Plasma pro-inflammatory markers in chronic neuropathic pain: A multivariate, comparative, cross-sectional pilot study

BACKGROUND: Caused by a lesion or disease of the somatosensory system, neuropathic pain is notoriously difficult to treat with conventional analgesics. It has been suggested that inflammatory cytokines play a role in the development and maintenance of neuropathic pain. But human studies of these substances are relatively few and partly contradictory. OBJECTIVES: To simultaneously investigate the plasma levels of chemokine interleukin 8 (IL-8) and the cytokines IL-6, IL-1β, and Granulocyte macrophage colony-stimulating factor (GM-CSF) in patients with peripheral neuropathic pain (most of whom due to failed back surgery syndrome) (n=14) compared to controls (n=17). RESULTS: IL-6 was significantly higher in patients than in controls (0.92±0.12pg/ml vs. 0.57±0.08pg/ml, p=0.012). IL-1β, IL-8, and GM-CSF levels did not differ between the two groups. A multivariate analysis showed a tendency for patients also to have higher GM-CSF plasma levels than controls. CONCLUSIONS: This study found an increased level of IL-6 in plasma in patients with neuropathic pain, but not for the other pro-inflammatory substances investigated. There are several possible confounders not registered or controlled for in this and other studies of neuropathic pain. IMPLICATIONS: Larger studies that take several possible confounders into consideration are needed to further investigate the levels of plasma cytokines in different pain conditions.