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.
In the first part of this chapter, we will explore some of what is known about the nature of chronic pain and try to understand how it is perpetuated and, ideally, how it can be interrupted. In the second part of this chapter, we will discuss specific therapies that are effective in the management of chronic pain.
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 (“hurt does not equal harm”), the distress or the aversion to the sensation might accurately be described as the actual problem with pain. The pain sensations, as real as they are, are created in the brain. They do not simply represent nociception of a peripheral injury. They are better explained as a signal that the body feels it needs to protect itself. The pain sensations themselves can be translated 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 themselves 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 ...