BACKGROUND: This review aimed to examine existing systematic reviews regarding the clinical efficacy of transcutaneous electrical nerve stimulation (TENS) in reducing pain in patients with chronic pain conditions. METHODS: Data concerning the methods and conclusions of the reviews and individual trials were extracted. The data from the individual trials were subcategorised according to the validity of outcome measures, methodological quality, sample size, and 'dose response' (if any) of TENS. RESULTS: Two of the six reviews concerning TENS and chronic pain reported that high intensity TENS applications were more effective compared to placebo than low intensity applications. However, the reviews and the authors' conclusions were based on a total of eight high quality trials which reported positive findings on a visual analogue scale or numeric rating scale which measured pain relief/intensity. DISCUSSION: Data from chronic pain trials that use these outcome measures show that any dose-related responses of TENS cannot be conclusively demonstrated as a result of the number of confounding variables (eg, inadequate design, low statistical power and the many differences in TENS protocols such as repeated versus single treatments). CONCLUSION: To address these issues, recommendations are made for future systematic reviews and randomised controlled trials. Such recommendations include the need for more comprehensive and rigorous tools in assessing substantive trials within systematic reviews.

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