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Science round-up: six painful science stories from 2023

 •  • 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 PainScience.com: a library of major articles and books about common painful problems and popular treatments. See the blog archives or updates for the whole site.

To kick off 2024, here’s six intriguing 2023 studies I never got around to sharing last year …

  • A knee “injury” that was actually a disease
  • High rates of complications from surgical repair of “slipped” disks
  • Aging is … infectious? Fascinating basic science paper showing the surprising role of (retro) viruses in aging
  • Why does pain often last long after healing should be done? We may finally know!
  • Explaining obesity without reduced activity levels
  • Cyst got your tongue? Maybe your neck and head too? A weird cause of head and neck pain

A knee “injury” that was actually a disease

Ferreira et al tell the frustrating story of a hockey referee who went through several months of therapy and investigation of a “presumed knee injury” … but it was all barking up the wrong tree. The real explanation of the pain? The early stages of Parkinson’s disease. Physical therapists and surgeons all missed it. Not judging. Diagnosis is hard! Medicine is messy! (Okay, maybe judging a teensy bit.)

Although dystonia is often more obvious, it can be subtle and readily mistaken for ordinary musculoskeletal problems. And it’s always important to bear in mind that stubborn painful problems can be early warning signs of more serious diseases… and although any one type may be rare, they are common as a group. I added this case study to my overview of many possible causes of pain.

High rates of complications from surgical repair of “slipped” disks

Schepens et al. reported on poor outcomes from thousands of Dutch lumbar disk herniation surgeries, with straightforward and ugly results: almost a quarter (23%) had “one or more undesirable outcomes,” with many people getting a second surgery, nerve blocks, and/or opioids to cope after their failed treatment.

That’s really a lot of poor outcomes. In fact, I think you'd be hard-pressed to find a common elective surgery with worse stats.

I explore disk herniation in detail in my low back pain book — and there are a whole bunch of substantial updates on that topic coming early in 2024. This citation will definitely be included.

Aging is … infectious? Fascinating basic science paper showing the surprising role of (retro) viruses in aging

Endogenous retroviruses (ERVs) are the remnants of ancient viral infections: virus parts integrated into our DNA and passed down through generations. Most are harmless, and many play a role in normal genetics and physiology. But some are probably not harmless. Liu et al. is a highly technical study that showed something new and kind of amazing about aging: that the “resurrection” of endogenous retroviruses is “a biomarker and driver for aging.” Specifically, “the accumulation of HERVK retrovirus-like particles (RVLPs) mediates the aging-promoting effects in recipient cells.” They showed this by suppressing the effect in vivo, which points towards possible anti-aging therapies. Exciting stuff.

Pain and aging are forever entangled (see “inflammaging”), so I’m always interested in aging science. For a thorough dorky discussion of this paper (but they do try to be comprehensible), see the This Week In Virology episode, “Aging Is Infectious.”

Why does pain often last long after healing should be done? We may finally know!

Willemen et al. supplied a possible answer: “mitochondrial and metabolic disturbances in sensory neurons,” basically. Clear as mud? Let’s translate that:

Sometimes, after an injury or illness, pain is amazingly persistent even long after the initial problem seems to be healed. The study showed that a temporary bout of inflammation can permanently “damage” sensory neurons, change them in a bad way, making them making them more sensitive for the long haul, specifically due to a change in their “batteries” (mitochondria). Tweaking these mitochondrial changes — either by slowing down their activity, messing with a specific protein’s expression, or adding in a missing metabolite — can prevent that long-lasting sensitization. Which also proved that mitochondrial dysfunction was the problem in the first place. Very cool.

Alas, they did this in rats, not people. Still, this is some great basic pain science. I have spent most of my career wondering why twenty-year-old ankle sprains can still throb and twinge, and this may well be the explanation. Good to know!

Explaining obesity without reduced activity levels

People are burning fewer calories these days, but probably not for the reason everyone assumes: that is, not because we move less. Speakman et al. — and many others, there are dozens of authors — did an extremely complex analysis to show that people definitely have reduced energy expenditure, but they traced that to reduced basal metabolic rates, and not declining physical activity. Weird, right?

Something has changed in our physiology! For instance, “one of many possible explanations” is eating more saturated fats. And what happens when you burn fewer calories? You end up wearing them. “This study therefore identifies a novel potential contributor to the obesity epidemic.”

And unhealthy people have more pain. (Not that obesity is always unhealthy, but it often is.)

Cyst got your tongue? Maybe your neck and head too? A weird cause of head and neck pain

Mourad et al. gives us another case study involving a very tough diagnosis … but this time one that was made quickly despite the challenges.

A 75-year-old man had pain in his neck and the back of his skull. “Although difficult to observe” because of face masks, his speech was unclear and he was salivating excessively (and the word of the day for me is “sialorrhea”). Those were the clues that led to diagnosis of hypoglossal nerve palsy, caused by a rare spinal cyst. The tongue is controlled by the hypoglossal nerve (one of twelve big cranial nerves that emerge from the base of the brain, covering an incredible variety of neurological jobs). This kind of palsy is extremely rare and mostly interferes with the tongue, but — fascinating to me as a pain guy — it can also just cause neck and head pain.

What a great example of a weird cause of a very common symptom. And again: individual rare things are rare, but there are so many of them in medicine that they are collectively common. The head and neck is a real hot spot for oddities like this, which makes troubleshooting headaches particularly challenging.