• D Carroll, R A Moore, H J McQuay, F Fairman, M Tramèr, and G Leijon.
• IPC 814, Pfizer Ltd, Sandwich, Kent, UK, CT13 9NJ. dawn.carroll@pfizer.com
• Cochrane Db Syst Rev. 2001 Jan 1(3):CD003222.

BackgroundTranscutaneous electrical nerve stimulation (TENS) is used in a variety of different clinical settings to treat a range of different acute and chronic pain conditions and has become popular with both patients and health professionals.ObjectivesTo evaluate the effectiveness of TENS in chronic pain.Search StrategyThe Cochrane Library, Embase, Medline, CINAHL and The Oxford Pain Database were searched. Reference lists from retrieved reports and reviews were examined. Date of the most recent search: March 1999.Selection CriteriaRCTs were eligible if they included the following treatment comparisons: active TENS versus sham TENS controls active TENS versus no treatment controls active TENS versus active TENS controls (for instance High Frequency TENS vs Low Frequency TENS) Studies of patients suffering chronic pain for three months or more which included subjective outcome measures for pain intensity, or pain relief were eligible for evaluation in this review. No restrictions were made to language or sample size. Data from abstracts, letters, or unpublished studies, and studies of TENS in angina, headache and migraine, and dysmenorrhoea were not included.Data Collection And AnalysisData were extracted and summarised on the following items: patients and details of pain condition, study treatments, study duration, design, methods, subjective pain outcome measures, methodological quality, results for pain outcome measures and adverse effects, and the conclusions made by the authors of the original studies. Extracted data and methodological quality of each report was confirmed by at least three of the reviewers.Main ResultsOf 107 reports identified from the searches, 88 were excluded as they did not fulfil the pre-defined entry criteria. Nineteen RCTs (from 18 reports) were evaluated. The included trials varied in terms of design, analgesic outcomes, chronic pain conditions, TENS treatments and overall methodological quality. Studies included single and multiple dose treatment comparisons of TENS. The studies were small. The reporting of the methods used and results for the analgesic outcomes were generally poor. TENS treatments and controls were often poorly defined. Few studies evaluated the long-term analgesic effectiveness of TENS and single dose evaluations of TENS are unhelpful in making clinical decisions of the long-term effectiveness of TENS in the management of chronic pain. Meta-analysis was not possible. Overall in 10 of 15 inactive control studies there was a positive analgesic outcome in favour of the active TENS treatments. For the multiple dose treatment comparison studies only three of seven were considered to be in favour of the active TENS treatments. For the active controlled studies, seven studies made direct comparisons between HFTENS and LFTENS. Five of seven studies could find no difference in terms of analgesic efficacy between HFTENS and LFTENS at any time point.Reviewer's ConclusionsThe results of this review are inconclusive; the published trials do not provide information on the stimulation parameters which are most likely to provide optimum pain relief, nor do they answer questions about long-term effectiveness. Large multi-centre randomised controlled trials of TENS in chronic pain are urgently needed.

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