To answer this question, Dr. Carragee analyzed the psychological evaluations of his patients. He soon discovered that a person’s emotional state—and not the anatomical state of his back—was the best predictor of back pain. As Dr. Carragee notes, “The structural problems were really overwhelmed by the psychosocial factors. Almost without exception, people without any of these mental or social risk factors were able to deal with their backache. But people with a psychological problem had a much tougher time doing that. For them, the pain was often crippling and catastrophic.”
While scientists have yet to find the specific mechanisms that connect psychological problems to chronic pain, they are uncovering some clues. One possibility is that mental disorders make people more vulnerable by weakening the brain regions and neurotransmitter systems that are involved in the perception of chronic pain. For example, a brain-imaging study published last August by researchers at the University of Wisconsin at Madison found that people with clinical depression were much less able to regulate their negative emotions. According to Tom Johnstone, PhD, who led the research, when depressed individuals tried to turn off their emotions, these attempts backfired. The more effort they put in, the more activation there was in the emotional areas of the brain. As a result, bad feelings tended to spiral out of control.
A similar process might be at work in chronic pain. According to this hypothesis, pain persists in the emotional areas of the brain because patients are unable to turn it off. Whenever they think about the pain, they just make it worse. The Wisconsin researchers speculate that depressed individuals might have a “broken link” in the brain, which makes the regulation of negative emotion impossible. What makes this research valuable is that it opens up new possibilities for treating chronic pain. In recent years, for example, doctors have found that antidepressants, especially tricyclics, are often effective treatments for chronic back pain. These drugs help control the emotions that the patients cannot.
Stress is another risk factor for chronic pain. One back surgeon, who wished to remain anonymous for fear of offending his patients, says he has seen several men develop back pain shortly after becoming engaged. “Weddings are stressors,” he says, “and that stress can exacerbate the experience of pain.” Intriguing clues are beginning to emerge as to how stress might modulate pain. Joyce DeLeo, PhD, a neuroscientist at Dartmouth Medical School, has discovered that chronic pain is often triggered by a response from the immune system. When DeLeo used mice that were missing a specific type of immune receptor, the mice proved less vulnerable to pain’s lingering effects. Of course, it has long been recognized that bouts of stress can profoundly alter the nature of immune response. “There are many psychological and social variables that can amplify the experience of pain,” says Dr. Carragee. “You can’t just wield a scalpel and make it go away.”
Mind Over Matter
The moral of these studies is clear: To fix chronic back pain, doctors have to look above the neck. Just as MRI and CT scans have enhanced doctors’ understanding of the spine (albeit not in the perfect way they had anticipated), powerful new brain-imaging tools are shedding light on how chronic pain affects both the structure and function of the mind and offering a glimpse of future treatments.
Imagine you are a patient with serious back pain, and when you walk into your doctor’s office, instead of doing the usual physical exam and patient interview, he tells you he is going to study your mind by using an fMRI (functional magnetic resonance imaging) machine, which measures brain activity. He barely glances at your back. By simply examining a few variables inside your head—the size of certain brain regions, the concentration of certain brain chemicals—he would be able to predict about 80 percent of the individual variance associated with your chronic back pain. In other words, he’d have a rather accurate sense of how intense your pain is and how long you’ve been suffering. He would recommend treatments that block or compete with the patterns of brain activity associated with chronic pain or recommend psychological therapy. In contrast, the conventional method of diagnosis, which involves studying the spine, can explain only about 25 percent of patients with back pain. When it comes to diagnosing chronic back pain, the brain reveals more than the body.
A. Vania Apkarian, PhD, is a professor of neuroscience at Northwestern University. He has been studying the neural underpinnings of chronic pain for more than 20 years. In 2004, he published a paper demonstrating that chronic back pain appears to cause brain damage. For each year of agony, people lose about a cubed centimeter of gray matter. With time, it adds up: Apkarian found that subjects with chronic back pain had anywhere from 5 percent to 11 percent less gray matter than control subjects. The suffering is literally toxic.
In a 2006 paper published in
The Journal of Neuroscience, Apkarian’s lab located the specific brain areas triggered by chronic back pain. The scientists found that chronic pain—unlike acute pain—activated brain regions typically associated with negative emotions, thus providing further evidence that chronic pain is really an emotional disorder. It’s a malfunction of the second pain pathway. “It’s as if people with chronic pain have internalized the pain,” says Apkarian. “It has become part of who they are. That’s why you can’t just treat the body.”
