What’s happening in the brains of people with chronic pain and addiction?

As a physician with a background in both chronic pain and addiction, O. Trent Hall, DO, has cared for many patients suffering deeply with both conditions, and he realizes that treatment options are limited.

Chronic pain may lead to opioid use disorder (OUD), and people with chronic pain and OUD have a harder time quitting opioids than people with OUD alone. So it’s critical, he says, to find answers to how pain and OUD are connected in the brain.

That’s why Dr. Hall led a team of researchers at The Ohio State University Wexner Medical Center and College of Medicine and the University of Michigan Medical School in a first-of-its-kind study that explored one potential mechanism — central sensitization — in people with opioid use disorder.

The journal PAIN Reports, an official journal of the International Association for the Study of Pain, published the findings of the study.

Central sensitization refers to abnormal pain processing in the brain and spinal cord. People with central sensitization have spinal cords that are unusually good at sending pain signals to the brain, and brains that struggle to turn off those signals once they arrive. This means people with greater central sensitization tend to suffer more with pain than others.

Scientists have long noticed a connection between OUD and chronic pain, but brain mechanisms linking OUD and chronic pain are poorly understood, says Dr. Hall, who provides addiction treatment to patients at Ohio State’s East Hospital and Talbot Hall and is a clinical professor of Addiction Medicine in the Department of Psychiatry and Behavioral Health in the Ohio State College of Medicine.

“It’s important to me to search for new ways to help,” he says. “But we can’t create better treatments for chronic pain and opioid use disorder without first understanding how the two relate. I did this study because I believed it might offer a new window into what is happening in the brains of patients needing help with pain and addiction.”

For the study, researchers recruited 141 people from the Ohio State Wexner Medical Center’s Talbot Hall addiction treatment center. Study participants responded via electronic survey to questions on the American College of Rheumatology 2011 Fibromyalgia Survey Criteria, along with separate questions about pain interference and quality of life. They also shared their beliefs about pain and their expectations of pain and addiction treatment.

“Our study is the first to give patients with OUD a scale that measures central sensitization,” Dr. Hall says. “It provides the first evidence of central sensitization underlying the chronic pain and OUD relationship and demonstrates a new tool for easily measuring central sensitization among individuals with OUD.”

Researchers measured quality of life across eight life domains including general health, physical functioning, mental health, social functioning, vitality, bodily pain, role limitations due to physical health and role limitations due to emotional problems. Dr. Hall says they weren’t surprised to find that greater central sensitization was associated with worse quality of life among patients with OUD.

“Additionally, patients higher in central sensitization were more likely to report pain as a major reason for why their opioid addiction first began, as well as for putting off addiction treatment, continuing and increasing their use of opioids, and fear of pain causing OUD relapse in the future,” says senior author Daniel J. Clauw, MD, director of the Chronic Pain and Fatigue Research Center at the University of Michigan.

By suggesting that central sensitization may be an important underlying factor complicating the treatment of chronic pain and OUD, the study provides an example for other clinicians and researchers to measure central sensitization in OUD, which could help them produce better treatments for people suffering with the two conditions.

Next, Dr. Hall plans to follow patients with central sensitization and OUD over time to find out if they respond differently to treatments or have different outcomes. He also plans to study whether existing treatments for central sensitization are beneficial for patients with chronic pain and OUD.