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How Does Acute Pain Become Chronic?

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Woman holding her headChronic pain is a major medical problem, affecting as many as 100 million Americans, robbing them of a full sense of well-being, disrupting their ability to work and earn a living, and causing untold suffering for the patient and family. This condition costs the country an estimated $560-635 billion annually—a staggering economic burden [1]. Worst of all, chronic pain is often resistant to treatment. NIH launched the Grand Challenge on Chronic Pain [2] to investigate how acute pain (which is part of daily experience) evolves into a chronic condition and what biological factors contribute to this transition.

But you may wonder: what, exactly, is the difference between acute and chronic pain?

Acute pain is an intensely unpleasant sensation transmitted by the nervous system to alert you to a real or impending injury—like a bruise, cut, or burn—or an infection like a toothache. It’s a warning that something’s wrong with your body, and that you need to take action. It can trigger you to remove your hand from a hot stove or to get rid of that pair of shoes that make your feet hurt every time you wear them. Pain is a powerful protective mechanism: those who cannot feel it, whether from a genetic condition or from an acquired disease of peripheral nerves like leprosy, suffer very serious consequences. But normally, acute pain is short lived—when the injury has healed, the pain is gone.

But in some situations, this acute pain becomes chronic, persisting for months or even years. In many instances that happens because the physiological condition is ongoing and unresolved—as in cancer or arthritis. But in some instances, the pain doesn’t appear to be caused by any disease, injury, or detectable damage to the nervous system [3]. That pain is just as real to the person suffering from it, though it is referred to as psychogenic pain.

We currently treat chronic pain with a variety of therapies, including medications, electrical stimulation, and surgery. Medications range from relatively mild over-the-counter drugs like aspirin to more powerful prescription drugs like Vicodin™ or Percocet™, which act on the brain and spinal cord to relieve pain. But these powerful narcotic drugs can cause serious side effects. They also carry the risk of addiction.

We believe that one key to developing better treatments is to identify signs that acute pain is likely to become chronic. By discovering such markers, we can personalize the treatment of pain. We could provide more aggressive treatments for those at high risk for chronic pain and minimal treatment for those likely to bounce back quickly. This would also help to reduce the risk of abuse and addiction to painkillers.

Here’s one example. We’re funding efforts to understand how the brain perceives a very common problem: back pain. Are there are biological markers that signal which patients’ pain will evolve into a more chronic form? Already, promising new fMRI brain imaging studies can predict which people will suffer from chronic pain after the acute phase [4].

We’re also looking into whether acute pain causes brain changes in certain people that might enhance pain sensitivity and lead to chronic pain. People coping with chronic pain often suffer from several conditions simultaneously—fibromyalgia and temporomandibular joint disorders or irritable bowel syndrome, for example. Is there some common mechanism?

We know there’s a significant difference in the way children, adults, and the elderly react to pain. A paper cut, for example, might cause your 6 year old to erupt in a fountain of tears, whereas most adults would just brush the injury aside. Is that because our wiring changes as we age? It’s an intriguing question, and one that we hope to answer.

We’re also investigating the use of complementary and alternative methods—like massage, acupuncture, herbal remedies, meditation, and yoga—to treat pain separately, or in addition to traditional analgesic treatments [5, 6]. As part of the Grand Challenge on Chronic Pain, we hope to understand the causes of chronic pain better—and ultimately to alleviate the suffering of millions.

References:

[1] Relieving Pain in America: A Blueprint for Transforming Prevention, Care, Education, and Research

[2] Grand Challenge on Chronic Pain

[3] NINDS Chronic Pain Information Page

4] Corticostriatal functional connectivity predicts transition to chronic back pain. Baliki MN, Petre B, Torbey S, Herrmann KM, Huang L, Schnitzer TJ, Fields HL, Apkarian AV. Nat Neurosci. 2012 Jul 1;15(8):1117-9.

[5] NINDS Hope Through Research

[6] Chronic Pain and Complementary and Alternative Medicine

NIH Support: NIH Blueprint for Neuroscience Research; National Institute of Neurological Disorders and Stroke; National Center for Complementary and Alternative Medicine