The role of cytokines and chemokines in the maintenance of chronic pain-a pilot study.

Abstract

The immune system is believed to be important in the initiation and maintenance of chronic pain. The aim was to investigate whether patients with chronic painful polyneuropathy (PP) differ in cytokine profiles of serum and/or cerebrospinal fluid (CSF) compared with pain-free controls. Thirty-nine patients (16 women and 23 men, mean age, 69.2 ± 12.7 years, range 41-92 years) with PP (mean duration 43 ± 48.3 months) were phenotyped with quantitative sensory testing and electroneurography, and serum and CSF samples were analyzed by 40-multiplexed, bead-based cytokine immunoassays. Results were compared with 36 age- and gender-matched patients with normal pressure hydrocephalus and absence of abnormal CSF findings. Compared with controls, patients with PP had lower concentrations of several proinflammatory and anti-inflammatory chemokines and cytokines in CSF, and others showed the same tendency, among these were tumor necrosis factor-α (14.1 ± 10.0 vs 23.9 ± 16.4 pg/mL, P < 0.005), interleukin (IL)-2 (0.6 ± 0.4 vs 1.2 ± 0.6 pg/mL, P < 0.0001), IL-6 (4.7 ± 6.8 vs 7.3 ± 9 pg/mL, P = 0.001), and IL-10 (7.5 ± 6.8 vs 16.8 ± 19.2 pg/mL, P < 0.01), whereas no differences were observed in serum. Results suggest that (1) inflammatory mediators play a minor role in the maintenance of chronic pain in contrast to initiation of acute pain, (2) chemokines/cytokines are downregulated in chronic pain, or (3) chemokines/cytokines have a protective role for nerve regeneration that is disturbed in patients with chronic pain.