Thứ hai, 13 Tháng 9 2010 17:05

Types of pain

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(ĐTĐ) - Pain is a very complicated phenomenon and there are many ways of describing and classifying pain.


Most of these are relevant as they provide information about the different clinical aspects of pain


Pain is defined by the International Association for the Study of Pain (IASP) as: "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage". The reason for the rather complicated definition is the need to include patients with chronich pain were the actual physical cause of the pain is unknown.

The definition emphasise that there is both a sensory and an emotional aspect of pain, this is an important concept that has to be keept in mind both in the diagnosis and in the treatment of pain in seriously ill and dying patients.    

Malignant - non malignant pain

The division of pain into malignant and non-malignant pain is based on whether or not the pain is caused by cancer.

Historically this division had a practical purpose, as the use opioids was recommended only in patients with cancer.  This division is no longer valid, as it is recognised that patients with other incurable diseases may also need treatment of the pain with opioids.

In practical terms there is still an important differentiation between:

  • patients with chronic pain without an incurable disease - these patients often have long and complicated pain histories and they are seen by specialists in pain clinics
  • patients with pain due to an incurable or potientially incurable  disease  - the majority have relative simple pain history that can be treated by all doctors with the necessary knowledge.  The few patients with complicated pain should be seen by specialists in palliative medicine.   

Based on temporal onset

Acute pain is defined as: 

"A well defined temporal pain inset, generally associated with subjective and objective signs and with hyperactivity of the autonomic system."

Acute pain occur suddently usually in association with a known trauma and the patient will show the signs of acute pain: sweating, pallor, perhaps nausea and he will often be unable to relax or sleep.    

This is the pain seen in patient with acute conditions that may require acute surgical interventions.

Subacute pain:

Develop over several days, often increasing in intesity with a pattern of progessive pain symptomatology.

This is typical for pain cause by cancer; initially it is just an achebut gradually it increases in intesity and the pain becomes a warning signal to the person.

Episodic pain:

Occurs over shorter periods of time at regular or irregular intervals.

Arthritic pain that comes and goes is an example of episodic pain.

Chronic pain :

Is a pain that has persisted for more than 3 months, it often has a less defined temporal onset. There is an adaptation of the autonomic system and there may not be any objective signs. It is characterised by significant changes in the person's personality, lifestyle and functional ability.

Chronic pain is seen both in patient with and without an incurable disease. It has a profound impact on the person's life (see total pain) on the other hand the symptoms caused by the autonomic system are less apparant.

Phatophysiologically a modulation of the whole nerveous system has taken place, making the generation of pain even more complicated and difficult to treat (see pain theory). This underscores the importance of treating acute and subacute pain before it becomes a more complex chronic pain state.

Patients with continuous pain may also experience changes over time:

Baseline pain:

Is the pain reported as an average pain intesity experienced for the 12 hours or more in a 24 hour periode.

Breakthrough pain:

is a pain more severe than the the baseline pain, there are 3 different types:

Movement related episodic pain also called incidence pain 

For example when a patient who is pain free when seated develop severe pain in his leg when walking.

Non-movement related episodic pain:

For example the patient sitting in a chair who suddently experiences a severe pain shooting down his leg.

End of dose pain:

Pain occuring before the next dose of analgesics is due (see the treatment of pain)

Based on the cause of the pain

Pain can also be divided according to the patophysilogical cause, this classification also gives a clue about how to treat the pain.

Many seriously ill and dying patients experience pains that are due to a combination of paincauses making the diagnosis and treament complex.

Nocioceptive pain:

Is caused by the activation of nocioceptors (receptors in the skin, deep structures and vicera that cause pain upon activation) by a noxious stimulus.

This is the most common sort of pain in seriously ill and dying patients.

Nocioceptive pain is almost always responsive to opioids.

Nocioceptive pain can be divided into:

Somatic pain:

Is caused by the activation of nocioceptors in the skin or the muscle-skelltal system.

Is described as: well localised, sharp, aching throbbing, pressure like.

Examples: bone metastases, post operative pain

Important subgroups of somatic pain are.

Inflammatory pain:

The pain is experienced predominantly when the inflamed site is being moved or thouched. Inflammtory reactions are found in acute trauma, in immunologically derived diseases, in infections and as a component of malignant tumours and metastasis.

Muscular pain

Many patients loose both muular strenght and mass, this may cause the remaining muscles to become strained. Also pain in bone and joints may cause the muscles to contract in order to keep the painfull area as stable as possible.  It will lead to pain in stiffness in the muscles, further strain may cause spasms or cramps.

Visceral pain

Is caused by the activation of nocioceptors in the internal organs or the tissue surrounding them.

Is described as: diffuse, gnawing, crampy, aching, sharp, throbbing. 

Due to: infiltration, compression disstenstionor stretching of thoracic or abdominal organs.

Examples: liver metastasis, the passing of a kidney stone, a heart attach .

Acute viseral pain is often accompanied by symptoms casued by the autonomic system.

A subtype of visceral pain is:

Colicy pain:

Is described as buliding up to a crescendo and then there is a pain free period before the pain builds up again. Its found in patient with ileus* and is often poorly responsive to opioids but respons well to anticholonergic drugs.  

Viseral pain can cause:

Referred pain:

The pain is reffered to a cutaneous site remote from the site of the lesion. The referred cutaneous site may be tender and painfull to touch.

Example: pain in the right shoulder region in cholecystitis.

Neuropathic pain is defined as:

"A diverse group of syndromes in which the sustaining mechanisms for the pain are presumed to be related to aberant somatosensory processes in the periphial nervous system, the central nerveous system or both. ´These pains are often percipitated by overt injury to neural structures but, once etablished, are often far in excess of any overt peripheral patology. a neuropathic pain mechanism increase the likehood of an unfavorable opioid response."

In other words neuropathic pain is:

  • caused by an injury to the periphial or central nervous system.
  • causes a pain that is in excess of the initial injury
  • a significant number of the patient will not become painfree on treatment with opioids alone but will need adjuvant drugs.

It is described as; a base of a constant dull ache with a pressure or vice-like quality. Overlaying this is a pain that comes without provocation and may last from a few seconds to minutes it is described as pins and needles, a burning pain or a stabbing pain like a knife or a needle.

The pain is often described in the area innervated by the nerves that have been damaged. Thus the pain from a tumour in the axillar may cause pain in the arm, hand and fingers.

Neuropathic pain is often associated with changes in the perception of the skin in the affected area, these changes can be described as:

Allodynia: the provocation of pain by a non-noxious stimuli.

Hyperalgesia:a lowering og the threshold for pain and an increase in the response to pain.

Dysaesthesia: an abnormal, unpleasant but not necessarily painful sensation which can be spontaneous or provoked by external stimuli.

Chronic pain in a surgical scar is a typical example of neuropathic pain: There is often an area of decreased sensitivity around the scarm there may be a constant ache in the scar, but the only feature may be a needle like sharp pain that comes unprovoked and only lasts for a short time 

Because neuropathic pain is often less responsive to opioids a classification based on the opioid responsiveness of the pain has been developed. This division is too simple as part and sometimes all the neurpathic pain can be relieved by opioids.

Psychosocial pain (more details in the section on total pain):

It should be kept in mind that most pains have a psychosocial component that becomes stronger the longer the patient suffers from the pain.



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