Insights and actions, research review, radishes
Thanks for reading the fourth copy of my newsletter about radicular pain!
This month I was the interviewer on a new podcast episode about sciatica. I asked questions to Tina Price, whose writing I have referenced so often in my own. Tina has endless valuable inights into this subject and I strongly recommend you listen!
The podcast got me thinking about what we can learn from patients' experiences of radicular pain. I think there are some common themes that come up in qualitative literature and when you listen to patients speak. I set out to write about them for this newsletter. But, it ended up being too long for an email. So, I have put it on my website, here:
*** 7 insights from patients’ experiences of sciatica — and how to act on them ***
Which reminds me, I finally have a website. It was surprisingly difficult to design a site without loads of fancy boxes and colours and popups and banners, but I managed it!
Research review:
There have been a few really interesting and imaginative papers on the pathomechanisms of radicular pain recently. Here are three:
Defrin et al. looked in to what we mean by "shooting pain" and what might cause it. They found that while most clinicians imagine the "shooting pain" of sciatica to be a quick pain moving down the leg, some patients who describe shooting pain (or radiating pain) in fact mean a relatively slow movement (some people said as long as an hour!); some experience an "expansion" of pain rather than a movement; and, remarkably, some people feel shooting up the leg (!). Defrin et al. point out that it's weird that pain should shoot at all: when an afferent neuron is stimulated we feel it in one place. They float the hypothesis that the shooting felt by patients with sciatica is caused by a "travelling wave" of action potentials across the representation of the leg in the dorsal horn (akin to the homunculus in the brain).
This is such an enjoyable and satisfying explanation that it surely can't be true?
The second paper in our research review is the from labs of Dilley and Bove. If you are not familiar with Dilley and Bove's work, they have shown that when a nerve is inflamed the flow of axonal transport stops at that inflamed point and all the little ion channels get bunched up there instead of travelling to the end of the nerve. Where they are bunched up, they do what they do and start off action potentials. These areas of the axon with lots of transductive elements bunched up where they shouldn't be are called "abnormal impulse generating sites".
With Goodwin as the lead author, the team showed in their recent paper that these abnormal impulse generating sites are mechanically sensitive in proportion to the pressure exerted on them. They have a graded response just like normal nociceptors.
I think these two papers - by Defrin et al. and Goodwin et al. - can be joined together to suggest an explanation for the reports from Smyth and Wright that a gentle pressure on an irritated nerve root causes a proximal pain, and greater pressure causes pain to expand distally. As Goodwin et al. show, the harder the pressure on an irritated nerve, the greater the ectopic discharge. According to Defrin et al., a greater ectopic discharge will plausibly set off a greater "travelling wave" ‘down the leg’ of the body map on the dorsal horn. Whereas a light touch causing a lesser discharge will cause a lesser wave and only proximal pain. A fun theory.
Throwing a spanner in the works is our final interesting recent pathomechanisms paper by Jungen et al. They found that there is very little evidence that patients with sciatica have raised inflammatory biomarkers. The authors write candidly, "the results from this review are not overly convincing". They note that this sort of fits with what we see in real life - if inflammation was a big part of radicular pain, wouldn't NSAIDs and corticosteroid injections work much better than they do? Hmmm...
Bits and bobs
I found this pain management advice from a 1977 pamphlet. It struck me as so similar to today's advice but strangely alien in its tone...
I found some great images of pain by artists. They are all created for a "Mail-In Art Show." Here's one that shows sciatica:
Fact of the month: The word 'radicular' has the same origin as the word 'radish'. Both come from the Latin 'radix' which means ROOT.
David Poulter had a correction for my last newsletter on spinal anatomy. Basically, I got the definition of a spinal nerve wrong (I sort of got it tangled up in my mind as I was writing). Nerve roots are nerve roots until they join to become the spinal nerve. The portion that we call the spinal nerve is very short before it branches off again.
David also provided some additional images - see here, here and here.
If you haven’t seen it yet, here’s a fantastic patient-facing video on sciatica! Credit: Annina Schmi, Tina Price, Joel Fundaun and Laura Bassi.
Personal news!
I had my first peer-reviewed paper accepted! 🥳🥳 Yes, it's about radicular pain 😆 I'm too nervous to say more until it's actually in print.
Still no news about my green card as all immigration offices are closed til further notice 🌐. They did post me a work permit and a travel permit though which is great.
Spring arrived in Michigan much later than in England 🌱. While England was in bloom our trees were still bare. Once it arrived, it seemed to only last about three weeks until it felt like summer. But it was beautiful! So I’ll sign off with some photos.
Til next time,
Tom