Persistent pain is a newer term being used in place of “chronic pain.” Nearly all of the physical therapists at Alpine Physical Therapy took part in the 6th annual Montana Pain Initiative Conference, a two-day conference held at the University of Montana on May 30th and 31st. This year’s conference was titled “Treating Pain: Neuroplasticity and Team Care in an Evolving Healthcare System.” Resultantly, we thought it would be appropriate to include a recent literature review on the topic. It’s a bit lengthier than most of our blog posts, but it’s well worth the read.
Chronic pain is constant pain that lasts long after the expected time frame of healing. For instance, if you roll your ankle you would expect that ankle to be painful for the length of time that it takes for the ligaments and tendons to heal—say a week or so depending on the extent of the sprain. If there was an underlying chronic, or persistent pain, component then your ankle might still hurt six months after the injury, long after the actual tissue damage has corrected itself.
To understand why the pain that people feel is very real we need to look at how we actually feel pain. For 400 years the medical model for understanding pain was simple: when you step in a flame the sensors in your feet feel the pain and a pain signal is sent via nerves to your brain which shouts Tissue is being damaged! Move your foot! Then in the 1960s this model was proven to be much more complicated. Instead of one continuous pathway (foot to brain), there is a pathway going up with three junctions (at your limb, at your spine, and in your brain) and a pathway going down with the same junctions. Each of these junctions interprets pain and can do so in multiple ways via pain sensors.
At the level of your limbs there are two types of pain sensors, which are then further divided into sub categories. Each of these categories is responsible for a different type of pain detection such as hot or sharp. They also each transmit signals to the spine at varying speeds. This explains why when you accidentally touch something hot you quickly pull back your hand but when your leg falls asleep from sitting you do not notice for a while. To make things more complicated, one category of these pain sensors (known as C fibers) sends signals very slowly with generalized information in regards to pain location and are extra sensitive to inflammatory chemicals that your body creates to help to heal itself. As an example, C fibers are responsible for that achy pain you might have after rolling your ankle; the pain is in your foot and a little up your calf even though the tissue damage might only be at the outside of your ankle. Luckily, C-fibers respond well to NSAIDs like ibuprofen so you take a few of these and the pain signals being sent from your ankle to your brain are quieted as the inflammation decreases.
Pain sensors at the next level, your spine, are more complicated. The sensors here are the go-between from your limbs to your central nervous system (think brain and spinal cord). The caveat is these pain sensors can be ignored by your brain. For instance, if you are in a house fire you grab your baby and run out of the house before you realize that your arm is burned. Your arm is obviously hurt, but you didn’t feel it at the time because of your brain sending a message down to your spine pain receptors saying, Override, there are more important matters at hand!
The highest levels of pain sensors are in your brain in multiple locations. At each of these locations pain is controlled by complex relationships between emotions, brain chemicals, and the nerve matrix itself. Your brain determines what pain you acknowledge and what pain you ignore.
Remember that there are three levels of pain sensors going in both directions? If our brains responded to all of the pain sensors signals at all three levels imagine how much information that would be. A key piece to a healthy pain response is for our brain to recognize which signals are important to acknowledge and which ones we should ignore. Or, which signals are telling us that there is actual tissue damage occurring, and which ones are simply saying, this surface is lukewarm.
In people with persistent or chronic pain, their pain response system at one of those three levels has lost the ability to send accurate signals or ignore signals all together. In other words, the communication lines are crossed and even though there is no tissue damage occurring that person is feeling very real pain. Psychotherapy, relaxation techniques, and rehabilitation (physical therapy or occupational therapy) to down-train the hypersensitivity of the pain sensors are all ways the muddled pain system can be addressed without drugs at the brain level and are often rather effective since the brain is the control center of the pain itself.
Drug management of chronic pain is complicated and controversial. NSAIDs (i.e. ibuprofen), aspirin and acetaminophen (i.e. Tylenol) have mixed effects for treating chronic pain depending on pain location. Long-term use of NSAIDs can cause issues in your stomach and intestines. Opiates and opioids (most commonly morphine) has been the standard drug prescribed. This drug class acts at all three levels of pain sensors. The catch is three fold: you develop a dependency, require higher and higher doses, and suffer side effects as a result. Long-term use studies (>6 months) show that opiates lose their effectiveness over time so it is not recommended to take them long term.
More promising are drugs that address the pain at the control center itself: your brain. These drugs include:
1. Anticonvulsants (i.e. gabapentin and carbamazepine)
2. Antidepressants (which low doses address both depression as well as diminish the pain signals being sent)
3. Tramadol (acts similarly to anticonvulsants and antidepressants but can cause many of the same side effects as opiates).
4. Muscle relaxants (i.e. cyclobenzaprine, tizanidine, both which do not have evidence to support the effectiveness of long term use)
More location specific treatments include creams or patches placed on your skin at the pain location such as lidocaine or NSAID patches.
Moderate evidence exists for non-invasive treatment strategies, which include transcutaneous electrical nerve stimulation (TENS) (this confuses your pain sensors and decreases pain by wearing sticky pads with mild current flowing to your skin), hot or cold packs, and acupuncture. Spinal injections or nerve blocks are yet another way to help to manage pain but have mixed results as well.
However, no matter what drug options are used, it should be noted that the most effective way to treat persistent pain is in utilizing multiple approaches and calling on a team of health care providers to help to restore a person’s overall function.
Richard L. Uhl, MD, et al. Management of Chronic Musculoskeletal Pain. In Journal of American Academy of Orthopedic Surgery. February 2014. Vol 22, No 2. Pp 101-110.