When pain takes over

The path to permanence
One of the mysteries experts are trying to unravel is why some people suffer indefinitely. I didn’t have a single pain-free day for a solid year. Studies show that 5 to 10 percent of people who are injured develop chronic pain. The nature and extent of your injury, of course, play major roles in whether your pain becomes long-term (nerve damage, for instance, poses that risk), but your odds are even greater if you have a genetic predisposition. “When a nerve is damaged, more than 1,000 genes are changed, but some people are born more susceptible to those changes than others, thus making them more likely to suffer,” Dr. Woolf says.

Simply being a woman can leave you more vulnerable. About 60 percent of the 50 million chronic-pain sufferers in the United States are female, partly because sex hormones make some women more sensitive to discomfort than others. If you happen to be sick or hurt at the time of your injury, the chances of your pain lingering may be higher still. Animal studies suggest illness or prior injury can trigger certain immune cells to release pain-amplifying chemicals called proinflammatory cytokines, says Joyce DeLeo, Ph.D., director of the Neuroscience Center at Dartmouth College in Hanover, New Hampshire.

To compare ordinary acute pain to chronic pain, think about the last time you stubbed your toe. The affected nerves sent an electrical message to your spinal cord, which in turn told your brain to feel pain. Your blood pressure increased, and your heart raced. The pain likely lasted for a few days; it was your body’s way of telling you to rest your toe so it could heal.

But an intense injury or illness can cause pain pathways to become overly sensitive, much like a broken car alarm that won’t quit blaring. Your injured tissue may produce inflammatory chemicals, which promote healing but can also sensitize nerve cells bodywide. (This reaction partly explains why taking a warm shower when you have a sunburn is especially painful.) In addition, the brain itself can become overly sensitive. An injury leads to a burst of activity in nerve cells, which bombard the spinal cord with electrical signals, amplifying pain messages to the brain.

The result of hypersensitive nerve cells, whether in the body or brain, is the same: You experience pain all the time, for no apparent reason. Uninjured body parts suddenly become more delicate, and your threshold for pain drops, so things that wouldn’t normally make you flinch (such as a hug or a cool breeze) are uncomfortable. Something that’s always painful — like getting a shot — causes more pain, and longer than usual. All the while, Dr. Woolf says, “there may be no detectable physical abnormality.”

Pain and stress: A vicious cycle
Along with the physical agony, pain can lead to depression. I worry about letting my limitations affect my kids, but it sometimes breaks my heart that I can’t pick them up or even push them in a swing or teach them how to play tennis. Studies show that between 30 and 54 percent of all chronic-pain patients have been diagnosed with clinical depression, and more than half of the rest suffer from one or more depressive symptoms which include fatigue, changes in sleep habits, loss of appetite and overeating. And while pain often brings on depression, research also shows that people who are depressed are more likely to experience an onset of chronic pain.

It’s not surprising that the two conditions, both characterized by feelings of helplessness and sadness, go hand in hand. But there’s also a biological explanation. The same brain chemicals — serotonin and norepinephrine — that are lower than normal in depressed people also ebb in people with chronic pain, says Carol A. Warfield, M.D., chief of anesthesia, critical care and pain medicine at Beth Israel Deaconess Medical Center in Boston. “They may be depleted when pain becomes chronic,” she says. That’s why certain antidepressants, which raise levels of these chemicals, are now used to treat chronic pain.

Of course, not everyone with chronic pain becomes depressed. “There are people who adjust well to the limitations imposed by their pain,” says Joshua Wootton, Ph.D., director of pain psychology at the Arnold Pain Management Center at Beth Israel Deaconess Medical Center. But for those coping with both depression and pain, some new findings offer hope. Alex Zautra, Ph.D., codirector of the Resilience Solutions Group at Arizona State University at Tempe, who studies what makes some chronic-pain sufferers more resilient than others, says people who maintain their usual activities and focus on positive emotions do best. “These people have the same amount of pain but suffer less,” he says.

Being active can also prevent pain from becoming disabling. Many people restrict their regular pursuits such as exercise because they’re afraid of worsening their symptoms, or their primary care doctors advise rest. But sitting on the sidelines only prolongs pain. If you’re inactive for a long period of time, you lose endurance, flexibility and strength. The result: additional pain due to out-of-shape muscles. “It’s important to keep using your muscles, even if some activities hurt,” says Dennis Turk, Ph.D., John and Emma Bonica professor of anesthesiology and pain research at the University of Washington at Seattle. You can feel some pain — the “good” kind that comes with a challenging but not overly taxing workout — without causing injury. “Once your doctor has ruled out a significant problem, like a fracture, you have to begin slowly building yourself up.”

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