Hyperalgesia

From Wikipedia, the free encyclopedia

Hyperalgesia Classification and external resources
ICD-9	782.0
DiseasesDB	30788
MeSH	D006930

Not to be confused with Hypoalgesia.

Hyperalgesia is an increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves.

[edit] Types

Hyperalgesia can be experienced in focal, discrete areas, or as a more diffuse, body-wide form. Conditioning studies have established that it is possible to experience a learned hyperalgesia of the latter, diffuse form. The focal form is typically associated with injury, and is divided into two subtypes:

Primary hyperalgesia describes pain sensitivity that occurs directly in the damaged tissues.
Secondary hyperalgesia describes pain sensitivity that occurs in surrounding undamaged tissues.

[edit] Causes

Hyperalgesia is induced by Platelet aggregating factor (PAF) which comes about in an inflammatory or an allergic response. This seems to occur via immune cells interacting with the peripheral nervous system and releasing pain-producing chemicals (cytokines and chemokines).^[1]

One unusual cause of focal hyperalgesia is platypus venom.

Long term opioid (e.g. heroin) users and those on opioid medications may experience hyperalgesia and experience pain out of proportion to physical findings.

Ikeda, Stark, Fischer, Wagner, Drdla, Jäger, et al. (2006) showed that stimulation of pain fibres in a pattern consistent with that from inflammation switched on a form of amplification in the spinal cord, long term potentiation.^[2] This occurred where the pain fibres contacted a pain pathway, the periaqueductal grey. Ikeda et al. argued that amplification in the spinal cord is another way of producing hyperalgesia.

[edit] References

Look up Hyperalgesia in
Wiktionary, the free dictionary.

^ Marchand, F., Perretti, M., & McMahon, S. B. (2005). Role of the immune system in chronic pain. Nature Reviews Neuroscience, 6, 521-532.
^ Ikeda, H., Stark, J., Fischer, H., Wagner, M., Drdla, R., Jäger, T., et al. (2006). Synaptic amplifier of inflammatory pain in the spinal dorsal horn. Science, 312, 1659-1662.

v • d • e Pain and nociception

Head and neck	Jaw and mouth pain (Odynophagia , temporal arteritis) • Ear pain (otalgia, otitis media, otitis externa) • Eye pain (glaucoma) • Head pain (headache, migraine, tension headache, cluster headache, cerebral aneurysm, sinusitis, meningitis) • Neck pain (atypical myocardial infarction)

Thorax	Back pain (upper back pain, lower back pain, spinal disc herniation, degenerative disc disease, coccydynia) • Breast pain (perimenstrual, breast cancer) • Chest pain (myocardial infarction, gastroesophageal reflux disease, pancreatitis, hiatus hernia, aortic dissection, asymptomatic pulmonary embolism, Tietze's syndrome) • Shoulder pain (right side - cholecystitis)

Abdominal pain	Left and right upper quadrant (peptic ulcer disease, gastroenteritis, hepatitis, pancreatitis, cholecystitis, atypical myocardial infarction, abdominal aortic aneurysm, asymptomatic gastric cancer) • Left and right lower quadrant (appendicitis, ulcerative colitis, Crohn's disease, ectopic pregnancy, endometriosis, pelvic inflammatory disease, diverticulitis, urolithiasis, pyelonephritis, colorectal cancer)

Limbs	Arms (myocardial infarction, left arm) • Legs (deep vein thrombosis, peripheral artery occlusive disease, claudication, spinal disc herniation, sciatica)

Joints	Small joints (osteoarthritis, rheumatoid arthritis, systemic lupus erythematosis, gout, pseudogout • Large joints (septic arthritis, hemarthrosis, osteonecrosis) • Back joints (ankylosing spondylitis, inflammatory bowel disease) • Other (psoriatic arthritis, Reiter's syndrome)

Musculoskeletal	Delayed onset muscle soreness, Myalgia, Physical trauma

Other/unspecified pain	Allodynia, breakthrough pain, chronic pain, congenital insensitivity to pain, congenital insensitivity to pain with anhidrosis, hyperalgesia, hyperpathia, neuralgia, pain asymbolia, pain disorder, paroxysmal extreme pain disorder, phantom pain, referred pain

Related concepts	Anterolateral system, gate control theory of pain, pain management (anesthesia, cordotomy), pain scale, pain threshold, posteromarginal nucleus, substance P