Allodynia
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Allodynia, meaning "other pain", is an exaggerated response to otherwise non-noxious stimuli and can be either static or mechanical. Allodynia is not referred pain, but can occur in other areas than the one stimulated; it is also dysesthetic.
For example, a person with allodynia may perceive light pressure or the movement of clothes over the skin as painful, whereas a healthy individual will not feel pain.
Pathophysiology
One explanation of the mechanism for allodynia is that the associated nerve damage results in decreased firing thresholds of nociceptive fibres.
Alternatively, it has been postulated that peripheral nerve injury could induce collateral sprouting of non-nociceptive primary afferent neurones, such as A-beta low threshold mechanoreceptors, into the superficial (nociceptive) laminae in the dorsal horn of the spinal cord. These collateral branches could form functional contacts with nociceptive second order neurones, normally innervated by C-fibre nociceptive primary afferent neurones and transmit an innocous input as noxious.
Associated disturbances
Allodynia is a clinical feature of pain conditions such as migraine, postherpetic neuralgia, fibromyalgia, and neuropathies.
Types
There are different kinds or types of allodynia:
- Mechanical allodynia (also known as tactile allodynia) - Pain from light touch/pressure applied to the skin in the area of the damaged nerve. Mechanical allodynia can be dynamic or static. Also it has been shown that lowering barometric pressure aggravates mechanical allodynia in a rat model of neuropathic pain
- Thermal (heat or cold) allodynia - Pain from normally mild skin temperatures in the affected area.
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