YOUR HEALTH Magazine by UHN Krembil Brain Institute

Understanding chronic pain

UHN scientists & physicians are finding new ways to treat a condition you can’t see

Lara Pingue, pictured here with her husband and two children, was a runner and practiced yoga when she suffered a herniated disc in her lower back in 2018. The injury took months to be diagnosed, and her acute pain gradually transformed into chronic pain.
Pingue tried everything from physiotherapy to medication to steroid injections to surgery, but nothing eliminated the pain entirely. "When the pain was at its worst, it was like a screeching, loud alarm bell going off," she explains. "Now it's like a hum, but the sound is always there. That's how I describe living with chronic pain."

Everyone has felt acute pain, but for more than eight million Canadians, chronic unrelenting pain is part of everyday life.

"It's an invisible disability," says Dr. Andrea Furlan, a senior scientist at UHN's KITE Research Institute and a physiatrist with UHN's Toronto Rehabilitation Institute, about what's known as chronic pain. "I've had patients tell me they wish they had an amputation, cancer or a scar so people would take them seriously."

"The International Association for the Study of Pain agrees that anything beyond three months should be considered chronic pain," notes Dr. Anuj Bhatia, Director of the Comprehensive Integrated Pain Program at UHN and a clinician investigator with the Krembil Brain Institute.

Chronic pain often comes on after a surgery or injury, or is part of a condition. Most people experience pain during the first six weeks after an injury, with those feelings subsiding within the next six weeks. Sometimes, though, the pain doesn't disappear.

Dr. Furlan compares the body's pain system to a home fire alarm. There may have been a reason to set off the alarm, but when it continues to blare, even after the smoke has cleared, something is clearly wrong with the system itself – that's chronic pain. "Now you have to call the alarm company to fix the system," she says. "Myself and Dr. Bhatia, we are the doctors of the alarm system."

How chronic pain works in the body

Dr. Anuj Bhatia likens the body's pain circuitry to an upside-down tree.

Think of a pain signal as follows: A drop of water lands on a leaf (initial pain), which is absorbed by the leaf, flows into the branches, through the trunk and into the roots. When the first set of neurons carrying your pain signal reaches the trunk – your spinal cord – it reacts by sending pain-dampening signals back to the source of your pain. A second set of neurons carries the pain signal from your spinal cord to the brain, and a third set of neurons in the brain processes that pain.

Searching for answers

Drs. Bhatia and Furlan are both actively researching the way the brain processes pain and how chronic pain differs from acute pain. Using functional magnetic resonance imaging (fMRI) – a live look at how blood flows through the brain – scientists have gained a better understanding of the change that takes place between acute and chronic pain.

With acute pain, the area of the brain associated with the body part that hurts lights up on an fMRI. When someone begins experiencing chronic pain, that same area lights up, but so do peripheral areas in the brain associated with emotions like anxiety and depression.

"Pain is not just a sensory, biological phenomenon that is coming from the tissue that is damaged or diseased," notes Dr. Furlan. "It is a combination of many factors. But all pain is real."

Dr. Bhatia has been working with neuroscientists at UHN to demonstrate how patients' brains light up differently before and after pain treatments, depending on what medication is used. The patterns are as unique as each person, but Dr. Bhatia and his team have identified certain patterns that predict how well a patient will respond to a particular treatment, or if they'll respond at all.

That type of predictive ability is the 'holy grail' in the pain scientific community, he says. "The right medicine for the right patient at the right time – that is really the target. So, we are making some progress. Are we there yet? No, but we will get there."