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July 11 (UPI) -- While scientists have long noted a complex connection between a person's addiction to opiates, or "opioid use disorder," and chronic pain, the brain mechanisms linking the two have been poorly understood. Chronic pain may lead to the misuse of opiates, and people with chronic pain have a harder time quitting these addictive medications than people with opioid use disorder without such pain.
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So, scientists say, it's critical to determine how chronic pain and opioid use disorder relate to create better treatments.
Now comes what's being called a "first-of-its-kind study" by researchers at Ohio State University and the University of Michigan Medical School looking into one potential mechanism called "central sensitization" -- described as abnormal pain processing in the brain and spinal cord.
People with this "dysfunctional central nervous system pain modulation" tend to suffer more with pain because their spinal cords are "unusually good at sending pain signals" to the brain, and their brains struggle to turn off those signals once they arrive, causing heightened pain perception, researchers said.
The new research is the first to give patients with opioid use disorder a scale measuring central sensitization, said Dr. O. Trent Hall, lead author of the study. He is an assistant professor and an addiction medicine physician in Ohio State's Department of Psychiatry and Behavioral Health..
The study also provides the first evidence of central sensitization underlying the chronic pain/opioid use disorder relationship, and demonstrates a new tool for easily measuring this sensitization among individuals with the opiates problem, Hall said.
The findings were published Monday in PAIN Reports, an official journal of the International Association for the Study of Pain.
Researchers have been studying central sensitization -- this amplification of pain signals -- since the 1990s, but the pace of research has picked up since the 2010s, Hall told UPI in a phone interview.
In 2016, the International Association for the Study of Pain recognized central sensitization as its own mechanism, calling it nociplastic pain, he added.
While it is difficult to estimate the prevalence of this condition in the general population, Hall said, the study focused on a specific group -- people with chronic pain whom he described as "using opioids in a way that feels out of control to them and yet they continue using them compulsively even though they're aware it's harming them in some way."
Among individuals addicted to opioids, roughly 30% to 60% of them have chronic pain, he said. But, for unknown reasons, almost 90% of the study's sample had pain in one body region, "even though we didn't select people based on pain."
Not everybody with central sensitization has opioid use disorder, and not everybody addicted to opioids has the amplified pain syndrome, Hall said, "but when they co-occur, it may be a dangerous situation."
As a next step, Hall said he plans to study whether existing treatments for central sensitization -- including antidepressants and certain types of counseling and physical therapy -- may benefit patients with chronic pain and opioid abuse.
He suggests the University of Michigan's painguide.com as a good resource for people seeking information on handling chronic pain.
For the study, researchers administered the American College of Rheumatology 2011 Fibromyalgia Survey Criteria via electronic survey to measure the levels of central sensitization in 141 patients at Ohio State Wexner Medical Center's addiction treatment center in Columbus, Ohio.
Participants also answered questions about pain interference, quality of life, pain beliefs and their expectations for pain and addiction treatment.
Researchers measured quality of life in eight categories: general health, physical functioning, mental health, social functioning, vitality, bodily pain, role limitations due to physical health and role limitations due to emotional problems.
The bottom line? They found that having greater central sensitization was associated with worse quality of life -- "and pain interfering more in their daily lives" -- among patients addicted to opioids, Hall said.
Moreover, patients with higher levels of central sensitization were more likely to report pain as a major reason for the start of their opioid addiction and for putting off addiction treatment.
"This one mechanism of pain seems involved in the onset, maintenance, escalation and relapse of [opioid use disorder], and it's a major reason why people with OUD are not accessing treatment," Hall said.
"And that's why this [research] is important. We're trying to improve outcomes for people with OUD ... [and] by targeting this mechanism, we may be able" to do so.
Dr. Daniel J. Clauw, director of the University of Michigan's Chronic Pain and Fatigue Research Center, told UPI in a phone interview that "Of the people involved in this study, I come from the pain field and they come from the addiction field."
"I always thought that opioid use disorder with chronic pain in the background was something quite different from OUD without chronic pain, and this study suggests it may very well be ... and may drive different treatments," said Clauw, professor of anesthesiology, internal medicine/rheumatology and psychiatry at the University of Michigan.
"The bottom line is we think treating the underlying pain disorder in somebody [addicted to opioids] may be very helpful," and underlying chronic pain may be the reason they took opioids in the first place and the reason for relapse if the pain "hasn't been addressed front and center," Clauw said.
Currently, clinicians trying to handle patients' opioid abuse often just focus on addiction, Clauw said, explaining that he hopes the new study "causes more people to look at pain as a problem that must be co-addressed and co-managed."
In separate research, Hall and colleagues published a study in JAMA Pediatrics in January estimating that unintentional drug overdoses led to significant years of life lost for young Americans ages 10 to 24 between 2015 and 2019.
