Conditioned Pain Modulation in Chronic Low Back Pain: A Systematic Review of Literature

Objective: The objective of the review is to determine whether conditioned pain modulation (CPM) is impaired in adults with chronic low back pain (CLBP) when compared with pain-free individuals. Methods: A a systematic search of the literature was undertaken using the databases: MEDLINE, Scopus, CINAHL and Web of Science. The citations of included studies were reviewed for additional studies. Observational, cross-sectional, case-control studies published in English between January 1990 and August 2019 were considered. Studies that investigated the efficiency of standardized CPM regimens among defined cases of CLBP and in comparison, with pain-free controls were included. After initial title and abstract screening, 2 authors reviewed the full texts of the eligible articles independently. Risk of bias was carried out using assessment of 4 categories: blinding of the outcome assessors, representativeness of cases to the specified population, comparability of cases and controls, and control of confounding variables. Results: In total, 643 records were identified, of which 7 studies were included. Overall, the results of the studies reported mixed conclusions on the efficiency of CPM in CLBP. Three studies identified significant differences for CPM between CLBP and pain-free controls and the other 4 studies reported no significant differences. The common methodological limitations were unclear reporting about blinding of the outcome assessors and inadequate control of confounding factors. Conclusions: High-quality research is strongly recommended to determine the function of endogenous pain modulatory mechanisms in CLBP.