(263) Less Efficient Endogenous Inhibition of Spinal Nociception Predicts Chronic Pain Onset: A Prospective Analysis from the Oklahoma Study of Native American Pain Risk (OK-SNAP)

Abstract

Chronic pain results in tremendous economic and psychological burden. Thus, an ability to identify individuals at risk for chronic pain onset could be an important first step in reducing this burden. One mechanism that may contribute to pain onset is impaired descending pain inhibition. The present study examined whether the efficiency of descending inhibition (as measured by conditioned pain modulation, CPM) predicted future chronic pain onset in a sample of participants who were healthy and pain-free at the time of enrollment in OK-SNAP. Chronic pain onset was determined prospectively from follow-up surveys administered every 6-months following enrollment. Of the 139 Native American (NA) and 147 non-Hispanic white (NHW) participants enrolled, 208 (73%) responded to ≥1 follow-up. Participants were said to have developed chronic pain if they experienced persistent pain for >3 months and the pain did not remit at subsequent follow-ups (N=34, 16%). 174 persons did not develop chronic pain. CPM was assessed from painful electric stimulations delivered before and during hand/forearm submersion in 10˚C water. Pain ratings and nociceptive flexion reflexes (NFR; correlate of spinal nociception) were assessed in response to electric stimuli. CPM efficiency = change in pain/NFR. CPM of pain and NFR were entered as predictors in a logistic regression that controlled for race (NA vs. NHW), age, BMI, sex, general health, depression, anxiety, and somatization. Interactions between race and CPM efficiency were examined as well. Results found less efficient CPM of NFR (OR=6.53, 95%CI: 1.04, 40.95) and more depressive symptoms (OR=10.22, 95%CI: 1.28, 81.36) at enrollment predicted chronic pain onset. The model explained 34.5% of the variance (Nagelkerke R2=.345). Interactions of CPM variables with race were not significant. These findings imply that impaired descending inhibition of spinal nociception (NFR) may play a role in the development of chronic pain.