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.
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