future treatment strategies.