Stimulated by Dimitrova et al 2019 & Zheng et al 2019.[1,2]
I first came across the acronym QST some years ago in one of the big national or international pain conferences where there are always numerous companies exhibiting extraordinarily expensive pieces of kit. QST devices appeared to be just another expensive bit of kit on wheels.
I was curious, but when I discovered that the majority of the thresholds tested were on skin, I soon lost interest. Very few of my patients have a primary complaint related to their skin, although a few of course have signs involving altered skin sensitivity.
Anyway, it took quite a while for QST to make it to the acupuncture party! Or should that be expressed the other way around? It probably should, but I’m sure I will be forgiven on this blog for being acucentric!
I guess it is the expense of the equipment that is the problem, so we have seen some papers coming out where it seems as though the research has been driven by the fact that the kit is available rather than being driven by the research question.
If you want to see all the prior papers, Petra Baeumler and colleagues published a very thorough review a few years ago including 85 studies where sensory testing was included. I mentioned this in a previous related blog – Temporal summation and acute acupuncture analgesia 2019.
The papers I am highlighting this week come from opposites sides of the globe – Portland, Oregon versus Melbourne, Victoria. They both involve sensory testing in healthy volunteers (n=28 vs n=26) before and after electroacupuncture (EA) – 100Hz vs 5/15Hz. Both papers are well reported and show some differences in sensory testing outcomes for us to consider.
The first, from the US, is from a team who in their day jobs perform ‘intraoperative neuromonitoring for awake craniotomies’ apparently, and therefore are keen to find ‘non-sedating analgesia that would provide pain relief while enabling the patient to participate in language and other cognitive intraoperative testing.’ I guess that explains the choice of high frequency EA, since they want immediate effects.
At this point I am desperately suppressing an image from Hannibal – the sequel to Silence of the Lambs.
Dimitrova and colleagues compared two groups that both had EA at moderate intensity to leg points. One group received bilateral EA at ST36—GB34 and ST41—LR3 – this was the ‘low dose’ group and targeted points in the vicinity of the peroneal nerves (superficial and deep). The ‘high dose’ group received bilateral EA at the same points plus two further pairs targeting the tibial nerve – SP6—KI9 and KI3—KI1. Well, EA to 8 points in the lower limbs is hardly low dose in my book, but EA to 16 points certainly would constitute a high dose and would require at least two standard EA devices.
They measured vibration detection threshold (VDT), cold detection threshold (CDT) and 3 different heat pain measures in both the right leg and the right hand. I have never quite understood why anyone is interested in VDT when assessing analgesic techniques, but hey, it is in the QST armamentarium, so why not just look? Well in this case it was lucky they did, since the results were different between the leg (local effect) and the hand (general effect). There were also some differences in the heat pain measures between the leg and hand, with greater changes in the leg.
Unfortunately, there were absolutely no differences between the two doses of acupuncture, so the differences I refer to above are effectively within-group differences of a cohort receiving EA. Still, the results are useful, and tend to indicate the power of local or regional effects over distant or generalised effects.
One other aspect I would like to highlight is the focus on large peripheral nerves in this paper and the assumption that these are being stimulated directly via EA. This is not at all likely to have happened since if a needle tip is close to a nerve bundle the large myelinated fibres with the lowest electrical threshold will be stimulated before any sensation from nerve endings is perceived. This will result in strong motor contraction or intense dermatomal paraesthesia long before the small fibres mediating acupuncture analgesia are affected.
So, now onto the second paper. This one, from the south of Australia, also used healthy subjects, but implemented a long-lasting hyperalgesia model using heat and topical capsaicin and more heat to test sensory changes after EA. The capsaicin was applied to the volar forearm (a popular target for this sort of thing) after it had been subjected to a heat application at 45oC for 5 minutes. This heat pain model was rekindled four times over the course of the experiment with a 5-minute application of heat at 40 oC. Don’t you love the term ‘rekindled’? I’m thinking of Hannibal again!
The outcomes were the area of mechanical hyperalgesia around the test site (a measure of central sensitisation), heat pain thresholds at the test site (a measure of peripheral sensitisation) plus a contralateral site, and the intensity of heat pain during the first minute of each rekindling.
The EA stimulation was as good as it could be. Muscle points in all four limbs and intensity high enough to get muscle twitch at 5/15Hz. The point combinations used were ST36—ST40 and LI10—LI4 bilaterally. The comparison group received non-penetrating sham EA, and the technique looked good – a guide tube tapped on the skin followed by the application of a bent needle preinserted into a standard plaster dressing.
The area of mechanical hyperalgesia reduced significantly in both groups, with no difference between real and sham EA. Similarly, there was no difference in heat pain thresholds. There was a significant difference in heat pain intensity ratings however, and this was in favour of the real EA. So, the authors did not find what they expected, but it was a good effort, and at least they came away with one clear difference over a sham technique that proved to be credible, thus adding to the accumulating psychophysical data supporting the idea that something real happens with acupuncture beyond the sometimes quite powerful context effects.
On that last note, I must mention a really nice review paper by my friend Frauke, with the striking title ‘Acupuncture for the Treatment of Pain – A Mega-Placebo?’, also out this week. Thank goodness for the question mark!
1 Dimitrova A, Colgan DD, Oken B. Local and Systemic Analgesic Effects of Nerve-Specific Acupuncture in Healthy Adults, Measured by Quantitative Sensory Testing. Pain Med Published Online First: 31 October 2019. doi:10.1093/pm/pnz276
2 Zheng Z, Bai L, O’Loughlan M, et al. Does Electroacupuncture Have Different Effects on Peripheral and Central Sensitization in Humans: A Randomized Controlled Study. Front Integr Neurosci 2019;13:61. doi:10.3389/fnint.2019.00061
3 Baeumler PI, Fleckenstein J, Takayama S, et al. Effects of acupuncture on sensory perception: a systematic review and meta-analysis. PLoS One 2014;9:e113731. doi:10.1371/journal.pone.0113731
4 Musial F. Acupuncture for the Treatment of Pain – A Mega-Placebo? Front Neurosci 2019;13. doi:10.3389/fnins.2019.01110