CANCER PAIN: DEFINITIONS AND CLASSIFICATIONS
The most widely accepted definition of pain is that given by the International Association for the Study of Pain (IASP)1:
- Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Pain is always subjective.
The rider that pain is always subjective is very important and emphasises that pain is a somatopsychic experience; Aristotle alluded to this when he described pain as a "passion of the soul". It emphasises that a variety of different factors may cause or aggravate pain, all of which need to be considered in assessment and treatment.
A more practical clinical definition is:
- Pain is what the patient says hurts. It is what the patient describes and not what others think it ought to be.
The terminology used in the description of pain is complex and may be confusing.
Classifications-Acute and chronic pain
- Acute and chronic pain have different physical signs and psychological associations and require different approaches to therapy.
Acute pain. Acute pain is usually due to a definable acute injury or illness. It has a definite onset and its duration is limited and predictable. It is accompanied by anxiety and clinical signs of sympathetic overactivity: tachycardia, tachypnoea, hypertension, sweating, pupillary dilatation and pallor. These signs, commonly seen in the hospital casualty department, are considered characteristic of a patient 'obviously in pain,. If acute pain indicates progression of cancer (oris thought to by the patient), it may be associated with signs of depression and withdrawal more commonly seen with chronic pain. Patients who are able to be told that their illness and pain are transitory usually exhibit an understanding, positive attitude. Treatment is directed at the acute illness or injury causing pain, with or without the short term use of analgesics.
Chronic pain. Chronic pain results from a chronic pathological process. It has a gradual or
ill-defined onset, continues unabated and may become progressively more severe. The patient appears depressed and withdrawn and, as there are usually no signs of sympathetic overactivity, they are frequently labelled as 'not looking like somebody in pain'. Patients with chronic pain have symptoms of depression with lethargy, apathy, anorexia and insomnia. Personality changes may occur due to progressive alterations in lifestyle and functional ability. For patients with chronic pain of non-malignant origin, the pain is said to lack positive meaning; for patients with chronic pain related to cancer, the pain not only lacks any positive meaning, but it may have definite negative implications with regard to prognosis and life expectancy. Chronic pain related to cancer requires treatment of the underlying disease where possible, regular use of analgesics to control pain and to prevent its recurrence, as well as psychological and social supportive care.
Patients with chronic pain due to cancer need to be distinguished from those with chronic pain of non-malignant origin who may have definite psychological and social problems. Patients with non-malignant pain may exhibit 'pain behaviour' due to dependency on their painful situation and its rewards, and they fail to respond to the supportive care measures and analgesia which will benefit most patients with pain due to cancer. Operant conditioning and similar methods used for patients with chronic non-malignant pain have little place in the treatment of chronic cancer-related pain.
Establishing the dividing line between acute and chronic pain is difficult. For patients with non-malignant pain, chronic pain is said to exist if the pain persists longer than the expected healing time for the injury or illness in question. For patients with documented malignancy, and in the absence of an acute injury or illness which it can be predicted will heal or respond to therapy, pain lasting more than two weeks should be considered as chronic and treated accordingly.
Incident pain. Incident pain occurs only in particular circumstances, such as pain which occurs after a particular movement or on standing. It should be regarded as chronic pain but, because of its intermittent nature, it should be managed with local measures where possible.