“What do you mean the scan showed nothing, there must be something wrong…” This is something that we hear a lot from people who have persistent pain with no identifiable tissue injury.
X-rays, CT scans, MRIs, Bone Scans, etc are important tests in modern day health care. They are able to detect many tissue issues from small stress fractures, muscle tears, tumors and disc herniations to name a few. These tests can be very helpful, however, what they do not show us is pain. Sometimes these tests lead us down the wrong path, chasing after structures that have nothing to do with your pain.
There have been numerous studies of patients having various tissue issues such as torn cartilage, bulging discs, spinal stenosis and osteoarthritis on imaging, yet no pain. This is not a small number, in some studies, up to 60% of people tested have tissue issues yet no history of pain in the area. We also know that as we age these tissue issues become more common in all of us, pain or no pain.
On the other hand, there are people that have severe pain yet nothing on any imaging tests. Does this mean that people with no tissue issues are making their pain up?
Of course not!
We know that some people can have pain alongside tissue damage (such as sprains or strains) and the pain resolves when the tissues heal. Other people have degenerative diseases such as rheumatoid arthritis and osteoarthritis but again, the level of degeneration does not always match the pain intensity. Others can continue to suffer from severe pain from a minor injury that has healed completely.
How does this happen?
First, we must acknowledge that pain and tissue injury do not correlate well. Pain is more complex than just a result of injured or damaged tissues. If we take the definition of pain from the International Association for the Study of Pain we see that pain is:
“An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”
Two very important acknowledgements in this definition are the ‘emotional experience’ and the ‘potential damage’. This describes that pain can occur without actual damage or after the damage has resolved and also that pain has a very real emotional effect.
Typically, when a body part is injured, specialized sensing nerves called nociceptors become excited and send a signal to the spinal cord where they talk with a second nociceptor. If this message is strong enough, the second nociceptor then sends the message up to the brain warning us of the danger. This can even happen when there is no damage and is part of our body’s protective mechanism.
This is where things start to get complicated. This second nociceptor can become excited and send danger signals up to the brain even if the initial nociceptor is not talking very loudly or has even stopped talking altogether. Thoughts, expectations, stress, anxiety, changes in mood are just some of the things that can cause this second nociceptor to get excited and send off messages. These factors can also increase activity in other key areas of the brain that are responsible for creating the pain experience.
As pain persists, there can be some structural changes in the nerves; this could be likened to faulty electrical wiring in a house. In this case, the structural changes promote danger signals so that the brain is receiving faulty messages about the status of the tissues and other inputs such as movement, touch and temperature.
To add to the complexity, nociception does not always lead to the brain creating pain, and pain can occur without nociception. Thus some tissue issues may be activating nociceptors but you feel no pain and vice-versa. The ultimate job of the brain is to try and interpret these messages, process them along with other important information and either produce a protective pain experience or not. Sometimes, a brain does all the necessary things to create lots of pain despite the level of tissue issues.
Managing and treating persistent pain is best done by an interdisciplinary team approach including physicians, physiotherapists, psychologists, and occupational therapists that understand persistent pain. After any serious health conditions are ruled out, learning about the factors involved in your pain and what increases your pain is key. Then treatment can begin to address these factors and help you improve your function and pain.
Roland Fletcher, Registered Physiotherapist
Dr. Aaron MacINNES, Anesthesiologist and Pain Specialist