Experimental pain sensitivity in opioid dependent patients: a preliminary examination of opioid-induced hyperalgesia

Prevalence data of pain in persons enrolled in or seeking treatment for opioid dependence have shown acute pain ranges of 48-80% and chronic pain (defined as lasting > 3 months) ranges of 24-61%. Growing evidence suggests that pronociceptive consequences result from long-term use of opioids. Opioid-induced hyperalgesia (OIH) is the paradoxical phenomenon of heightened pain sensitivity in individuals chronically exposed to opioids. The present analyses examined experimental pain sensitivity in opioid dependent (OD) persons without a current pain diagnosis. Eight OD participants from a residential study of opioid withdrawal were matched with Osteoarthritis (OA) participants with chronic knee pain and healthy controls (HC) on age, sex, and ethnicity (100% male; age x=49.17, SD= 4.25; Caucasian n=3, African American n=21). OA and HC participants were not on opioid medications. Quantitative sensory testing (QST) measures of pain threshold and pain modulation were completed. Results from a one-way ANOVA revealed statistically significant group differences on heat pain thresholds (F(2,17)=4.122, p < .05). Post-hoc tests revealed that both OD and OA participants had significantly lower heat pain thresholds compared to HCs (p<.05). The OD and OA participants did not significantly differ from one another. Although significant group differences did not emerge on other QST measures, trends were observed in which OA had the highest pain sensitivity, HC had the lowest and OD fell between the two. These preliminary analyses suggest OD individuals are more sensitive to experimentally induced pain compared to HC and demonstrate a comparable degree of thermal hyperalgesia similar to individuals with chronic knee OA pain. Further investigations with larger sample sizes are needed to validate these preliminary findings. Additional exploration of genetic, physiological and psychological factors that may account for these differences is necessary to help understand the mechanisms underlying the observed variability in response across groups.