Scientists have long tried to understand what causes an individual’s response to injury or disease to evolve from acute pain, which is an immediate response to a hurt, to chronic pain that continues for months or years after apparent recovery. Several recent studies suggest that chronic pain may come to reside not so much in brain areas connected to the original site of the injury or disease, but more broadly in areas of the brain associated with a complex mixture of other influences.
“The research suggests that chronic pain differs from acute pain in that it affects cognitive and emotional circuitry rather than just sensory circuitry,” says David Borsook, MD, PhD, Director of the P.A.I.N. Group at MGH. “Chronic pain is a fire in the brain that affects mood and cognition and makes the enjoyment of the rewards of life more difficult.”
This concept is illustrated by a large study of 4,300 adults ages 50 and older, in which scientists attempted to identify the factors linked to increased risk for chronic, widespread pain. The researchers asked study participants to fill in questionnaires with information about their pain levels, mental health, physical health, lifestyle, and other factors. About 2,700 study participants reported having some pain at the outset of the study, but none reported widespread pain.
However, after three years, 25 percent of participants who had reported some pain, and another eight percent of participants who had reported no pain had developed widespread pain. The factors most significantly linked to increased risk for chronic widespread pain was non-restorative sleep, anxiety, memory impairment, and quality of life, according to a paper published online Feb. 13, 2014 in the journal Arthritis & Rheumatology.
“The study suggests that changes in body chemistry, anatomy, and function associated with the initial injury or disease have redesigned the brain’s circuit boards and put normal emotional processing into disarray,” says Dr. Borsook. “The person no longer reacts normally.”
WHAT YOU CAN DO
See your doctor and follow treatment recommendations, Dr. Borsook advises. Then try the following strategies for easing chronic pain:
- Get regular exercise. With your doctor’s okay, try to work out moderately at least 30 minutes a day, five days a week.
- Ensure healthful sleep. Take care to practice good sleep hygiene, with regular sleep times, a comfortable, quiet, and darkened sleep environment, and relaxing, low-key activities prior to bedtime. Avoid excessive caffeine and alcohol consumption, and refrain from heavy meals and exercise immediately before retiring.
- Participate in life. Socializing, learning new skills, helping others, and participating in hobbies are examples of rewarding and mentally challenging activities that can help take your mind off your pain.
A number of new hypotheses about the causes of chronic pain focus on its emotional dimensions. In addition to the study discussed above, the latest theories in this category suggest that:
Chronic pain is tied to a shift in areas of brain activity. Researchers compared brain scans of pain-related brain activity in participants with short-term back pain with participants with long-term back pain. They found that pain activity was centered in brain regions involved in acute pain in the participants with short-term pain, but was centered in areas of the brain thought to mediate emotion in those with long-term pain.
Short-term pain patients were followed for a year, during which time those whose pain persisted were observed to have experienced a shift in brain activity from brain areas involved with acute pain to brain areas involved in emotion. “The results demonstrate that brain representation for …back pain can undergo large-scale shifts in brain activity with the transition to chronic pain,” the researchers concluded in a paper published in the September 2013 issue of Brain.
Chronic pain may involve abnormal stress responses. Research in the March 2013 issue of Brain suggests that a recurrent stressor such as chronic back pain may lead to maladaptive physiological responses to pain. Compared to study participants without back pain, participants with chronic back pain who were subjected to a pain stimulus were found to have higher levels of the stress hormone cortisol, smaller volume of a brain region called the hippocampus (involved in emotions, learning, and short-term memory), and greater activity in a related brain area involved in anticipatory anxiety and associative learning.
Additional research that has found evidence of impairment of neuroplasticity (the brain’s ability to learn by responding structurally and functionally to new information) in chronic pain patients, a development that may make recovering from chronic pain more difficult.
Other studies suggest that chronic pain may involve changes in connectivity between brain areas involved in mood and cognitive function. This finding offers a possible explanation for why chronic pain patients move beyond symptoms of sensory pain to develop brain changes that result in anxiety disorders, problems with decision-making, and other issues.
“In a way, chronic pain can be likened to an epoxy adhesive,” explains Dr. Borsook. “Initially, the pain may be tractable and responsive to treatment, but once it has ‘set’ by making changes to brain circuits, it may become harder to deal with. Of course, the development of chronic pain is affected by environmental, genetic, psychological, and other issues as well, along with the individual personality characteristics of each patient.
“Individuals may be able to ease their symptoms on their own by making positive changes in three important domains—their sleep quality, their exercise levels, and their engagement in socialization and other pleasurable activities that can provide distraction and help ward off depression.” (See What You Can Do.)
A number of new drugs under development show promise for the treatment of some types of chronic pain, Dr. Borsook says: “Pharmaceutical trials involving certain specific medications for migraine, neuropathic pain, and arthritis have been very promising, and may help us get away from current medications with psychological overtones, such as opioids. We need more of these highly effective, non-opioid drugs that ideally have few, if any, side effects.”
Aside from pharmacotherapies, researchers are studying a variety of potentially promising technologies for chronic pain, including vagus nerve stimulation (sending regular mild electrical pulses through the skin or from an implanted device to the vagus nerve for the purpose of interfering with pain signals), and transcranial magnetic stimulation (a non-invasive technique using a device that generates a magnetic field outside the head to alter pain circuits inside the brain) Other research suggests that cognitive behavioral therapy (talk therapy), mindfulness meditation, and acupuncture may also be helpful in reducing chronic pain.
“High-quality-outcomes research is badly needed to confirm the efficacy of these treatments compared to placebo before they are widely used in clinical settings,” Dr. Borsook says.