Plasma pro-inflammatory markers and chronic neuropathic pain
Neuropathic pain, defined as pain caused by a lesion or disease of the somatosensory system is notoriously difficult to treat with available analgesics. Evidence-based guidelines emphasized on the use of topical lidocaine, certain antidepressants (e.g., tricyclics and duloxetine), gabapentinoids and possibly opioids. If better treatment strategies are to be developed, then the pathophysiology of different neuropathic pain conditions needs to be better understood.
Surgical procedures involving injury to nerves are associated with a high incidence of chronic post-surgical pain (CPSP). For example, thoracotomy often leads to nerve damage due to the use of rib retractors, and the prevalence of CPSP for this surgical procedure is as high as 30–40% 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.
To simultaneously investigate the plasma levels of chemokine interleukin 8 (IL-8) and the cytokines IL-6, IL-1β, and granulocyte macrophages 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), a study has been conducted. IL-6 was significantly higher in patients than in controls (0.92 ± 0.12 pg/ml vs. 0.57 ± 0.08 pg/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.
After the analysis, an increased level of IL-6 has been found in patients with neuropathic pain but not seen in the other pro-inflammatory substances which are investigated. There were several possible co-founders that were not registered or controlled for in this and other studies of neuropathic pain.