Unravelling the mysteries of chronic pain

What is chronic pain?

In a nutshell chronic pain is pain which has persisted for more than six months. It can be notoriously difficult to treat, and many patients find they try one thing after another and nothing has a lasting effect. There is no doubt that chronic pain is difficult to fix. The reason for chronic pain being so challenging is that it is a very complex phenomenon.

Even acute pain, such as we experience when we tread on a nail or burn a finger on the iron, is more complex than was previously thought. Pain is always a product of the brain processing the information at its disposal. This will include nerve impulses from the injured part, but also thoughts, feelings and memories which may attach themselves to the sensation. If you are a cellist or a violinist, you may understand that a burn to the fingers of your left hand will be perceived as more serious than if it was your right hand – because it is the left hand that does the fingering.

However in the case of chronic or persistent pain, the complexity increases probably tenfold or more. It has long been known that patients who are afraid of pain or who feel less in control of their lives will actually experience higher levels of pain than those who are less fearful and feel more in control. More recent research suggests that understanding pain mechanisms also helps to diminish the intensity of the pain.

So any practitioner working with a patient with chronic pain will find they are more effective if they “Explain Pain.” This is a relatively new approach to working with chronic pain and is the brainchild of two Australian neuroscientists, David Butler and Lorimer Moseley, the founders of the Neuro-Orthopaedic Institute or NOI. What follows is largely based on research and concepts laid out in their excellent book, Explain Pain.

What is pain for and why is it not always a good measure of what’s wrong?

Pain is an alarm system – it exists to let you know that there is something wrong. You would therefore be forgiven for assuming that the more severe the pain, the greater the danger. However there isn’t always such a simple correspondence between the severity of the injury and the severity of the pain. In fact it is the brain which decides whether something hurts or not – 100% of the time. And the brain takes account of considerably more than the severity of the injury.

In “deciding” how much pain is appropriate, the brain relies on context: memory, reasoning and emotion. Before producing the experience of pain, the brain must decide whether this is the best course of action. For instance in the phenomenon of battlefield anaesthesia, a soldier may have lost all or part of a limb, but will not experience pain until he is out of danger from the enemy as escape from the battlefield is the highest priority at this point.

In his book, Painful Yarns, Lorimer Moseley recounts an incident when he was out walking and felt a scratching sensation just above his left ankle. Assuming the scratch came from a grass stalk, he flicked his ankle, and carried on walking, without feeling any pain – because the brain did not perceive any danger. However it turned out that the scratch was actually a snake bite, and Moseley was lucky to survive as this was an Eastern Brown, which has a lethal venom. About six months later, Moseley was out walking again and experienced a prickling sensation on his left leg. The pain was immediate and intense and shot up his leg “like an electric bolt”. He doubled up and fell over, but when he stopped to examine his leg he realised that it had just been scratched by a twig!

Explain Pain details other pain phenomena which are even stranger, including phantom limb pain (pain experienced as if it emanates from a limb which has been amputated); couvade, in which men experience the pains of childbirth when their wives are in labour; and the fact that the effectiveness of aspirin depends on its shape and colour. Butler and Moseley identify four types of “ignition cues” for pain:

  • emotional state: distress lowers the threshold for pain and a stressful situation such as being bullied at work may lead to tissue changes (eg tension in shoulder muscles) which may themselves contribute to pain levels
  • the perceived cause of the pain: when women who have had a mastectomy get breast pain, the pain feels more intense if it is perceived as returning cancer than it is if the pain is perceived as being due to another cause
  • knowledge and understanding: the less knowledge you have about a medical procedure, the more pain you will experience during the procedure and afterwards
  • action: I know from my own clinical experience that pain often diminishes once the patient has made an appointment to come and see me. The brain stops the pain once you have acted on it, because it knows that you have listened to the alarm signal.

How does pain work and how does it get modified by the brain?

sensory nerve cell

Fig 1. Sensory nerve cell

There are good physiological reasons for how pain perception gets modified by these ignition cues. Pain messages start with nociceptors. These are specialised sensory nerve cells with sensors for temperature, pressure and chemicals (see fig 1). If enough sensors are activated, the nerve will fire, sending an electrical impulse which travels up its length to its terminus in the spine at an area called the dorsal horn. Here it connects with a second order nerve which relays the information to the brain. However there are other nerves which terminate in the dorsal horn and . These include neurones coming down from the brain, which may either dampen the pain signal in the second order nerve, or enhance it making it stronger. In other words the brain can turn the volume up or down on the second order nerve.

This strengthening of the signal in the second order nerve occurs by a process of sensitisation in the spine. This can lead to hyperalgesia (where a mild pain is felt as being much stronger), and allodynia (where even a light touch can seem painful). So we could say that the volume gets turned up on the second order nerve, so that it appears that things are worse than they really are, and this is what often happens in chronic or persistent pain.Unfortunately similar things happen in the brain. The part of the brain which is responsible for sensation (including pain) is known as the somatosensory cortex or homunculus (see fig 2) and it is divided into areas corresponding to different body parts.

The somatosensory cortex

Fig 2. The somatosensory cortex – or homunculus Attribution: By OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

The areas of the homunculus which correspond to body parts which have high sensitivity such as hands and tongue are larger than those which correspond to parts like the feet which have low sensitivity. In chronic pain, changes take place in the sensory cortex leading to increased sensitivity and widening of the area reacting to pain signals.

However it is not just the somatosensory cortex which is involved in producing the experience of pain. Many other parts of the brain are involved too. These brain areas form a network which is sometimes referred to as the “pain matrix.” Different areas in this matrix seem to play different roles in the experience of pain. The somatosensory cortex is involved in processing the location of the injury. In other words, it lets you know that it’s your finger, not your toe that is hurt. Other parts of the brain contribute to the emotional and cognitive aspects of the pain sensation. For example, parts of the pain matrix located in the frontal lobes of the brain are important for how one makes sense of pain and for evaluating its significance for our lives. (Will I be able to work after this injury? Does this mean my cancer is coming back?) Other areas – the limbic and insular systems – seem to be responsible for the emotional aspects of pain and its intensity.

Very often by the time pain becomes chronic, the tissues that were injured will have healed. So there may be no good reason to be in pain. It is the hypersensitivity of the brain and nervous system that maintains the pain beyond the point when the tissues have actually healed.

What can be done?

So if chronic pain is so much a product of sensitisation in the brain and spinal cord, what can an osteopath do to help? To some extent there is always work to be done on the tissues. Even though the original injury may have healed, there will still be some tissue changes which need addressing particularly if the patient has developed compensatory patterns. Muscles may be either too weak or may have become shortened. Joints may have stiffened up due to disuse.

Secondly patients will recover better if they understand pain mechanisms and can be encouraged to fear pain less and do more. So part of my role as an osteopath is to help my patients understand better what is going on when they experience chronic pain and to encourage them to be less fearful and to try doing some of the things they have stopped doing because of their fear of pain. A gradual increase in gentle activities can bring about changes in both the brain and the body which reduce the sensitivity of the DRG and thus lead to reductions in pain levels.

There are also specific strategies which will help to get pain under control and turn the volume down on it:

  • meditation and relaxation
  • pacing of activities if the patient is in a boom and bust cycle
  • social contact

I have incorporated these and other approaches to the management of chronic pain into a new programme called BrainWorks.

These are all things the osteopath can encourage: it is all about enabling the patient to take control. And the relationship between therapist and patient is also important. So if you like and trust your therapist (be they an osteopath, chiropractor or massage therapist) and they can “explain pain” to you then half the work of treatment is done.

Remember knowledge is power – and pain relief!!

 

Notes:

1. Cynthia Lee, McGill University. Chronic pain changes our immune systems.

Categories: Back health, chronic pain, dorsal horn, Explain Pain, Health and Wellbeing, low back pain, neck and shoulder pain, Osteopathy and Pain mechanisms.

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