Strong EA & CPM in OAK

Stimulated by Lv et al 2019.[1]

My eldest two cherubs demonstrating examination of the knee 😉
One is now an actor – guess which one!

The paper that I am highlighting in this piece has two relatively novel features. First, and most interesting is the testing of two different doses of active EA (electroacupuncture) in a relatively large sham-controlled clinical trial on OAK (osteoarthritis of the knee), and the second is the use of CPM (conditioned pain modulation) as an outcome measure in a clinical trial as opposed to an observed measure in different patient groups.

CPM is a measure for the efficiency of descending pain modulation – notably deficient in fibromyalgia, and some other patients with chronic pain.[2] It is measured using the change in rating of a test stimulus before and after adding a noxious conditioning stimulus. In this case the test stimulus was prodding a tender point on the patient’s painful knee 3 to 5 times within a 1cm diameter with a 180g von Frey filament. Maximilian (Max) Ruppert Franz von Frey (1852–1932) was an Austrian-German physiologist who was born in Salzburg. He is most well-known for developing a series of filaments of different diameters (originally different grades of animal hairs) used to apply graded pressure stimuli. The 180g version is number 19 out of 20 – the second thickest.

The conditioning stimulus generally involves immersion of a foot or hand in uncomfortably hot or cold water. In this case it was the contralateral hand in cold (10-12oC) water for 1 minute. The percentage reduction in average subjective pain rating on VAS from before to after a minute of cold-water immersion was recorded as the outcome.

The primary outcomes were VAS pain, CPM value and WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index).

EA was applied in 30-minute sessions 10 times over 2 weeks at a 2Hz continuous frequency. Four points were used unilaterally – EX-LE-5—ST35 (the ‘eyes of the knee’), SP10—ST34. Patients were randomised to either strong EA, weak EA or sham EA in a 2:1:1 ratio. Strong EA involved 0.32x40mm Hwato needles inserted 25-40mm and manipulated to generate needling sensation followed by 30 minutes of EA at the maximum tolerated intensity from 2 to 5mA. The weak EA group had the same needling and EA at 0.1 to 0.5mA until the point of first perception of current. The sham EA group were needled with 0.2x25mm needles in ‘non-points’ about 2cm away from the locations in the true EA groups to a depth of 5 to 10mm. No attempt was made to generate typical needling sensation, and EA was applied as in the weak EA group.

So from a WMA perspective we have moderately strong EA to deep somatic tissue compared with minimal EA to deep somatic tissue and minimal EA to superficial tissues. At least they are all different! Or we might even ignore the minimal EA and say EA vs MA (manual acupuncture) vs superficial needling.

Obviously I am a bit irritated by the unnecessary penetration of the knee joint! As I must have said many times, from a physiological standpoint there is no logic in needling a space with few nerves and the potential albeit small of causing the devastating condition of septic arthritis.

The results showed both EA and MA to be better than superficial (p<0.01) for all outcome measures apart from CPM at week 1 (after 5 daily sessions). The most interesting result; however, is that EA was superior to MA for CPM at week 2 (after 10 sessions). It was also superior in the VAS pain outcomes at both week 1 and 2.

At risk of confusing you with acronyms, CPM is also known as HNCS (heterotopic noxious conditioning stimulation)[3] and originally as DNIC (diffuse noxious inhibitory controls).[4,5]

In my early days of acupuncture, I often heard clinicians and researchers in the pain world dismissing acupuncture as a form of DNIC.[6] I complained to my senior colleagues at the time that it didn’t make sense to me since acupuncture was mostly not noxious, and rather than being performed at the other end of the body (heterotopically) it was mostly performed close to the problem area. But both acupuncture or EA to deep somatic tissue and CPM may have a common pathway via the PAG (periaqueductal grey), raphe nuclei in the medulla and the descending inhibitory tracts. In order to be generated via superficial (skin) nerves it must be noxious and perhaps far away, but when generated via deep somatic tissue the necessary stimulation of high threshold nerves is not usually accompanied by the perception of noxious sensations.

So what this paper seems to show is that between 6 and 10 sessions of proper EA reduces pain from OAK and that this is associated with an enhancement in the functioning of the descending inhibitory pathways as measured by CPM.

I wonder if there is any chance it might be recommended by NICE in near future?[7]


1         Lv Z, Shen L, Zhu B, et al. Effects of intensity of electroacupuncture on chronic pain in patients with knee osteoarthritis: a randomized controlled trial. Arthritis Res Ther 2019;21:120. doi:10.1186/s13075-019-1899-6

2         Yarnitsky D. Conditioned pain modulation (the diffuse noxious inhibitory control-like effect): its relevance for acute and chronic pain states. Curr Opin Anaesthesiol 2010;23:611–5. doi:10.1097/ACO.0b013e32833c348b

3         Sprenger C, Bingel U, Büchel C. Treating pain with pain: supraspinal mechanisms of endogenous analgesia elicited by heterotopic noxious conditioning stimulation. Pain 2011;152:428–39. doi:10.1016/j.pain.2010.11.018

4         Le Bars D, Dickenson  a H, Besson JM. Diffuse noxious inhibitory controls (DNIC). I. Effects on dorsal horn convergent neurones in the rat. Pain 1979;6:283–304.

5         Le Bars D, Dickenson AH, Besson JM. Diffuse noxious inhibitory controls (DNIC). II. Lack of effect on non-convergent neurones, supraspinal involvement and theoretical implications. Pain 1979;6:305–27.

6         Le Bars D. Pain modulation triggered by high-intensity stimulation: implication for acupuncture analgesia? Int Congr Ser 2002;1238:11–29. doi:10.1016/S0531-5131(02)00412-0

7         Cummings M. NICE, electroacupuncture, and osteoarthritis. Int Musculoskelet Med 2014;36:47–9. doi:10.1179/1753614614Z.00000000068

Declaration of interests MC