Acute and Chronic Pain

When reading about pain you have probably heard it described in 2 broad categories, acute and chronic.  What does this mean?  Is it just a difference in how long the pain has been there? Or is something else happening that changes the nature of pain?


In healthcare, acute simply means an illness or injury that is new or has a sudden onset.  Something like a sprained ankle or getting a stomach bug.  Chronic is an injury or illness that has developed slowly or lasts a long time.  Something like diabetes or osteoarthritis.  Pain can be in both categories and even overlap.  You can get an acute pain from twisting my ankle or hitting your head.  You can have chronic pain from an arthritic knee that aches all the time.  You can also have an acute pain from a chronic problem.  If you move that arthritic knee to quickly or with to much force you may experience an acute sharp pain.

Acute pain generally resolves when the painful stimulus is taken away, or an injury has healed.  Remember pain is a protective response.  If you step on a tack, you feel pain to deal with the tack.  Once it is gone the pain is no longer needed.  The same with an injury.  If you roll your ankle and sprain a ligament, you should feel pain.  You don’t want to continue to damage that tissue.  Once the ligament is healed, the pain should subside.

Chronic pain is generally defined as pain that lasts more than 3 to 6 months.  Most injuries should heal within that time frame.  So if pain lasts longer what is happening?  Are the tissues not healing properly? Is damage continuing to happen?

Pain can persist for different reasons.  One reason is that normal healing has not taken place.  This should be investigated.  Sometimes fractures don’t heal properly, injuries were not diagnosed properly, or surgeries don’t do what they are supposed to.  In these situations “chronic” pain may be continuing acute pain as the brain is continuing to protect an injury.  Chronic diseases can also cause chronic pain.  Things like rheumatoid arthritis, nerve damage, or cancer.  These things also should be investigated and ruled out. 

Sometimes, however, all of these things are ruled out.  X-Rays show that bones have healed.  Blood tests are normal.  MRI’s aren’t conclusive. Enough time has gone by that the tissues have healed and yet pain persists.  In these cases chronic pain may be due to changes in how your nervous system is processing pain.  Signals may be detected more easily and amplified.  Your brain may identify signals as more dangerous than they really are and be more protective than it should be.  This process may overlap with the initial acute problem, or be totally independent of it.  Everything may be “normal” as far as the injury occurs, but the pain persists or maybe even intensifies.

Chronic pain is not just acute pain that lasts a long time.  It can become a totally separate entity from an initial problem or injury.  The nervous system actually changes how it processes pain and gets better at it. In the next articles we will see how it does this, and then we will look at ways that we can try to get it to stop doing this and reduce pain.



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