Why would sciatica take a fortnight to kick in? Pt 1.
Sympathy for the Meakins. Is it because of a disc?
Thanks for reading the 35th edition of my sciatica newsletter. This newsletter tracks my research as I write a book about lumbar radicular pain!
Unfortunately Substack doesn’t allow me to send really long emails. So I’ve split this piece into three and the other two installments will be sent out tomorrow and the day after.
“Every ‘simple’ backache has the potential to be a nerve root problem” - Louis Gifford
Five years ago I was deadlifting and, on the fifth rep, I felt something go. Well, I felt it going on the fourth rep, but I thought 'what the heck' and did the fifth rep anyway, and that's when it went.
I felt back pain pretty much straight away. My back slowly seized up over the next few hours. I spent the next few days with hot packs or ice packs on it, not sleeping very well. This kind of thing had happened to me two or three times before, and I expected that this time like those times it would be sore for a few weeks and then go back to normal.
And in fact, after a month or two, that is pretty much what happened with the pain in my back. What was different this time was that a couple of weeks after my deadlifting incident, another pain joined the party: over the course of a few days, a nagging, unusual, prickly sensation crept down the back of my leg and settled in my calf, where it stayed for the next few months. The pain was not nice but, thankfully, not that bad either. Flexion eased it, and extension made it worse.
After a couple of months of this leg pain, I went to see a physio (I was a physio student at the time). I ended up seeing Rob Tyer; it was the first time we had met, and now we're working on a clinical book together, but that's another story.
According to Rob's letter to the GP, which I still have a copy of, I had "a grossly diminished left ankle jerk reflex, with associated altered sensation in the foot but not lower leg." And my "left sided toe standing demonstrate[d] reduced plantarflexion power and early fatigue compared to the left."
Partly because of some other things in my medical history, Rob suggested I get an MRI. I did, and it looked like this:
Thankfully, with time, my calf pain went away and my nerve function returned. Who knows whether that herniation is still sitting there; I reckon probably not.
I was reminded of all this recently because Adam Meakins seems to be going through something that is in some ways similar. As I understand it, here's what's happened to Adam (I'm discussing his case with permission!). While deadlifting, he felt something bad happen in his back (I think, like me, he even felt a twinge on one rep but did the next one anyway). He got back pain immediately, which like mine was is also better with flexion and worse with extension. And, according to his tweets and a message he sent me, his back pain has now been joined by leg pain, weakness and numbness. Unlike my leg symptoms, Adam's leg pain and numbness are on the front of his leg, and the worst of his weakness is in his knee. But like my symptoms, it took about two weeks after his deadlifting injury to kick in.
As far as I can tell, although it's almost never discussed in the literature, a delay of a few days or even a couple of weeks is a not too unusual as a pattern of onset for painful radiculopathy. And that's going to be the focus of this post. Why is there sometimes this delay?
Before we go ahead, one quick comment on the epistemic status of this post: it's on the specultive side. These are hypotheses based on the literature; they are interesting to think about, they maybe help some clinicians to interpret some clinical situations, and maybe at the best they're also illuminating to some patients who are wondering what is going on in their bodies. But I don't really know the answer to this question, it's all very speculative!
Ok, let's get started. Let's look at it through a few different lenses, starting with the disc side of things.
Is a disc the culprit?
Disc herniations cause radicular pain and radiculopathy through a combination of mechanical pressure (they prod, pin, twist and squash nerve roots) and chemical irritation (the stuff inside discs seems to be pro-inflammatory and might also start off an auto-immune reaction).
Typically we think of disc herniations as sudden events that are over in a short time: the nucleus sort of splurges or, erm, ejaculates out and then it sits there and causes trouble.
In fact, disc herniations sometimes seem to be more slowly-evolving events, that can even go through stages. Adams and Hutton, following their observations in cadavers, coined the term 'gradual disc prolapse' in 1985. They wrote that "a prolapse may occur over days and months".
If so, it would be plausible that a disc could herniate to a certain point and cause back pain, and then progressively herniate a bit more, eventually reach the nerve root and cause radicular pain.
A study by Seo and colleagues confirms this process in real life. The authors observed patients with painful disc herniation over the course of six months, and found that one third of patients' herniations got gradually bigger over time. They also found that of all the patients who had contained disc herniations - meaning restrained by the posterior longitudinal ligament - 20% of them developed uncontained herniations during the study period.
So maybe a gradually-progressing disc herniation explains mine and Adam's late-onset radicular pain?
The problem is, Seo and colleagues didn't find any meaningful correlation between changes in disc size and worsening of patients' symptoms. Of the patients whose pain got worse over the study period, some had disc herniations that were getting smaller and some had herniations that were getting bigger. And this does fit with a broader literature that shows a weak association between herniation size and pain. On the other hand, Seo and colleagues' study is small, and took quite infrequent measurements, so the chance of their missing a real effect is quite high.
Maybe we can learn a bit more by looking at studies that really get at the difference between back pain and leg pain, which is after all what the mystery is here: why did the leg pain come on later? There are two studies here that shed some light (thanks to David Poulter for pointing them out to me). Pople and Griffith, and Reihani-Kermani both found a really remarkable association between leg pain without back pain and disc extrusions (see here if you are new to terms like disc extrusion, protrusion etc; the short version is, extrusions are big and protrusions are small.)
In the study by Pople and Griffith, 96% of people with leg pain but no back pain had a disc extrusion; in the study by Reihani-Kermani, people with radicular pain alone were 6.5 times more likely to have an extrusion, and if their radicular pain increased as their back pain decreased they were fully 10x more likely. Although these are just two studies, the size of the differences between groups is very unusual! They don't directly answer our question, but they suggest that with delayed-onset radicular pain, if the waxing of radicular pain is accompanied by a waning of back pain (which is what happened for me, I'm not sure about Adam), then an extrusion is the likely culprit (which it was for me).
Does this mean the extrusion has developed gradually, causing back pain at first then, as it gets bigger, radicular pain? There is no way to tell. It could be that it developed suddenly and compressed the nerve root from day one, i.e. from 'the deadlift incident', but the radicular pain was delayed for other reasons (of which more later!)
All in all, it seems to me that a gradually-developing disc herniation is a plausible explanation for late-onset radicular pain, notwithstanding that weak association between herniation size and clinical symptoms. And, it seems like if the late-onset radicular pain coincides with an easing off of the back pain, and you had to bet on it, then you'd put your money on an extrusion being the culprit, although who knows whether it was sudden or gradual. I’ll also put in a quick word for a ‘migrating’ disc herniation: one that detaches and moves around after it has herniated. Although I haven’t mentioned it above, that too could explain late-onset radicular pain.
Let's shift our focus to the nerve side of things, where there may be some more answers.
Do changes in the nerve explain the delay?
It's fairly normal for nerve problems to have a delayed, sometimes very delayed onset. There are many examples. Nerve avulsion injuries can be painless until, a few days or weeks later, they definitely aren't. Apparently, for a sizable minority of amputees, it takes longer than a year for phantom limb pain to develop. Some people undergoing chemotherapy find the worst of the chemo-induced nerve pain comes weeks or months after their final dose, a phenomenon known as coasting. And nerve injuries in neonates can be painless until the child reaches puberty!
So maybe it is not just the disc. Let's look at the effects of mechanical pressure and chemical irritation on nerve roots, to see if we find a delay…
End of part 1! Part two coming tomorrow.
EDIT: Part 2 HERE
A quick note
This is the first post I’ve managed in a good few weeks. I’ve been a bit distracted with work, with a trip home to England (my first in two years!) and with moving to a bigger apartment (the baby is due in one month now!)
But also I’ve been hesitant to post because this newsletter has quite a lot of subscribers now, which is great, but has left me kind of stuck about what it is for and what I’m supposed to write in it. At first when the subscribers were mostly people I more or less knew, I didn’t feel too hesitant to send out scrappy emails that were actually newsletters: things I’d been up to and things I’d read. As the newsletter has got more subscribers, I’ve felt more hesitant to send that kind of email and more obliged to craft my posts properly and make them less personal. On reflection, I think this I should ignore this hesitancy and try as much as possible to post regular, ‘scrappy’ emails about what I’m up to and what’s on my mind. (I guess this particular email was somewhere in the middle - it took a lot of work to draft and redraft, but the content itself is a bit more ‘thinking out loud’.) So, until life gets in the way again, these newsletters should be getting more regular (and a maybe a bit more scrappy).
Til next time,