Resolving Long-Standing Uncertainty about Whether Treatments Relieve Pain: The Example of TENS

In 1987, I started my PhD project to investigate the factors that influence the analgesic effects and clinical efficacy (effectiveness) of transcutaneous electrical nerve stimulation (TENS). At that time, the belief within health care was that TENS was a useful treatment to alleviate pain. In the 1990s the publication of systematic reviews of clinical studies evaluating the efficacy of TENS started to question the value of TENS for pain management. Uncertainty about the efficacy of TENS remains to this day, despite the publication of hundreds of randomized controlled trials (RCTs) spanning over 50 years. This week a comprehensive review was published in the journal Medicina where I critically evaluate how factors influencing the outcomes of RCTs have contributed to the ‘efficacy-impasse’ for TENS.

My review of the literature revealed a vast amount of research that has failed to answer, with any degree of certainty, the question of TENS efficacy. This is concerning, raising fundamental ethical issues about the publication of so much ‘inadequate research’ spanning over half a century.

“It is shameful that the vast amount of research spanning nearly half a century has failed to resolve the issue of TENS efficacy, resulting in longstanding uncertainty about whether TENS should be offered to patients in public health systems or covered by private healthcare insurance … “. p. 11

The situation is not unique to TENS, with long-standing unresolved debates about the efficacy of many pharmacological and non-pharmacological treatments used to manage pain.

I offered three approaches to resolve the efficacy-impasse for TENS:

1. To conduct a meta-analysis of all available RCT data, irrespective of type of pain, to strengthen statistical power and the level of certainty of the size of treatment effects from studies conducted to date. Our team has completed such a meta-analysis (the Meta-TENS study - submitted for publication).

2. To conduct RCTs that have over 200 participants receiving TENS and that use an enriched enrolment with randomized withdrawal design to enable optimisation of TENS treatment according to individual need. Our team has completed a preliminary study to evaluate the feasibility of such an approach (unpublished).

3. Perhaps controversially, I suggest that an answer about the efficacy of TENS will always be elusive because challenges of conducting and financing suitably robust RCTs on TENS are insurmountable. Thus, it may be prudent to abandon an approach that seeks to determine efficacy unless studies meet the criteria outlined in approach 2 (above).

In conclusion, I argue that patients continue to purchase and use TENS despite efficacy being elusive, so future endeavours may be better served focussing on how best to integrate TENS into existing pain management strategies. Such an approach may be appropriate to many other pain management techniques where uncertainty about efficacy remains elusive and longstanding.

Over 30 years have elapsed since I completed my PhD. During that time, I have observed an exponential rise in the quantity of research publications on the efficacy of TENS. My observations over that time are summarised in the final sentence of my review

“Perhaps clinicians, policy makers, funders and researchers need to reconsider the value of persisting with the production and publication of so many RCTs that fail to answer questions about efficacy.” p. 29.