PAIN CLINIC

Pain: An unpleasant sensation that can range from mild, localized discomfort to agony. Pain has both physical and emotional components. Pain is perceived in the cerebral cortex area of the brain and is always subjective.

Classification of Pain

Classification of pain: Classifying pain is helpful to guide assessment and treatment. There are many ways to classify pain and classifications may overlap. The common types of pain include:

1. Nociceptive: represents the normal response to noxious insult or injury of tissues such as skin, muscles, visceral organs, joints, tendons, or bones. Nociceptors are nerve endings that detect and respond to painful or unpleasant stimuli.

• Somatic: musculoskeletal (joint pain, myofascial pain), cutaneous; often well localized
• Visceral: hollow organs and smooth muscle; usually referred
  2. Neuropathic: pain initiated or caused by a primary lesion or disease in the somatosensory nervous system.
• Sensory abnormalities range from deficits perceived as numbness to hypersensitivity (hyperalgesia or allodynia), and to paresthesias such as tingling.
• Examples include, but are not limited to, diabetic neuropathy, postherpetic neuralgia, spinal cord injury pain, phantom limb (post-amputation) pain, and post-stroke central pain.
  3. Inflammatory: a result of activation and sensitization of the nociceptive pain pathway by a variety of mediators released at a site of tissue inflammation.
• The mediators that have been implicated as key players are proinflammatory cytokines such IL-1-alpha, IL-1-beta, IL-6 and TNF-alpha, chemokines, reactive oxygen species, vasoactive amines, lipids, ATP, acid, and other factors released by infiltrating leukocytes, vascular endothelial cells, or tissue resident mast cells
• Examples include appendicitis, rheumatoid arthritis, inflammatory bowel disease, and herpes zoster.

Pathological processes never occur in isolation and consequently more than one mechanism may be present and more than one type of pain may be detected in a single patient; for example, it is known that inflammatory mechanisms are involved in neuropathic pain.

• There are well-recognized pain disorders that are not easily classifiable. Our understanding of their underlying mechanisms is still rudimentary though specific therapies for those disorders are well known; they include cancer pain, migraine and other primary headaches and wide-spread pain of the fibromyalgia type.

Pain can also be classified according to duration of the time:

1.       Acute pain- the feeling of such pain is for a short time usually. It may take a day or less than 3 months. It is caused by internal or external injury or disease. It warns the individual that harm or damage is occurring   stimulates them to take avoiding or protective action. With effective treatment of disease or injury and/or the natural healing process, the pain resolves – although some acute pain syndromes may develop into chronic pain. Stimuli which are sufficiently intense potentially to damage tissue will cause the stimulation of specific receptors known as NOCICEPTORS. Damage to tissues releases substances which stimulate the nociceptors. On the surface of the body there is a high density of nociceptors, and each area of the body is supplied by nerves from a particular spinal segment or level: this allows the brain to localise the source of the pain accurately. Pain from internal structures and organs is more difficult to localise and is often felt in some more superficial structure. For example, irritation of the DIAPHRAGM is often felt as pain in the shoulder, as the nerves from both structures enter the SPINAL CORD at the same level (often the structures have developed from the same parts of the embryo). This is known as referred pain. The impulses from nociceptors travel along nerves to the spinal cord. Within this there is modulation of the pain ‘messages’ by other incoming sensory modalities involving natural opioids (that is, endorphins and encephalins) among many others. They are pain transmitting and pain modulating substances in the brain.  The modified input then passes up the spinal cord through the thalamus to the cerebral cortex. Thus the amount of pain ‘felt’ may be altered by the emotional state of the individual and by other incoming sensations. Once pain is perceived, then ‘action’ is taken; this involves removal of parts of the body from the source of pain.

2.        Chronic pain- it is persisting pain or recurrent pain that can last for months to years. Chronic pain differs from acute pain: the physiological response is different and pain may either be caused by stimuli which do not usually cause the perception of pain, or may arise within nerves or the central nervous system with no apparent external stimulation. It seldom has a physiological protective function in the way acute pain has. Also, chronic pain may be self perpetuating: if individuals gain a psychological advantage from having pain, they may continue to do so (e.g. gaining attention from family or health professionals, etc.). The nervous system itself alters the sensitivity to pain so when pain is long-standing in such a way that it becomes more sensitive to painful inputs and tends to perpetuate the pain.