## Basic introduction
- The subcommittee on taxonomy of the International Association for the Study of Pain (IASP) defined pain as “unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”[a]
- McCaffery's 1968 definition of pain is that 'Pain is whatever the experiencing person says it is, existing whenever he says it does”[b]
- Poor management of pain can result in[c]:
- Decreased physical and mental functioning
- Pain that lasts for more than 3 months despite the treatment efforts is said to be chronic pain
## Pathogenesis of pain
- Depending on the clinical characteristics, pain can be categorized generally into:
- Idiopathic pains.
- Nociceptive pain
- is transmitted via classical pain receptors (also known as nociceptive receptors)
- These receptors can be excited by thermal, mechanical and chemical stimuli to produce:
|||Visceral pain (that is usually “referred” pain)
|||Deep somatic pain (that is poor localized and dull)
|||Superficial somatic pain (that well localized and sharp).
- Neuropathic pain
- Results from conditions that affect any part of nervous system
- When peripheral nervous system is affected the resultant pain is usually described with various words such as “pins and needles”, “burning,” “tingling,” “electrical,” or “stabbing,”
- Psychogenic pain
- Also known as psychalgia or somatoform pain
- It results from mental, emotional, or behavioral factors.
- Phantom pain
- It is a form of neuropathic pain from a part of the body that has either been lost or from which the brain no longer receives signals.
- Breakthrough pain
- It is a form of pain that occurs in between two dose intervals of analgesics
- With selective COX-2 inhibitors such, as celecoxib and meloxicam, inhibition of COX-2 provides therapeutic effects, as with other NSAIDs.
- COX-1 activities responsible for gastric and renal side effects with NSAIDs are not markedly affected by COX-2 hence they cause fewer incidences of related side effects. Their main drawback is that they increase risks of thrombotic events such as myocardial infarction and stroke.
- Management of pain needs to start with non-opioid analgesics and climb up the ladder to powerful opioids (as per the WHO analgesic ladder for cancer pain)
- Other methods of management of pain include: