Chronic pain is variously defined as (1) pain lasting more than 3 months, (2) pain lasting more than 6 months, and (3) pain lasting beyond the period of expected healing or persisting in the absence of injury. Chronic pain is distinguished from acute pain in a number of ways. Most concretely, it lasts longer. In many cases, though, what is genuinely unique about chronic pain is that it seems to persist even when a physical insult is not occurring, or it is out of proportion to the physical damage that has occurred.
Pain is an extraordinarily complex phenomenon. At first glance, it appears to be a simple sensation, a message passed to the brain by a peripheral nerve that has received a signal of tissue injury. Upon further examination, though, it becomes clear that what most people describe as pain is much more than a simple sensation. When people say the word “pain,” they are generally referring to the suffering that is associated with a particular physical sensation. In the case of chronic pain, when the sensation often is not an accurate signal that a physical injury is occurring, the distress or the aversion to the sensation might accurately be described as the actual problem with pain. Sensations themselves can betranslated in the brain in any number of ways and can lead to a wide array of emotions. These emotions typically lead to associations and thoughts. If the evaluation of a sensation is aversive and appraised as a threat, the emotions that arise in response to it will typically be unpleasant emotions including fear, anxiety, anger, despair, frustration, or hatred. The related thoughts, which can often become catastrophic stories about the future, then perpetuate the suffering of the individual independent of the original sensation. These thoughts and emotions then lead to coping behaviors, which, in sufferers of chronic pain, often include decreased physical activity, social isolation, and avoidant behaviors, all of which deepen the suffering.
This complex web of phenomena: sensation, translation, emotion, thoughts, and behavior patterns, provides the treatment team with a multitude of potential therapeutic targets. Treatment might target the origin of the physical sensation itself, the transmission of the signal, the interpretation of the sensation in the central nervous system, the emotional reaction to that interpretation, the thought patterns that result, or the habitual behaviors. Each of these areas is an independent source of suffering, and improvements in any of them will address at least some part of the patient's distress.
There are many kinds of chronic pain. In some disorders, the primary source of suffering appears to originate in a clear pain-generating pathophysiology. Inflammatory arthritides such as rheumatoid arthritis, or invasive cancer are examples of this category of chronic pain. In other disorders, such as somatoform disorder or conversion disorder, the primary source of suffering appears to be almost entirely emotional or cognitive. In between these extremes lie the ...