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.