Chronic pain that persists after a traumatic event may be caused more by stress and other psychological factors rather than a lingering injury, according to a new study.
Researchers at the University of North Carolina School of Medicine say they’ve also identified a genetic risk factor for chronic pain after a stressful event such as a sexual assault or motor vehicle collision.
“Our study findings indicate that mechanisms influencing chronic pain development may be related to the stress response, rather than any specific injury caused by the traumatic event,” said Samuel McLean, MD, assistant professor of anesthesiology and senior author of the study published in the journal Pain.
“In other words, our results suggest that in some individuals something goes wrong with the body’s ‘fight or flight’ response or the body’s recovery from this response, and persistent pain results.”
The study assessed the role of the hypothalamic-pituitary adrenal (HPA) axis, a physiologic system that controls the body’s response to stressful events.
The study evaluated whether the HPA axis influences the severity of musculoskeletal pain six weeks after a car accident. Researchers found that a variation in the gene for the protein FKBP5, which plays an important role in regulating the HPA axis, was associated with a 20 percent higher risk of moderate to severe neck pain. The same genetic variant also predicted increased pain six weeks after a sexual assault.
“Right now, if someone comes to the emergency department after a car accident, we don’t have any interventions to prevent chronic pain from developing,” McLean said. “Similarly, if a woman comes to the emergency department after sexual assault, we have medications to prevent pregnancy or sexually transmitted disease, but no treatments to prevent chronic pain. This is because we understand what causes pregnancy or infection, but we have no idea what the biologic mechanisms are that cause chronic pain.”
“Chronic pain after these events is common and can cause great suffering, and there is an urgent need to understand what causes chronic pain so that we can start to develop interventions. This study is an important first step in developing this understanding.”
A researcher at Stanford University’s Division of Pain Medicine thinks the study findings could have wider applications to other types of chronic pain, including post-traumatic stress disorder (PTSD).
“People who acquire post-traumatic stress disorder following exposure to a traumatic stressor have major negative changes in thoughts, mood, and behavior. PTSD is associated with dyregulation of the HPA axis, and people with PTSD are at greatly increased risk for chronic pain, even if their initial trauma did not involve physical injury,” said Beth Darnall, PhD, Clinical Associate Professor, Stanford Systems Neuroscience and Pain Laboratory.
“While the current study did not examine people with a formal diagnosis of PTSD, the findings suggest that a genetic predisposition to HPA dysregulation plays a role in the persistence of pain following trauma. It will be very interesting for future studies to examine associations between childhood trauma and FKBP5, as well as whether FKBP5 more strongly predicts risk for fibromyalgia, a pain condition commonly associated with adrenal insufficiency.”