WHAT IS PAIN?

• Acute pain
• Chronic pain
• Neuropathic Pain
• Mechanical pain
• Inflammatory and chemical pain
• Somatic pain
• Visceral pain
• Ischaemic pain

There are two definitions for pain that are widely used.

"Pain is what the person says it is, existing when and where the person says it does." (McCaffery & Beebe, 1999)

Margo McCaffery is a Nurse Consultant who has published widely about pain medicine. What she is saying here is that pain is individual to the patient, the best judge of the intensity of the pain is the patient, and that the patient should be believed. This definition of pain is taught to all nursing and medical students.

The International Association for the Study of Pain (IASP) defined pain as:

“An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” (IASP, 1979)

The importance of this definition is that it includes pain that may occur without any recognised stimulus, and it also introduces recognition that pain is influenced by our emotions.

These definitions should be used to inform the pain medicine practice of all health care professionals.

There are other ways of defining pain. Often it is said to be Acute or Chronic.

Acute pain can be defined as pain that lasts less than 6 weeks, or pain that is directly related to tissue damage. The pain that is experienced from a paper cut or from standing on a tack is acute pain. Pain that is felt after an operation is acute pain; it is severe, but we expect it to go away.

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Chronic pain is pain that lasts longer than 3 months. There are at least two different types of chronic pain problems — pain that has an identifiable cause, (an injury), and pain with no longer an identifiable cause (the injury has healed). Most of chronic pain is of musculoskeletal origin.

Chronic pain with an identifiable cause includes conditions like spinal stenosis, degenerative disc disease, or chronic leg ulcers. These can cause ongoing pain until the underlying cause is successfully treated. If the pain caused by these types of conditions has not subsided after a few weeks or months of conservative treatments, then surgery may be considered as a treatment option. Chronic pain with no identifiable cause continues beyond the point of tissue healing and there is no clearly identifiable pain generator that explains the pain. It is often termed ‘chronic benign pain’. It appears that pain can set up a pathway in the nervous system and, in some cases, this becomes the problem in itself. In chronic pain the nervous system may be sending a pain signal even though there is no ongoing tissue damage. The nervous system itself misfires and creates the pain. In such cases, the pain is the disease rather than a symptom of an injury. The term “chronic pain” is generally used to describe pain that lasts more than three months, or beyond the point of tissue healing. Chronic pain is usually less directly related to identifiable tissue damage and structural problems. Examples of chronic pain are: chronic back pain without a clearly determined cause, failed back surgery syndrome (continued pain after the surgery has completed healed), and fibromyalgia.

Chronic pain is influenced by many factors, such as ongoing pain signal input to the nervous system even without tissue damage, physical weakening due to lack of exercise, a person’s thoughts about the pain, as well as emotional states such as depression and anxiety. Chronic pain is much less well understood than acute pain.

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Neuropathic Pain There is also a category of pain called neuropathic pain (also called nerve damage pain or neuropathy). While it is a chronic pain, it is very different from pain caused by an underlying injury.

Neuropathic pain has only been investigated relatively recently. In most types of neuropathic pain, all signs of the original injury are usually gone and the pain that one feels is unrelated to any seen injury or condition. With this type of pain, certain nerves continue to send pain messages to the brain even though there is no ongoing tissue damage.

Neuropathic pain feels different from musculoskeletal pain and is often described with the following terms: severe, sharp, shooting, stabbing, burning, cold, numbness, tingling or weakness. It may be felt travelling along the nerve path from the spine down to the arms and hands or legs and feet. It is important to understand and diagnose neuropathic pain because it has very different treatment options from other types of pain. For example, some common painkillers are usually not effective in relieving neuropathic pain (though paracetamol is). Treatments for neuropathic pain include different painkillers, nerve block injections, and a variety of interventions generally used for chronic pain that your Pain Medicine Consultant will discuss with you.

Other terms used to describe or define pain include mechanical, inflammatory, chemical, somatic, visceral, referred and ischaemic.

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Mechanical pain is back or neck pain from tissue damage which is caused by putting abnormal stress and strain on the muscles which support the vertebral column.

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Inflammatory and chemical pain are used to refer to pain that is in response to an insult to tissue at a cellular level. Damage to the cells leads to chemicals being released that activate pain receptors locally at the site of injury and causes an inflammatory response.

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Somatic pain refers to pain that originates from ligaments, tendons, bones and blood vessels. Because there are not many pain receptors in these areas, the pain is often described as a dull ache.

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Visceral pain refers to pain felt in the organs of your body. Because there are even less pain receptors in your organs, the pain is more aching and can be difficult to pin point. It can often cause referred pain, which is pain that is felt somewhere other than the where it originates.

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Ischaemic pain can be very severe and is caused by a reduction in blood flow, commonly felt in legs but it could occur anywhere. It is a sign that your muscles are not getting enough oxygen. Chest pain caused by a heart attack is an ischaemic pain.

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