Last updated: Mon, Oct 21, 2024
In the medical context, pain is often classified as either acute, sub-acute, or chronic. Acute pain is pain of up to six weeks' duration, sub-acute from six to twelve weeks, and chronic pain is pain that has persisted for more than twelve weeks (three months). The specific duration may vary—chronic pain is sometimes taken to mean pain that has persisted for six months or more—but three months for chronic pain is most common.
Why three months? There seems to be a general view that pain that lasts longer than three months probably isn't caused by whatever injury originally occured. The normal damage/healing processes that we examined in Injury, Inflammation, and Healing ought to have eliminated that pain.1 This view of "chronic" brings together two different concepts.
The first concept is that “chronic” ought to indicate a medically-significant difference from “acute.” Acute pain would be pain deriving from normal injury and healing, while “chronic” would be pain coming from some other cause. Normal medical treatment would be just the thing for the acute case, but other approaches would be needed for the chronic case.
The second concept is that injuries and illnesses have a normal timetable--that is, it is normal, say, for a twisted ankle to heal in X weeks or for a back that has “gone out” to stop hurting in Y weeks.
Both of these concepts are medically useful. It wouldn't make much sense to keep changing bandages after the wound had healed. Not only would it be wasted effort, but it would probably fail to control any ongoing pain. If there is a normal progression and timetable of healing, the wise doctor should be aware of it.
These concepts don't, however, apply very well to whole classes of pathology. An example of this is osteoarthritis. Its pain tends to come and go, especially early in the course of the condition, as it does in many other conditions. Further, since osteoarthritis is a degenerative condition, once it gets bad, it will only get worse. There isn't a change in the nature of osteoarthritis after three months, and there isn't a normal healing time. Another example that doesn't fit well is the “bad back,” which may flare up irregularly over a period of many years before it becomes a serious problem.
Even in conditions for which the acute/chronic distinction makes sense, there are difficulties with a time-based definition of chronicity. Four such problems were suggested by Von Korff:2
These considerations seem to preclude a definition of “chronic pain” that is based on clear medical distinctions. For that reason, we use a generic, rule-of-thumb definition. In most cases pain that persists beyond three months indicates a disease process other than injury-and-healing. In most cases the chronic pain process will have started before its ninety days were up.
Uncontrollable, prolonged pain produces depression, inability to work, and persistent stress. People's beliefs and emotions can amplify or diminish the experience substantially. Prolonged pain is also influenced by the social environment, particularly how significant others, including health care providers, respond to reports of pain.3
Those are some of the burdens of chronic pain, and they're not light. We've looked at the claims made in the second and third sentences above in other sections within the section about The Psychology of Pain, and particularly in Pain, Behavior, and Psychology.
Not all chronic pain is constant, but for some it is. Medical terms for a chronic condition that isn't constant include “episodic” and “recurrent.”
For those whose pain is more than infrequent, the time dimension is very important. For these there may not be any respite from whatever burdens their condition puts on them. (As I think on it, I don't recall being asked about the continuity of my pain by many of my doctors. I wonder whether that is a common experience, and what it may signify?)
For those whose pain is episodic and recurrent, there seems to be a cost alongside the benefits of intermittent relief. That cost is vigilance. We've seen that the pain system of chronic pain sufferers is abnormal. The consequences are not confined to what authors in the field call "exaggerated" pain or "allodynia," depending on the author and the audience. Despite claims of some behaviorists, pain causes effects whether or not it is normal, healthy pain. If your pain is recurrent but you are in a period of relief, you have Damocles' sword hanging above you. If your pain is active, that is, if you are hurting right now, any "pathological" signals coming from your pain system compete for attention with "healthy" signals. (Again, I've seen little evidence that care providers or researchers pay much attention to the cognitive and affective load that this causes to sufferers.)
Chronic pain conditions can have large components of pain that would be called "acute" if they hadn't been going on for so long. Examples include painful joints in osteoarthritic conditions or severe radiculopathy.
However, many chronic pain conditions are predominantly accompanied by pain that is quite different from the A-delta/C fiber pain that accompanies acute injury. Both the physiology and the neurology of this type of pain are sufficiently different from acute pains that it seems to me to be a basic error to lump the two together under the generic label pain. This motivates me to propose a pain typology that distinguishes the two. The distinction provides a more realistic, hence more useful, image of pain than does the generic label "pain." Hence the following section, What is Chronic "Pain"?.
In a certain sense the meaning of "chronic pain" is simpler than all this. A pain condition is chronic because there is no cure. Sections to follow will make the argument that the corrosive effects of pain tend to accumulate or perhaps compound. The effects needn't be strong and the sufferer needn't be weak for considerable damage to accumulate over the years, rather like rust on an old galvanized roof. That's you and me. Rusty.