BACKGROUND: Previous studies have found a negative association between a conditioned pain modulation (CPM) response and pain catastrophizing among pain-free individuals. This study investigated the difference in CPM response between individuals with chronic low back pain (CLBP) and pain-free controls, and the association between pain catastrophizing and CPM response.
METHODS: In all, 22 individuals with CLBP and 22 sex-matched and age-matched controls underwent a CPM protocol. Pressure pain thresholds (PPTs) were measured on the lower leg and lower back. The CPM response was registered as the change in PPT from baseline to after a cold pressor test (CPT). Catastrophizing was assessed using the Pain Catastrophizing Scale before the CPM protocol in both groups.
RESULTS: Analysis of variance showed no interactions in PPT between groups and test sites at baseline or post-CPT. PPT increased significantly after CPT in the control group (P<0.006) but not in the CLBP group. The results showed significantly less pain inhibition participants with among participants with CLBP compared with controls (P<0.04). The CPM response was negatively associated with Pain Catastrophizing Scale scores in the CLBP group (rs=-0.67, P=0.0006) while no association was found in the control group.
DISCUSSION: This study demonstrated a reduced CPM response and a negative association between pain inhibition and pain catastrophizing in individuals with CLBP. The results suggest that catastrophizing thoughts are associated with the efficiency of descending endogenous pain modulation in CLBP, although a causal relationship cannot be inferred.