The following is a summary of “Subgrouping of facilitatory or inhibitory conditioned pain modulation responses in patients with chronic knee pain. Explorative analysis from a multicentre trial,” published in the September 2023 issue of Pain by Larsen et al.
Conditioned pain modulation (CPM) responses are observed in healthy and chronic pain patients, but their clinical implications for phenotyping are unknown. Researchers performed a retrospective study to subgroup and compare chronic knee pain patients based on their CPM responses.
They conducted a cross-sectional study with 127 patients with chronic knee pain (due to osteoarthritis or after total knee arthroplasty). They categorized individual CPM responses into facilitatory (when test stimuli pain intensity increased with conditioning stimuli), inhibitory (when test stimuli pain intensity decreased), or no change (less than 5.3% change in pain intensity). Assessed clinical pain intensities, temporal summation, widespread pain, self-reported physical function, PainDETECT questionnaire, and Pain Quality Assessment Scale. The data were analyzed by comparing the inhibitory and facilitatory groups and using multivariate linear regression models.
The results showed that 54 patients exhibited facilitatory conditioned pain modulation (CPM) responses, 49 had inhibitory CPM responses, and 24 displayed no change in their CPM response. A notable difference emerged in self-reported physical function, with the facilitatory CPM group reporting better parts (54.4 vs. 46.0, P=0.028), and the same group also said more deep pain sensations (3.2 vs. 2.0, P=0.021). However, no differences were observed in the remaining outcomes. Furthermore, a correlation between higher clinical pain intensity and facilitated temporal summation was found in the facilitated CPM group but not in the inhibitory CPM group.
They concluded that clinical and experimental pain responses exist in chronic knee pain patients based on CPM responses.