Preliminary Study of the Plasma and Cerebrospinal Fluid Concentrations of IL-6 and IL-10 in Patients with Chronic Pain Receiving Intrathecal Opioid Infusions by Chronically Implanted Pump for Pain Management

Objective. This preliminary study assessed possible relationships between plasma and/or cerebrospinal fluid (CSF) concentrations of the pleiotropic cytokine, interleukin (IL)-6, the anti-inflammatory cytokine, IL-10, and levels of pain reported by patients receiving intrathecal (i.t.) opioids. Design. A prospective study quantifying IL-6 and IL-10 concentrations using enzyme-linked immunoassays in samples of plasma and CSF as well as assessment of pain scores in patients receiving intrathecal opioids for management of chronic noncancer pain. Setting. Outpatient pain clinics. Patients. Patients with chronic pain receiving intrathecal morphine or hydromorphone alone or in combination with local anesthetics. Interventions. Two groups of patients were studied. The first group (n = 50) had been receiving long-term i.t. opioids by chronically implanted pump for similar to 5 years; paired samples of plasma and CSF were collected at the time of i.t. pump refill. For the second patient group (n = 10), possible temporal changes in the plasma and/or CSF concentrations of IL-6 and IL-10 were investigated for 3 months after initiation of i.t. opioid infusions. Results. For patients receiving long-term i.t. opioid infusions, there were significant inverse correlations (P < 0.05) between pain intensity and the plasma (but not CSF) IL-10 and IL-6 concentrations. Despite the considerable inter-patient variability in the CSF concentrations of IL-6 in the long-term cohort, the mean CSF IL-6 concentration was approximately fivefold higher in patients receiving long-term i.t. opioids relative to those receiving i.t. opioids for only 3 months. Conclusions. The significant inverse correlations observed between pain intensity and the plasma IL-6 and IL-10 concentrations in patients receiving longterm i.t. opioids for chronic pain management, suggests that these cytokines are worthy of further investigation as possible biomarkers of persistent pain.