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No obvious neck abnormalities in headache patients

 •  • by Paul Ingraham
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Weekly nuggets of pain science news and insight, usually 100-300 words, with the occasional longer post. The blog is the “director’s commentary” on the core content of a library of major articles and books about common painful problems and popular treatments. See the blog archives or updates for the whole site.

Do some headaches come from the neck? It seems obvious that they do, doesn’t it? To at least half the people who’ve ever had a headache.

But now a study seems to say otherwise, reviving a decades-old debate about how headaches work. In today’s post, I explore the significance of this vexing new data. Is it a surprise? Is this the end for Team Cervicogenic Headache? What will happen? *munches popcorn*

The new study showed no sign of vertebral or intervertebral disc abnormalities in the necks of headache patients, which appears to be at odds with a widely and firmly held belief that some headaches are actually driven by neck pain — “cervicogenic” headache.

In my own headache book, I more or less declare for Team Cervicogenic. But my opinion is loosely held, and I will gladly follow the science and the experts wherever they lead me over time. This study could be an important new direction.

“A comparative shape analysis of the cervical spine between individuals with cervicogenic headaches and asymptomatic controls”
Masharawi et al. Scientific Reports. Volume 11, Number 1, 19413. Sep 2021.

The paper is quite readable, for a scientific paper, and you can get the whole thing. I enjoyed it, which is unusual. Scientific papers vary greatly in the quality of both the writing and the science they are about. A scientific paper is a written report on something actually done by scientists, and all too often what they did was ill-conceived and poorly executed, and/or the writing is pretentious and tortuous. This paper, fortunately, is a clearly written account of a useful experiment.

But nothing’s perfect, and even a perfect study would still only lock-in a single piece of the puzzle of pain.

The authors’ mostly normal neck bones, as revealed by a CT scan. A CT scan is like a deluxe X-ray — like an X-ray, it mainly shows bones, but it has the three-dimensionality of magnetic resonance imaging.

That’s a lot of neck measuring

Masharawi et al took CT scans of 80 people aged 20-40, and measured many specific features of their cervical spines, thousands of measurements in all — nineteen thousand of them. Someone sure stared at a lot of spreadsheets.

Forty of the subjects were headache free.

The other forty not only had headaches, but headaches that were dead-ringers for “cervicogenic” headaches. Their aching heads all strongly fit a clinical description of a cervicogenic headache. And better still: that diagnosis was “confirmed” in every case by relieving their pain, profoundly but temporarily, with an anesthetic injection in the neck. Such nerve blocks are widely regarded as strong evidence that headaches can indeed be caused by neck issues. (It’s not quite the slam dunk it seems to be, but it certainly is an important clue.)

This ideal subject selection is a great strength of this study, making its results far more useful than they would have been otherwise (and no doubt a logistical nightmare). These people had headaches that seemed about as cervicogenic as a headache can possibly seem. If the condition of the spine has anything to do with headaches, you might well expect to see some differences in these patients.

The utterly negative results

No differences were found. Diddly and squat. Bup and kis.

Not one statistically significant variation in any measurement. Average values for all measurements were more or less identical, as if the study subjects were all clones. The graphs in the paper tell the story effectively.

The obvious interpretation is that the condition of the spine has nothing to do with headaches. If it had anything to do with it, even a little, there would be at least a modest sign of it here. This interpretation strongly confirms a bias against cervicogenic headache, and it was fun to watch some experts pounce on this and declare victory… prematurely.

The obvious interpretation isn’t the only interpretation. This is science! Uncertainty reigns supreme, and this study cannot “settle” anything. It’s valuable data in a legit, ongoing debate, but it's not the coup de grace for cervicogenic headaches.

There are two major limitations of this study, both clearly acknowledged by the authors…

Limitation one: bone shape versus everything else

The first and worst limitation is that Masharawi et al studied only bone shape and relative position. Hard tissue, not soft. (With one important exception: much can be learned about intervertebral discs from images of vertebrae.)

We already know from many other sources that the structure of the spine correlates only loosely with chronic pain. This is a notorious truth in this field. It is not just possible, it’s standard for people to have apparently spinal pain without any detectable spinal abnormality, even using technology that can detect soft-tissue issues (MRI). Broadly speaking this is because (a) there are so many possible abnormalities that they are simply hard to find, and (b) there are many other biological and neurological factors that determine whether or not we hurt, with or without a visible issue in the tissue.

And that’s why, as a card-carrying member of Team Cervicogenic Headache, I would have predicted this result. I never believed in the first place that there would be a visible link between headache and signs of arthritic degeneration.

Especially in younger people.

Limitation two: Twentysomethings and thirtysomethings

Masharawi et al also studied just forty relatively young people, aged 20–40, averaging almost exactly 30. It’s not a major limitation, because they chose their subjects so carefully — these weren’t just any forty youngish people with headaches, but forty youngish people with exactly the kind of headache that could be explained by visible abnormalities of the spine.

But it’s a still a weakness. Perspective: there are more types and causes of headache than there are people in this study.

A similar study with more and older subjects might well have had different results. For instance, it is plausible that tissue insult begins years before there is any detectable effect on the visible condition of bones — and yet even then it might correlate only loosely with it, because there are so many other factors involved.

Given all the variables, your pain-free group will almost certainly be polluted with folks who have some neck abnormalities, and vice versa — and yet, on average, the ones with abnormalities are might still be somewhat more likely to have pain. You could easily still miss that signal in two hundred people in their forties. You might need to look at five hundred people in their fifties.

We actually have low back pain data that tells a story just like this. Brinjikji et al studied a much larger number of older subjects — arguably the better approach — finding that pain correlates poorly with spinal structure, but also that it does correlate. It seems highly plausible that the neck works similarly.

I am shocked — shocked, I say — that younger people with headaches have normal necks!

I think it’s terrific that we have this data, and it’s a useful and clear piece of the puzzle. But, as good as it is, it is a bit quelle surprise, and not remotely a deal-breaker for the hypothesis that some headaches are probably from in the neck, driven by cervical nociception (tissue insult detection), and that phenomenon should be expected to correlate poorly with vertebral condition, especially in younger people.

There are plenty of ways that necks could still hurt — and heads with them — without showing up on 40 CT scans, no matter how painstakingly measured.

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My headache book has now been updated with a citation to Masharawi et al. The headache book was also recently updated with the tongue-tied topic — just the two most recent of about a dozen noteworthy updates over the last couple years.