It’s not enough just to feel – it’s about ‘what do you feel?’


 

Pain. 2007 Dec 1

Tactile discrimination, but not tactile stimulation alone, reduces chronic limb pain.

Moseley GL, Zalucki NM, Wiech K

This interesting study by the prolific Lorimer Moseley suggests that it’s not good enough for people with complex regional pain syndrome to just be exposed to tactile stimuli, but they need to do something with that stimulus for it to translate into changes in pain intensity and ability to discriminate.
This study was a four phase (A–B–C–D) within subjects repeated measures design. The first phase was a no-treatment waiting period. The second phase was the stimulation only condition. The third phase was the discrimination condition. The duration of each of these phases was between 11 and 17 days (randomly allocated for each participant). The fourth phase was a three-month follow-up period.
The stimulation only condition involved On a digital photograph of the affected limb, five points were marked Two cork probes (2 and 11 mm in diameter, respectively) were mounted atop a spring-loaded cartridge such that the pressure with which each probe could be applied to the skin was standardised.A screen was positioned to prevent the subject from seeing the affected area. Stimulation involved applying one of the probes to one of the marked points. The type of probe and the marked point were randomised using a random numbers table. Interstimulus interval was 15 s. Three 6-min blocks of 24 stimuli were undertaken with a 3-min rest period between blocks. Thus, each treatment session involved 72 stimuli and lasted 24 min, and was repeated every week day.
The discrimination phased was exactly the same, however, participants were given a photograph of their limb on which the stimulation points were marked. They were also shown the two probes. During the tactile stimulation, participants responded to each stimulus by stating (i) the location of the stimulus (i.e. the corresponding number on the photograph) and (ii) the type of probe.
The effect of tactile stimulation and discrimination on function (task-specific NRS)Tasks selected by each participant reflected the body part that was affected. For example, most participants selected sleeping; most participants with CRPS of the upper limb selected ‘dressing’, ‘eating’ and ‘driving’; participants with CRPS of the dominant upper limb selected ‘writing’ or ‘using my hand’; all participants with CRPS of the lower limb selected ‘walking’ and ‘wearing a shoe’.At baseline, means ± SD function score was 2.2 ± 0.8. Function changed over the course of the study (main effect of time; (F(4, 48) = 70.05, p < 0.001). Pairwise comparisons revealed that there was no change in function during the stimulation phase [mean (95% CI) = 3.1 (2.0–4.1)], nor during the waiting period [2.5 (1.9–3.2); p > 0.34 for both)]. Function was higher at post-discrimination [5.5 mm (34–38 mm)] than it was at post-stimulation, post-waiting period or at baseline (p < 0.001 for all). The mean (95% CI) effect size for the function score was 1.9 (1.1–2.8). Function had not changed further at follow-up [5.5 (4.5–6.5), p = 0.98], but it was still higher than it was at post-stimulation, post-waiting period or at baseline (p < 0.001 for all)

Unfortunately, this study was conducted with a group of only 13 people with complex regional pain syndrome, so we don’t know whether it is readily generalisable, but it does provide some food for thought for both occupational therapists and physiotherapists. Both occupational therapists and physiotherapists would argue that goal-directed activities that are relevant to the individual are much more likely to engage the interest and hence ‘motivate’ people to carry them out more readily than ‘exercises’. The challenge has been to identify suitable activities – and to establish why this type of activity should be provided as opposed to the more easily developed ‘exercises’. Now here is a clinical study demonstrating that yes, outcomes can be maximised by engaging the person in active involvement in the activity.

What I really liked about this study was the use of real functional tasks as the ‘ultimate’ measure of whether the intervention worked. Of course it would be great to see a truly randomised study in which an alternative and perhaps competing treatment such as graded exposure is used – I wonder whether by providing an ‘interesting’ activity there is reduction of anxiety and hence more likelihood that the person will use their affected limb. If a really interesting and engaging activity is used in a graded hierarchy, it may prove even more successful. An additional measure to use in this case would be one assessing fear or anxiety about pain, or even one assessing acceptance.

PMID: 18054437 [PubMed – as supplied by publisher]

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5 comments

  1. I love Lorimers work!
    That guy is an absolut genius.
    This study reminds of one done by Merzenich where they showed that simply stimulating the fingers didn’t change cortical maps in monkeys – the change only took place when the monkeys were given a task.

    It’s the small details provided by studies like these that make a huge difference when treating patients.

  2. Thanks for that comment Matthias. I agree that he’s been doing some interesting work – but as a scientist I want to wait until there have been some further studies in different populations and by different researchers before drawing strong conclusions from these experimental findings to the kinds of clinical populations that I work with.

  3. I agree.
    Most of his studies are done with only a few patients at a time.
    It seems to me that he is “just” trying to confirm a hunch. 😉
    That way he can move forward much faster than anyone else.

  4. Yup, I though as much – and because of that we can’t really make generalisations to many clinical populations. A shame because we need to do so – or use single subject research designs…

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