brain, spinal cord, and nerve disorders
Chronic Pain
Introduction
Chronic pain is pain that lasts or recurs for months or years. Usually, pain is considered chronic if it does one of the following: Lasts for more than 3 months Lasts for more than 1 month after the injury or problem that originally caused pain has resolved Recurs off and on for months or years Is associated with a chronic disorder (such as cancer, arthritis, diabetes, or fibromyalgia) or an injury that does not heal (See also Overview of Pain .) Chronic pain sometimes occurs when nerves become more sensitive to pain. For example, the original cause of the pain may repeatedly stimulates the nerve fibers and cells that detect, send, and receive pain signals. Repeated stimulation can change the structure of nerve fibers and cells (called remodeling) or make them more active. As a result, pain may result from stimulation that might not ordinarily be painful, or painful stimuli may seem more severe. This effect is called sensitization. Also, areas of muscle or connective tissue may become very sensitive and tender to the touch. These areas are called trigger points because touching these areas frequently triggers unexplained pain that radiates to other areas of the body. Chronic pain sometimes occurs when the original cause of the pain stimulates nerves repeatedly and such stimulation can physically change the nervous system in ways that make the pain worse and last longer. Chronic disorders (such as Overview of Cancer , Anxiety, depression, and other psychologic factors may help explain why some people experience pain as more unpleasant than others do and why pain limits their activities more. For example, people with chronic pain know it will recur and may become fearful and anxious as they anticipate the pain. Fear and anxiety can reduce the production of substances that reduce the sensitivity of nerve cells to pain. These changes in sensitivity to pain partly account for pain that persists after its cause resolves and for pain that feels more severe than expected. Sometimes what originally caused the pain is obvious—for example, when people have had an injury that resulted in chronic back pain. Or the cause may be unknown—for example, when people have a chronic headache. 