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

A study conducted by researchers at McGill University and scientists from Italy suggests that blocking inflammation after injury might make that pain chronic — a finding that challenges the standard approach to treating pain.

Chronic pain — especially in the lower back — is a common ailment, but scientists don’t know why some back injuries resolve themselves while others cause suffering for years.

In this study, researchers found that neutrophils, a type of white blood cell that helps the body fight infection and dominates the early stages of inflammation, play a key role in resolving pain.   

Jeffrey Mogil, researcher of the study and professor of psychology at McGill University, says standard medical practice for treatment of short lasting pain after injury might be the opposite of what we should be doing.

“We think that chronic pain develops because of inflammation so we think inflammation is bad and we should stop it. But what this study suggests is that yes, but at the cost of increasing your chances to develop chronic pain,” Mogil said.

While the findings have not yet been tested on humans in a clinical trial, several pain experts that are not affiliated with the study say it suggests a new way to look at how the body heals.

Testing 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 mice trials 

They examined the blood cells of 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. 

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

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

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

Researchers tested on mice and confirmed that blocking inflammation using drugs relieved them of pain short term, as judged by their sensitivity to touch. But the drugs prolonged the resolution of their pain — turning the acute pain into something more chronic.

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

Researchers found those taking anti-inflammatory drugs, like ibuprofen, naproxen, and diclofenac to treat their pain were much more likely to have pain two to 10 years later — a correlation that’s consistent with their other findings, but can’t determine what caused the ongoing pain.

By comparing blood samples between patients who had their pain resolved and those who didn’t, scientists found that people whose pain went away had experienced a lot of inflammation driven by neutrophils, a type of white blood cell. (Louis-Marie Philidor/CBC)

They also found those who took other painkillers, such as acetaminophen (Tylenol), were less likely to have chronic pain compared to those who took anti-inflammatory medication. 

Study should be taken seriously, says pain doctor

Dr. Hance Clarke, medical director of the pain research unit at Toronto General Hospital, says around 18 per cent of the population struggle with chronic back pain. 

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

“This is a pretty landmark finding,” he said in an interview with CBC News. 

“To find a molecular basis that relates to those who will go on to have a chronic pain problem versus those who are going to avoid that should be taken pretty seriously.”

Clarke says the mainstay treatment for a back injury should be heat, physiotherapy, stretching, massage and then potentially medication. 

“What these researchers showed was that, you know, we could trial other medications other than anti-inflammatory first potentially,” he said.

Dr. Hance Clarke, director of pain services at the 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 occur after injury. 

“We still need to really figure out at what point in time we should be intervening in that natural process, because it’s clearly shown that if you have a high number of these white cells … that you may actually do better in the long run,” he said. 

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

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

Clinical trial coming 

Clarke says around 90 per cent of people with an acute injury will find their pain goes away. 

Steven Katz, who lives in Toronto, is in the other 10 per cent; he’s been having pain in his lower back for years and an action as simple as picking up a pencil can cause a flare-up. 

Steve Katz suffers from chronic lower back pain. With this study’s findings, he says he might wait longer before reaching for anti-inflammatory medication during his next flare-up. (Mark Bochsler/CBC)

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

Katz sees his physiotherapist, Lauren Roberts, frequently for exercise and acupuncture. But on days when he can’t get out of bed, he reaches for medication like Robax and Advil. 

Now hearing about this study, Katz says he might wait longer before taking his painkiller medication. 

“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 not surprised by the study’s findings either — especially since similar discussions were taking place in the sports medicine field in 2015.

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

“There might be perhaps a negative side effect of taking NSAIDs [non-steroidal anti-inflammatory drugs], especially earlier in that inflammatory cycle that happens in the body. But people tend to not like to hear that, Roberts said. 

“That first 24 to 48 [hours], I would say if you can get through it, try and 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 pretty radical…. It overturns decades of standard practice and extraordinary claims require extraordinary evidence,” he said. 

“We used to care basically entirely about what produces pain and all the research was on that and now I think more people are realizing that maybe the better idea, is to try to figure out why pain goes away.”

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