Pain is a protective mechanism and acts as a warning. If your hand touches a hot surface it triggers a series of impulses from heat-sensitive nerve fibres. The result is a rapid reflex response. Your muscles react and pull your hand away. Although everyone understands what we mean by the word 'pain', it is difficult to define. Pain isn't just physical; it has emotional effects too – making us feel upset or distressed. Pain may, of course, be the result of some kind of injury. In some situations the physical injury is obvious – for example, a cut, a broken bone or a burn. In other situations the 'injury' is internal and is caused by chemicals which the body itself produces, usually, as in most types of arthritis, as the result of a process called inflammation. Our bodies have specialized nerve endings which detect temperature and chemical changes or mechanical stresses. These activate nerve endings which send 'pain' signals via the spinal cord to the brain.

Pain can also be caused when these nerve endings or nerves are permanently damaged and begin to send signals to the spinal cord by themselves. This causes the nerves to react for no reason, or in response to something that would not normally hurt, such as gentle stroking of the skin. This can happen after shingles, severe nerve injury, and some surgical operations, but it can also happen in some people with diabetes. This type of pain often requires different treatments from the pain caused by stimulation of normal nerve endings.

In some instances it is difficult to explain the exact cause of chronic pain and this can add to the distress or anxiety. This is the case with a condition called fibromyalgia, for example. Such conditions are a challenge to both the patient and the doctor. It does not mean the pain is imaginary or 'psychological' (although psychological factors will influence everyone's tolerance of pain). People with this type of pain may be able to get help from their GP, or from health practitioners such as physiotherapists, or from the specialist pain management clinics which are run in some hospitals.

Pain and the brain

The spinal cord has special 'gate' mechanisms. These interfere with pain messages coming from the nerves and may block or deflect them so that the pain information which eventually reaches the brain is slightly altered. These 'gates' can either reduce the strength of the pain message reaching the brain or increase it.

Some treatments for pain are aimed at closing these 'gates' to reduce the sensation of pain – for example, transcutaneous electrical nerve stimulation (TENS), which helps to control some types of pain. Other treatments, including specific drugs, work on the nerve endings themselves to reduce the sensation of pain. X-ray guided injections, such as nerve blocks or epidurals, are also helpful for some people.

The impact of the pain message once it gets through the spinal 'gate' is further changed by even more complex systems in the brain. The pain message can be affected by a number of factors, for example by:

• how much you concentrate on the pain

• enjoyable activities which can take your mind off the pain

• feelings and thoughts and any anxiety or depression (even if the anxiety or depression was present before the pain started)

• drugs which have a direct effect on the brain (and can therefore reduce the impact of pain).

All this information can be used to find new ways of managing pain. These include psychological techniques which help you to concentrate on other aspects of life, or to improve mood or change behaviour. For example, some people with chronic pain stop exercising. As a result they become less fit. This, in turn, leads to too much time being spent resting, when there is little else to think of but the pain and its bad effects on life. By sensible exercise and aiming to get back to work and to leisure activities despite the pain it is easier to cope with the pain, and life can return towards normal. The psychological techniques which are used may include cognitive behavioural therapy.

Source: Arthritis Research Campaign (arc.org.uk)