By Pat Anson, Editor

A new study by UK researchers raises an intriguing question: Does chronic pain change brain chemistry and make pain more tolerable?

The answer is yes, according to a small study at the University of Manchester. Researchers there used Positron Emission Tomography imaging (PET scans) to measure the spread of opioid receptors in the brains of 17 arthritis sufferers and nine healthy control subjects

When they applied heat to the skin of study participants to induce pain, researchers found that the more opioid receptors they had, the higher their ability was to withstand pain. The number of opioid receptors was highest in arthritis sufferers, suggesting their brain chemistry had changed in response to chronic pain.

"As far as we are aware, this is the first time that these changes have been associated with increased resilience to pain and shown to be adaptive,” said Dr. Christopher Brown. "Although the mechanisms of these adaptive changes are unknown, if we can understand how we can enhance them, we may find ways of naturally increasing resilience to pain without the side effects associated with many pain killing drugs."

It’s been known for a long time that we have receptors in our brains that respond to natural endogenous opioids such as endorphins. Those same receptors also respond to opioid pain medications.

Some people seem to cope better with pain than others, and knowing more about their resilience and coping mechanisms may lead to the development of new ways of treating pain.

"This is very exciting because it changes the way we think about chronic pain,” said Anthony Jones, a professor and director of the Manchester Pain Consortium. "There is generally a rather negative and fatalistic view of chronic pain. This study shows that although the group as a whole are more physiologically vulnerable, the whole pain system is very flexible and that individuals can adaptively upregulate their resilience to pain.

"It may be that some simple interventions can further enhance this natural process, and designing smart molecules or simple non-drug interventions to do a similar thing is potentially attractive."

Researchers at Stanford University in California have also been studying this subject, trying to learn why some chronic pain sufferers are more resilient to pain.

“I think this study emphasizes some very important points about pain resilience,” said Dr. Drew Sturgeon, a fellow in the Stanford University Pain Management Center and Stanford Systems Neuroscience and Pain Laboratory. “If you think about chronic pain as something that poses a constant challenge and requires frequent adaptation, it makes sense that we would see changes in the brain that correspond with this process.  We see it frequently from a psychological standpoint, where people are able to learn and develop better strategies for coping with pain and reduce their fear and negative thoughts about pain after dealing with it for a while.”

Sturgeon and his colleagues say resilience may also stem from an enhanced ability to enjoy the rewarding parts of life – which makes it easier to cope with pain.  

“The idea would be that if a person had more opioid receptors available they would be more sensitive to the good stuff in life, and therefore more motivated by pleasurable experiences, such as spending time with friends, exercising -- rewards that get us back on the road to living a meaningful life,” said Beth Darnall, PhD, a pain psychologist, clinical associate professor at Stanford University and author of Less Pain, Fewer Pills.

“Theoretically, people who are known to be resilient probably have more endogenous opioids -- or they have made choices in life to optimize their experience of endogenous opioids and therefore have honed an internal reward system.”

Whatever the cause of resilience, many patients hope further studies will uncover new ways of treating pain.

"As a patient who suffers chronic pain from osteoarthritis, I am extremely interested in this research. I feel I have developed coping mechanisms to deal with my pain over the years, yet still have to take opioid medication to relieve my symptoms,” said Val Derbyshire. “The notion of enhancing the natural opiates in the brain, such as endorphins, as a response to pain, seems to me to be infinitely preferable to long term medication with opiate drugs.”

The University of Manchester study is being published in Pain, the official journal of the International Association of the Study of Pain.