Neck Solutions

Treatment of chronic back pain by sensory discrimination training. A Phase I RCT of a novel device (FairMed) vs. TENS

From: BMC Musculoskelet Disord. 2008 Jun 28;9(1):97 [Epub ahead of print]

The causes of chronic low back pain remain obscure and effective treatment of symptoms remains elusive. A mechanism of relieving chronic pain based on the consequences of conflicting unpleasant sensory inputs to the central nervous system has been hypothesised. As a result a device was generated to deliver sensory discrimination training (FairMed), and this randomised controlled trial compared therapeutic effects with a comparable treatment modality, TENS.

60 patients with chronic low back pain were recruited from physiotherapy referrals to a single-blinded, randomised controlled, non-inferiority trial. They were randomised to receive either FairMed or TENS and asked to use the allocated device for 30 minutes, twice a day, for 3 weeks. The primary outcome variable measured at 0 and 3 weeks was pain intensity measured using a visual analogue scale averaged over 7 days. Secondary outcome measures were Oswestry Disability Index, 3 timed physical tests, 4 questionnaires assessing different aspects of emotional coping and a global measure of patient rating of change.

Baseline characteristics of the two groups were comparable. The primary outcome, change in pain intensity at 3 weeks showed a mean difference between groups of -0.1. The mean difference in change in ODI scores was 0.4. Differences in change of physical functioning showed that no significant difference in change of scores for any of these test. Changes in scores of aspects of emotional coping also demonstrated no significant difference in change scores between the groups.

FairMed was not inferior to TENS treatment. The findings have implications for further research on current chronic pain theories and treatments. Further work to explore these mechanisms is important to expand our understanding of chronic pain and the role of neuro-modulation.

Device treatment for pain has some obvious advantages over pharmaceutical treatments, particularly that nothing has to be ingested and the side effect profile is likely to be much less. It is also likely to be cheaper than pharmaceutical management and can be used in conjunction with those rehabilitation treatments for which there is evidence of efficacy. Device treatment is likely to have a potent placebo effect. There are many devices that purport to treat back pain. The current “market leader” is transcutaneous electrical nerve stimulation (TENS), estimated to be 1% of the analgesic market for back pain The treatment effect of TENS is attributed to influencing the “gate” proposed by Melzack and Wall in their Gate Control Theory of Pain. TENS has been commercially successful. However, the clinical benefits of TENS remain controversial and there is lack of consensus regarding its efficacy. Some studies suggest a lack of evidence to support its use in the treatment of chronic low back pain, while others found evidence of benefit, or have concluded that there is a lack of evidence of effect, rather than evidence of a lack of effect. The recent Cochrane Review concluded that there was limited or inconsistent evidence for TENS. However, no other device has any better evidence of efficacy and for this reason TENS was chosen as a comparator treatment for a new device (FairMed) that has been developed to deliver sensory discrimination training in patients with chronic back pain

The FairMed is a novel device and as such there are no existing data on effectiveness. It is difficult to establish what is a fair comparator to use in a trial with a new device. Whilst the Cochrane review of TENS concluded that there was limited evidence for TENS, there are no other devices that provide any better evidence of efficacy, nor any which have stood the test of time as well as TENS. For this reason TENS was chosen as a comparator treatment for a new device designed to help those patients with chronic back pain who continue to have serious difficulties, despite not being a treatment endorsed by current guidelines.

The findings of this trial demonstrate no significant difference in pain intensity reduction between the FairMed and TENS. This is in keeping with other trials investigating sensory changes, such as the findings of Guieu et al. and Lundeberg who also found no significant difference in pain reduction between vibratory stimulation and TENS in patients suffering with chronic musculoskeletal pain. Both trials used a control of a similar high frequency TENS and vibration protocol to the ones in the trial. There is a plethora of different outcome measures that can be used in the assessment of low back pain. In this study the physical outcome measures chosen were a walk test, timed stair climb and sit to stand. These physical tests have been advocated by other trial designs and reported for reliability in a similar clinical population to the one in this study, hence the rationale for their use. However, it is possible that selection of physical performance measures that stressed the spine more specifically, such as loaded forward reach may have been more responsive to change in this patient population.

The theory for the analgesic effect of TENS is suggested to be as a result of counter stimulation of the nervous system modifying the perception of pain. There is evidence to suggest that this same theory could be applied to the FairMed. Studies have demonstrated that superficial and deep mechanoreceptors exist with a high sensitivity to vibratory stimulation. With a surface area of almost 500cm2, the FairMed stimulates a large region of the lumbar spine and underlying tissues, indicating that pain alleviation could be attributed to the activation of these receptors. Functional magnetic resonance imaging (fMRI) of subjects has revealed reduced activity in the anterior cingulated, insula and thalamus; some of the key pain processing areas of the brain. There is evidence to suggest that the same is true for cognitively demanding distraction. Bantick et al reported decreased perception of painful stimuli in subjects receiving noxious thermal stimulus whilst engaged in a cognitively demanding task. Using fMRI, decreased activation in the same key components of the pain matrix have been reported. Although these results are based on acute experimentally induced pain, modulation of chronic pain could conceivably be achieved by the FairMed through interference from vibratory stimulation and cognitive regulation of attention. Furthermore, Flor et al demonstrated a reduction in phantom limb pain following a treatment programme using sensory discrimination training, demonstrated to be as a result of cortical reorganisation in the primary somatosensory cortex.