Modern Theories of Chronic Pain

One of the more interesting recent advances in modern medicine is a new theory about chronic pain. This article discusses how this new theory, the Gate Control Theory of chronic pain, is changing the way chronic back pain may be understood, diagnosed and treated.

The Specificity Theory of Pain

In the 16th century, the French philosopher and mathematician Rene Descartes proposed one of the original theories of pain. His theory proposed that the intensity of pain is directly related to the amount of associated tissue injury. For instance, pricking one’s finger with a needle would produce minimal pain, whereas cutting one’s hand with a knife would cause more tissue injury and be more painful. This theory, the "specificity theory," is generally accurate when applied to certain types of injuries and the acute pain associated with them.

But chronic pain is often quite different, though no less severe, and a more subtle scientific understanding of pain is required to treat it. Unfortunately, many practicing doctors still try to extend the specificity theory to chronic pain cases.

This approach is probably not valid when studying or treating chronic back pain. The theory assumes that if surgery or medication can eliminate the alleged "cause" of the pain, then the chronic pain will disappear. This is very often not true for chronic pain.

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If a doctor continues to apply the specificity theory to a patient's chronic pain problem, the patient is at risk for receiving unnecessary and ineffective diagnostic procedures, drugs and surgical treatment as the search for the patient's "source of chronic back pain" presses on. Ultimately, the validity of a patient's chronic back pain complaints may be challenged if reasons cannot be found and the "treatments" do not work.

Problems with the Specificity Theory and Chronic Pain

Various clinical observations have proven the specificity theory to be inadequate to explain chronic pain. Dr. Henry Beecher, who worked with severely wounded soldiers during World War II, was one of the first doctors to question the theory. He observed that only one out of five soldiers carried into a combat hospital complained of enough pain to require morphine. These soldiers were not in a state of shock, nor were they unable to feel pain. Indeed, they complained when the IV lines were placed.

But when Dr. Beecher returned to his practice in the United States after the war, he noticed that trauma patients with wounds similar to those of the soldiers he had treated were much more likely to require morphine to control their pain. In fact, one out of three civilian patients required morphine for pain from these wounds. Dr. Beecher concluded that there was no direct relationship between the severity of the wound and the intensity of pain.

He believed the meaning attached to the injuries in the two groups explained the different levels of pain. To the soldier, the wound meant surviving the battlefield and returning home. Alternatively, the injured civilian often faced major surgery and a resulting loss of income, diminishment of activities, and many other negative consequences.

Another finding that discredited the specificity theory was that of phantom limb pain. Patients who undergo the amputation of a limb may continue to report sensations or chronic pain that seem to come from the limb that has been amputated. This may include feeling that the limb is still there, or it may be a sensation of chronic pain. Of course, these sensations cannot actually come from the limb since it has been removed. The specificity theory cannot account for these findings since there is no ongoing tissue injury in the amputated limb, which would mean that there should be no chronic pain.

The specificity theory also cannot explain how hypnosis can be used for anesthesia during surgery. Under hypnosis, certain people can evidently undergo significant tissue damage from surgery without experiencing intense pain. This would support the notion that one’s mental state or frame of mind can override the specificity theory. Similar examples of severe pain or chronic pain following relatively minor injuries can also be furnished.