Methodological quality in randomised controlled trials of transcutaneous electric nerve stimulation for pain: Low fidelity may explain negative findings

Abstract

The benefits of transcutaneous electrical nerve stimulation (TENS) for pain relief have not been reliably established, as most systematic reviews find poor methodological quality in many studies. The paradox within the evidence base for TENS is that despite identified sources of bias that may lead to an overestimation of treatment effects, no benefits for TENS can be clearly demonstrated. Conventional assessments of quality assume a single direction of bias, and little work has been undertaken examining other directions of bias. Our hypothesis was that low fidelity in studies (bias leading to an underestimation of treatment effects) may account for inconclusive findings. We included 38 studies from 3 recently published Cochrane systematic reviews that examined TENS for acute, chronic, and cancer pain. We extracted data relating to treatment allocation, application of TENS and to the assessment of outcomes. We quantified these data and judged this against standardised assessment criteria using a "traffic light" approach based on the number of studies reaching the standard. We identified significant sources of potential bias in both directions in relation to study design and implementation fidelity that have not been quantified previously. Suboptimal dosing of TENS and inappropriate outcome assessment were particularly prevalent weaknesses indicating low fidelity. We propose criteria for judging directions of bias in future studies of TENS that may be adapted to assess other trials in which implementation fidelity is important, such as other nonpharmacological interventions for pain. Poor implementation fidelity was identified as a significant source of bias in systematic reviews of TENS studies and might explain lack of consistent treatment effects of TENS in pain. Here, criteria for assessing methodology are proposed for use in designing future clinical trials of TENS.

Direct and Indirect Benefits Reported by Users of Transcutaneous Electrical Nerve Stimulation for Chronic Musculoskeletal Pain: Qualitative Exploration Using Patient Interviews

“…In addition to methodological issues such as ensuring adequate treatment, Bennett et al 3 identified adequate outcome assessment as a key issue which should be addressed to improve the quality of future research. Patient-reported outcome measures (PROMs) can be judged against a range of eight criteria 8 including reliability, validity and responsiveness.…”

Opioidergic effects of transcutaneous electrical nerve stimulation on pain and inflammatory edema in a rat model of ankle sprain

“…However, the mechanism involved in TENS analgesic effect is not completely understood 23 . In the present study, we extend these observations showing that a single session of LF-TENS or HF-TENS (10 or 100Hz) produced long-lasting reduction in mechanical inflammatory hyperalgesia and edema induced by ankle sprain in rat hind paw.…”

A Cochrane systematic review of acupuncture for cancer pain in adults

“…It has recently been suggested that low implementation fidelity (bias leading to an underestimation of treatment effects) might be present in studies using suboptimal doses of Transcutaneous Electrical Nerve Stimulation (TENS) and the same might be true of other non-pharmacological interventions such as acupuncture. Future studies should ensure adequate dosage and use appropriate outcome measures to avoid this problem 33. The design of future studies should also be adequately powered via the use of sample-size calculations, and investigators should consider the use of homogenous cancer populations.…”