Conditioned Pain Modulation and Temporal Summation of Pain in Patients With Traumatic and Non-Specific Neck Pain: A Systematic Review and Meta-Analysis.

In patients with neck pain, it is unclear whether pain inhibition and facilitation endogenous pain mechanisms are altered. This systematic review and meta-analysis aimed to improve their understanding by assessing conditioned pain modulation (CPM) and temporal summation of pain (TSP) in patients with neck pain associated with whiplash-associated disorders (WAD) or of a nonspecific neck pain (NSNP) nature compared to pain-free controls. Very low certainty evidence suggests: impaired CPM when assessed remotely in chronic WAD patients (n = 7, 230 patients and 204 controls, standardized mean differences (SMD) = -.47 [-.89 to -.04]; P = .04) but not locally (n = 6, 155 patients and 150 controls; SMD = -.34 [-.68 to .01]; P = .05), impaired CPM in chronic NSNP patients when assessed locally (n = 5, 223 patients and 162 controls; SMD = -.55 [-1.04 to -.06]; P = .04) but not remotely (n = 3, 72 patients and 66 controls; SMD = -.33 [-.92 to .25]; P = .13), TSP not facilitated in either chronic WAD (local TSP: n = 4, 90 patients and 87 controls; SMD = .68 [-.62 to 1.99]) (remote TSP: n = 8, 254 patients and 214 controls; SMD = .18 [-.12 to .48]) or chronic NSNP (local TSP: n = 2, 139 patients and 92 controls; SMD = .21 [-1.00 to 1.41]), (remote TSP: n = 3; 91 patients and 352 controls; SMD = .60 [-1.33 to 2.52]). The evidence is very uncertain whether CPM is impaired and TSP facilitated in patients with WAD and NSNP. PERSPECTIVE: This review and meta-analysis present the current evidence on CPM and TSP in patients with WAD and NSNP. Standardization of measurement methodology is needed to draw clear conclusions. Subsequently, future studies should investigate the clinical relevance of these measurements as prognostic variables or predictors of treatment success.

Conditioned pain modulation and psychological factors in young adults with recurrent or chronic neck pain.

BACKGROUND: Controversy exists with the presence of alterations in descending pain inhibition mechanisms in patients with non-specific neck pain (NSNP). The aim of the present study was to evaluate the status of conditioned pain modulation CPM, remote pressure pain thresholds (PPT), and psychological factors in a specific subgroup of patients with NSNP such as young adult students. In addition, possible associations between CPM, psychological factors, and pain characteristics were analyzed. METHODS: Thirty students with recurrent or chronic NSNP and 30 pain-free students were included in this cross-sectional study. The following measures were assessed: CPM, remote PPT, psychological factors (depression, anxiety, pain catastrophizing, and kinesiophobia), pain characteristics (duration, intensity, severity of chronic pain, interference with daily life), and central sensitization inventory (CSI). RESULTS: No significant differences were found in the efficacy of CPM between students with chronic or recurrent NSNP and pain-free students (ß coefficient = -0.67; 95% CI = -1.54, 0.20). However, students with pain showed a significantly higher remote PPT (mean difference = -1.94; 95% CI = -2.71, -1.18). and a greater presence of anxious (mean difference = 6; 95% CI = 2, 9) and depressive symptoms (mean difference = 8.57; 95% CI = 3.97, 13.16). In addition, significant moderate or strong correlations were found between CPM and pain intensity (partial r = 0.41), pain catastrophizing and mean pain intensity (r = 0.37), grade (r = 0.50), and interference of pain (r = 0.57), kinesiophobia and disability (r = 0.38), and depression and CSI (r = 0.39). CONCLUSIONS: Young adult students with chronic or recurrent NSNP present remote hyperalgesia and symptoms of depression and anxiety but not dysfunctional CPM.

Manual Therapy Effects on Nonspecific Neck Pain Are Not Mediated by Mechanisms Related to Conditioned Pain Modulation: A Randomized Clinical Trial.

BACKGROUND: Manual therapy (MT) is a treatment recommended by clinical practice guidelines in the management of patients with neck pain. However, the mechanisms through which MT works remain unknown. The aim of the present study is to investigate if MT is mediated by mechanisms related to conditioned pain modulation (CPM), comparing the effects of painful with a pain-free MT treatment. METHODS: A two-arm, parallel, randomized controlled clinical trial with concealed allocation and blinding of the outcome assessor was conducted in university students with chronic or recurrent nonspecific neck pain (NSNP). Participants received either a painful or pain-free MT session. Psychophysical variables including pressure pain thresholds, CPM, temporal summation of pain and cold pain intensity were assessed before and immediately after treatment. In addition, changes in neck pain intensity over the following 7 days and self-perceived improvement immediately and 7 days after treatment were assessed. RESULTS: No significant differences were found between groups in any of the psychophysical variables or in patients' self-perceived improvement. Only a significantly greater decrease in neck pain intensity immediately after treatment was found in the pain-free MT group compared to the painful MT group. CONCLUSION: The results suggest that the immediate and short-term effects of MT on NSNP are not mediated by CPM-related mechanisms.

Effects of Percutaneous and Transcutaneous Electrical Nerve Stimulation on Endogenous Pain Mechanisms in Patients with Musculoskeletal Pain: A Systematic Review and Meta-Analysis.

OBJECTIVES: The main aim was to determine the effects of percutaneous electrical nerve stimulation (PENS) and transcutaneous electrical nerve stimulation (TENS) on endogenous pain mechanisms in patients with musculoskeletal pain. DESIGN: A systematic review and meta-analysis. METHODS: The search was conducted on March 1, 2022, in the EMBASE, CINAHL, PubMed, PEDro, Cochrane Library, Web of Science, Medline, and SCOPUS databases. Randomized controlled trials comparing the use of transcutaneous or percutaneous electrostimulation with a placebo, control group, or standard treatment in patients with musculoskeletal pain were included. Outcome measurements were quantitative sensory testing somatosensory variables like pressure pain threshold (PPT), conditioned pain modulation, and temporal summation of pain. The pooled data were evaluated in Review Manager 5.4. RESULTS: Twenty-four randomized controlled trials (n = 24) were included in the qualitative analysis and 23 in the meta-analysis. The immediate effects of PENS and TENS on local PPTs were significant, with a moderate effect size (standardized mean difference [SMD] 0.53; 95% confidence interval [CI]: 0.34 to 0.72; P < 0.00001). When only studies with a lower risk of bias were analyzed, the heterogeneity decreased from I2 = 58% (P < 0.00001) to I2 = 15% (P = 0.01), and a decrease in the overall effect was observed (SMD 0.33; 95% CI: 0.7 to 0.58). The short-term effects on local PPTs were not significant when compared with the control group (P = 0.13). The mid-term effects on local PPTs were significant, showing a large effect size (SMD 0.55; 95% CI: 0.9 to 1.00; P = 0.02). The immediate effects on conditioned pain modulation were significant, with a large effect size (SMD 0.94; 95% CI: 0.48 to 1.41; P < 0.0001). CONCLUSION: PENS and TENS have a mild-moderate immediate effect on local mechanical hyperalgesia in patients with musculoskeletal pain. It appears that these effects are not sustained over time. Analyses suggest an effect on central pain mechanisms producing a moderate increase in remote PPT, an increase in conditioned pain modulation, but further studies are needed to draw clearer conclusions.