About Pain

Pain Types

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Pain Classification

• Nociceptive Pain arises from the stimulation of specific pain receptors. These receptors can respond to heat, cold, vibration, stretch and chemical stimuli released from damaged cells.
• Non Nociceptive Pain arises from within the peripheral and central nervous system. Specific receptors do not exist here, with pain being generated by nerve cell dysfunction.

• Source - tissues such as skin, muscle, joints, bones, and ligaments - often known as musculo-skeletal pain.
• Receptors activated - specific receptors (nociceptors) for heat, cold, vibration, stretch (muscles), inflammation (e.g. cuts and sprains which cause tissue disruption), and oxygen starvation (ischaemic muscle cramps).
• Characteristics - often sharp and well localised, and can often be reproduced by touching or moving the area or tissue involved.
• Useful Medications - may respond to combinations of Paracetamol, Weak Opioids OR Strong Opioids, and NSAIDs (see Analgesic Flow Chart).

• Source - internal organs of the main body cavities. There are three main cavities - thorax (heart and lungs), abdomen (liver, kidneys, spleen and bowels), pelvis (bladder, womb, and ovaries).
• Receptors activated - specific receptors (nociceptors) for stretch, inflammation, and oxygen starvation (ischaemia).
• Characteristics - often poorly localised, and  may feel like a vague deep ache, sometimes being cramping or colicky in nature. It frequently produces referred pain to the back, with pelvic pain referring pain to the lower back, abdominal pain referring pain to the mid-back, and thoracic pain referring pain to the upper back.
• Useful medications - usually very responsive to Weak Opioids and Strong Opioids.

• Source - from within the nervous system itself - also known as pinched nerve, trapped nerve. The pain may originate from the peripheral nervous system (the nerves between the tissues and the spinal cord), or from the central nervous system (the nerves between the spinal cord and the brain) - see Nerve Pain.
• Causes - may be due to any one of the following processes
• Nerve Degeneration - multiple sclerosis, stroke, brain haemorrhage, oxygen starvation
• Nerve Pressure - trapped nerve
• Nerve Inflammation - torn or slipped disc
• Nerve Infection - shingles and other viral infections
• Receptors activated - the nervous system does not have specific receptors for pain (non nocicpetive). Instead, when a nerve becomes injured by one of the processes named above, it becomes electrically unstable, firing off signals in a completely inappropriate, random, and disordered fashion.
• Characteristics - These signals are then interpreted by the brain as pain, and can be associated with signs of nerve malfunction such as hypersensitivity (touch, vibration, hot and cold), tingling, numbness, and weakness. There is often referred pain to an area where that nerve would normally supply e.g. sciatica from a slipped disc irritating the L5 spinal nerve produces pain down the leg to the outside shin and big toe i.e. the normal territory in the leg supplied by the L5 spinal nerve. Spinal nerve root pain is also often associated with intense itching in the distribution of a particular dermatome. People often describe nerve pain is often described as lancinating, shooting, burning, and hypersensitive.
• Useful Medications - only partially sensitive to paracetamol, NSAIDs, Opioids. More sensitive to Anti-depressants, Anti-convulsants, Anti-arrhythmics, and NMDA Antagonists. Topical Capsaicin,  may be helpful.
• How do I find out if my pain is neuropathic? - try using the following Screening Tests.

• Source - due to possible over-activity sympathetic nervous system, and central / peripheral nervous system mechanisms. The sympathetic nervous system controls blood flow to tissues such as skin and muscle, sweating by the skin, and the speed and responsiveness of the peripheral nervous system. - see Sympathetic Pain.
• Causes - occurs more commonly after fractures and soft tissue injuries of the arms and legs, and these injuries may lead to Complex Regional Pain Syndrome (CRPS). CRPS was previously known as Reflex Sympathetic Dystrophy (RSD).
• Receptors activated - like nerve pain there are no specific pain receptors (non nociceptive). The same processes as mentioned above in Nerve Pain may operate in CRPS.
• Characteristics - presents as extreme hypersensitivity in the skin around the injury and also peripherally in the limb (allodynia), and is associated with abnormalities of sweating and temperature control in the area. The limb is usually so painful, that the sufferer refuses to use it, causing secondary problems after a period of time with muscle wasting, joint contractures, and osteoporosis of the bones. It is possible that the syndrome is initiated by trauma to small peripheral nerves close to the injury.
• Useful medications - many of the features of sympathetic pain are similar to those of nerve pain, and therefore nerve pain medications may be useful (Anti-depressants, Anti-convulsants, and Anti-arrhythmics). Drugs which lower blood pressure by causing vasodilatation (nifedipine) may also be useful when used in combination. Treatment should include appropriate multi-modal medications, sympathetic nerve blocks, and intensive rehabilitation combining occupational and physiotherapy.