Canadian study offers important clue as to why some back pain becomes chronic

A study by McGill University researchers and Italian scientists suggests that blocking inflammation after injury could make this pain chronic, a finding that challenges the standard approach to pain treatment.

Chronic pain – especially in the lower back – is a common condition, but scientists aren’t sure why some back injuries resolve on their own while others cause years of suffering.

In this study, researchers found that neutrophils, a type of white blood cells that help the body fight infections and dominate the early stages of inflammation, play a key role in pain resolution.

Study researcher Jeffrey Mogil, a professor of psychology at McGill University, says standard medical practice for treating short-term pain after injury might be the opposite of what we should be doing.

“We think chronic pain develops because of inflammation, so we think inflammation is bad and we should stop it. But what this study suggests is yes, but at the cost of ‘increase your chances of developing chronic pain,’ Mogil said.

Although the results have yet to be tested on humans in a clinical trial, several pain experts not affiliated with the study say it suggests a new way of looking at how the body heals. .

Test blood cells and mice

The study, which was published in Science Translational Medicine last Wednesday, was conducted by nearly two dozen researchers who examined pain in three phases, using human blood cells and tests in mice

They looked at blood cells from 98 patients with acute low back pain and looked for markers of inflammation. Three months later, they did the same test – comparing those who still had persistent pain and those who didn’t.

Patients whose pain was gone showed more inflammation on the first visit, which seemed to be caused by neutrophils, a type of white blood cell. On the second visit, their blood cells showed a change in gene expression of several thousand genes.

Jeffrey Mogil, a neuroscientist and professor of psychology at McGill University, says the findings challenge what has become the standard treatment for short-term pain. (McGill University)

“People who haven’t resolved their pain, absolutely nothing has happened to their blood,” said Dr. Luda Diatchenko, another study researcher and professor of dentistry and medicine at the University. McGill. Both groups of patients used anti-inflammatory drugs, she said.

The researchers tested on mice and confirmed that blocking inflammation with drugs relieved them of pain in the short term, judging by their sensitivity to touch. But the drugs prolonged the resolution of their pain, turning the acute pain into something more chronic.

In the final phase of the study, they looked at data from 500,000 people from the United Kingdom Biobank, a database of medical information obtained from half a million volunteers.

The researchers found that those who took anti-inflammatories, such as ibuprofen, naproxen and diclofenac to treat their pain were much more likely to have pain two to 10 years later – a correlation that is consistent with their other findings, but cannot determine what caused the continued pain.

By comparing blood samples between patients whose pain resolved and those who did not, scientists found that people whose pain resolved experienced a lot of inflammation caused by neutrophils, a type of white blood cell. (Louis-Marie Philidor/CBC)

They also found that those taking other pain relievers, such as acetaminophen (Tylenol), were less likely to experience chronic pain than those taking anti-inflammatory medications.

Study should be taken seriously, says pain doctor

Dr. Hance Clarke, medical director of the Pain Research Unit at Toronto General Hospital, says about 18% of the population suffers from chronic back pain.

Even without randomized clinical trials, Clarke said there are implications for understanding what happens differently between acute pain and chronic pain.

“It’s a pretty historic discovery,” he said in an interview with CBC News.

“Finding a molecular basis that relates who will continue to have a chronic pain problem versus who will avoid it is something to be taken very seriously.”

Clarke says the basic treatment for a back injury should be heat, physical therapy, stretching, massage and possibly medication.

“What these researchers have shown is that, you know, we could test other drugs other than anti-inflammatories first,” he said.

Dr. Hance Clarke, director of pain services at Toronto General Hospital, says the study has findings that should be taken seriously when it comes to chronic pain. (Dr. Hance Clarke)

Clarke says there’s a natural immune response that needs to happen after an injury.

“We still really have to figure out when we should be intervening in this natural process, because there’s been clear evidence that if you have a high number of these white blood cells…you can actually do better in the long run,” he said.

But until the results are tested in human trials, Clarke still advises patients who can’t get out of bed due to pain to take an anti-inflammatory drug to help them function again. .

“We don’t want the message to be…you should be in unbearable pain for an extended period of time because that’s the natural process,” he said.

Upcoming clinical trial

Clarke says about 90% of people with an acute injury will have their pain go away.

Steven Katz, who lives in Toronto, is among the remaining 10%; he has had lower back pain for years and something as simple as picking up a pencil can cause a flare up.

Steve Katz suffers from chronic lower back pain. With the results of this study, he says he could wait longer before taking anti-inflammatory drugs for his next flare-up. (Mark Bochsler/CBC)

“It’s kind of like a shooting pain and it gets to the point where I can’t really walk anymore,” he said.

Katz frequently sees her physical therapist, Lauren Roberts, for exercise and acupuncture. But on the days he can’t get out of bed, he takes drugs like Robax and Advil.

Now that he hears about the study, Katz says he might wait longer before taking his painkillers.

“I’m not surprised… At the same time, I’m allergic to pain,” he said. “It depends on the level of pain, frankly.”

Roberts, who founded the Running Physio clinic in Toronto, says she’s also not surprised by the study’s results, especially since similar discussions have taken place in the field of sports medicine. in 2015.

Physiotherapist Lauren Roberts, who founded the Running Physio clinic in Toronto, says the field of sports medicine has also discussed the positive role inflammation can play in healing. (Mark Bochsler/CBC)

“There could be a negative side effect of taking NSAIDs [non-steroidal anti-inflammatory drugs], especially at the beginning of this inflammatory cycle that occurs in the body. But people tend not to like hearing that, Roberts said.

“That first 24 to 48 [hours]I would say if you can pull it off, try to see if you can.”

Mogil says the team is preparing to confirm their work through randomized controlled trials with humans.

“What we’re saying here is quite radical… It overturns decades of common practice and extraordinary claims require extraordinary evidence,” he said.

“We used to basically worry about what was causing the pain and all the research was on that and now I think more and more people are realizing that maybe the best idea is to try to figure it out why the pain disappears.”