Eficácia analgésica e mecanismos de ação da estimulação elétrica nervosa transcutânea: revisão sistemática e ensaio clínico randomizado

Abstract

Transcutaneous electrical nerve stimulation (TENS) is a non-invasive therapy that has been widely used for pathologies. However, this effect is correlated with opioid control and repeated stimulation of opioid receptors can lead to the development of analgesic tolerance with loss of therapeutic efficacy. The objective of study 1 was to carry out a systematic review to evaluate the action buttons induced by TENS with analgesic function in animals for a better understanding of their protocols and consequent results. Relevant articles were identified through a search of the following databases: PubMed, SCOPUS, Cochrane, Medline, Science Direct, Web of Science, CINAHL, Google Scholar, which was performed by two independent investigators through February 2021. Risk of bias included studies recording the RoB tool for animal intervention studies. To assess the quality of the study, the CAMARADES checklist was used. For meta-analyses with continuous results, we tested the effects of low- and high- frequency TENS compared to control groups, as well as low-frequency versus high-frequency TENS. A total of 6,984 titles were found and, after a thorough analysis, 53 studies were included for analysis. The results indicated that TENS has a substantial scientific basis for its hypoalgesic effect in preclinical studies. In addition, with the systematic analysis it was possible to assess the effectiveness, the limits of effectiveness, the need for further animal experiments and the design of any subsequent clinical trial, easing translational challenges. The aim of study 2 was to investigate whether repeated daily administration of TENS increasing intensity can delay analgesic tolerance in patients with chronic pain. This was a randomized, double-blind, placebo-controlled clinical trial that included 64 subjects with knee osteoarthritis allocated into two groups (active TENS or placebo TENS). High-frequency TENS treatment (100 Hz), 100 μs pulse duration at maximum sensory intensity tolerated was applied daily to the knee, five days a week, for four weeks, for 20 minutes. The intensity was increased with each session. Placebo stimulation (no stimulation) was of the same duration. The following were evaluated: pain intensity (11-point numeric scale), pressure pain threshold (LDP-algometry), motor performance (up and go test - TUG and multidimensional pain assessment (McGill Pain Questionnaire). of pain on each day of treatment when active TENS was used. However, it was necessary to increase the current intensity over time to maintain the effectiveness of TENS and reduce pain. In addition, the time required to complete the TUG test suffered significantly in the active TENS group compared to placebo TENS. These data suggest that repeated daily application of TENS decreases pain intensity in an intensity-increasing manner.