Endogenous Pain Modulation in Low Back Pain

Abstract

A significant driver of pain in low back pain (LBP) is alteration to endogenous pain modulation (EPM). EPM can be measured using quantitative sensory tests (QST), which provides important information on nociceptive pathways. Exercise therapy is recommended as the first line of care for LBP; however, there is limited information on the mechanisms of action that lead to symptom improvements. The first manuscript was a scoping review that summarized protocols used to assess EPM using QST such as pain pressure threshold (PPT), temporal summation (TS), conditioned pain modulation (CPM) or exercise-induced hypoalgesia (EIH) in LBP. Scientific databases were searched for articles that used QST or EIH protocols in LBP. In total, 193 studies were included in this review: 172 used PPT, 54 used TS and 53 used CPM and 5 investigated EIH. There was high variability in the type of equipment, timing, trials, and testing location with many studies not reporting this information. The results demonstrate a need for standardized protocols and reporting guidelines as well as further research to aid in selecting the most appropriate QST parameters for different clinical presentations. The second manuscript was a pilot study that assessed the feasibility of a protocol investigating if changes in EPM occur after exercise therapy. Participants were recruited through a larger trial (WELBack) and were randomized to receive one of two exercise therapies. Participants attended two testing sessions (before and after an 8-week treatment) consisting of PPT, TS, CPM and EIH. Thirty-six participants were recruited and completed baseline assessments. In total, 32 (88.9%) participants completed the follow-up assessment. The results demonstrated that the protocol was feasible. Improvements to patient reported outcomes were seen, but not to all EPM measures. Future work should consider changes to the CPM protocol, and a fully powered study to investigate EPM changes after exercise therapy.