Helping pets to lead happy and healthy lives


What is pain?

The International Association for the Study of Pain [IASP] defines pain as “An unpleasant sensory and emotional experience associated with actual or potential tissue damage…”. The word ‘emotional’ should be taken to include emotions such as anxiety, fear and, eventually, suffering.

So what pain is your pet experiencing? We clearly cannot know exactly what animals experience but, from a humane view, we should assume pain is the same for animals as it is for humans. Whatever the type of pain, it should never be left untreated.

Nervous system – an outline

Nerve endings throughout the body are equipped with specialised ‘detector proteins’ called receptors. These receptors convert environmental information into nerve impulses and, after modification in the spinal cord, these impulses are transmitted to the brain. The brain then distinguishes between touch, hot and cold, mechanical pressure and chemical changes, and whether these are perceived as harmless, or as pain.

There is no single point when acute pain turns into chronic pain. Pain is better thought of as being part of a continuous spectrum. Furthermore, many complex cases may exhibit contributions from all types of pain.

Pain may be arbitrarily classified as follows:

Physiological pain

Standing on a pebble causes a sharp, physiological pain sensation. Physiological pain is proportional to and stops at the end of the stimulus (e.g. following withdrawal of the foot) and protects against potential harm.

Acute, or inflammatory pain

Tissue injury causes inflammation and the sensation of acute pain. Chemicals are released from injured tissue and immune cells, increasing the sensitivity of receptors and amplifying the production of pain signals. Acute, inflammatory pain may be considered protective, as it prevents use of e.g. an injured limb and allows healing, but acute pain should never be left untreated. Acute pain is proportional to the extent of injury and stops after the tissue heals.

Neuropathic pain

Damage to peripheral nerves may lead to neuropathic pain. This is caused by spontaneous generation of impulses in nerves, usually independent of any damage in the tissues they supply.

Chronic pain

Persistent acute pain (from damaged, inflamed tissue e.g. arthritis) and/or persistent neuropathic pain (e.g. from
damaged nerves) set off a chain of events causing structural and functional changes in the nervous system, all leading
to chronic pain. 

These changes amplify signals from receptors, leading to increased pain perception. The changes also distort sensations, causing even the sensation of touch to be perceived as pain. Chronic pain exists when the pain is no longer clearly related to an underlying cause and it serves no protective role for the body.

Early treatment may prevent the transition from acute to chronic pain.

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Fergus Coutts