Allodynia: Difference between revisions – Physiopedia


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== Overview ==

== Overview ==

Allodynia is defined by the International Association for the Study of Pain (IASP) as ”pain resulting from a stimulus that does not normally provoke pain”<ref>IASP. Terminology. Available from: https://www.iasp-pain.org/resources/terminology/ (accessed 12 Dec 2023)</ref>. For example, brushing a feather against the arm causes pain where it should only cause a sensation. Allodynia is categorised into three types:     

Allodynia is defined by the International Association for the Study of Pain (IASP) as

# ”’Dynamic”’ (or mechanical) when pain results from an object moving across the skin

 

 

 

# ”’Dynamic”’ (or mechanical) when pain results from an object moving across the skin

# ”’Thermal”’ which results from mild temperature changes

# ”’Thermal”’ which results from mild temperature changes

# ”’Tactile”’ (or static) which results from gentle touch or pressure.

# ”’Tactile”’ (or static) which results from gentle touch or pressure.

 

There is ultimately an error in the nerve communication network.

== Aetiology/Mechanism ==

== Aetiology/Mechanism ==

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There is an analogy of “crisscrossed” fibres, where the actual location of the crisscrossing can vary and may be located almost anywhere along the peripheral to the central nervous system tract. Allodynia can involve both the peripheral nervous system and central nervous system via sensitisation, and the mechanism behind the inappropriate pain sensations can evolve. This might partially explain the existing contradictory studies – they may all be measuring allodynia with neuronal confusion at different locations<ref name=”:0″>He Y, Kim PY. Allodynia [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2016 [cited 2022 Apr 9]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537129/</ref>.  The expression of allodynia may be as elegantly simple as a consistent increase in sympathetic nervous system activity, which leads to a sensitisation of C-fibres. The increase in C-fibre sensitisation is also a reflection of disinhibition of secondary spinal networks<ref>Kuner R. Central mechanisms of pathological pain. Nature medicine. 2010 Nov;16(11):1258-66. </ref>. In other words, a loss of spinal segregation of touch and pain can be a key mechanism of allodynia<ref>Kuner R, Flor H. Structural plasticity and reorganization in chronic pain. Nature Reviews Neuroscience. 2017 Jan;18(1):20-30. </ref>.   

There is an analogy of “crisscrossed” fibres, where the actual location of the crisscrossing can vary and may be located almost anywhere along the peripheral to the central nervous system tract. Allodynia can involve both the peripheral nervous system and central nervous system via sensitisation, and the mechanism behind the inappropriate pain sensations can evolve. This might partially explain the existing contradictory studies – they may all be measuring allodynia with neuronal confusion at different locations<ref name=”:0″>He Y, Kim PY. Allodynia [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2016 [cited 2022 Apr 9]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537129/</ref>.  The expression of allodynia may be as elegantly simple as a consistent increase in sympathetic nervous system activity, which leads to a sensitisation of C-fibres. The increase in C-fibre sensitisation is also a reflection of disinhibition of secondary spinal networks<ref>Kuner R. Central mechanisms of pathological pain. Nature medicine. 2010 Nov;16(11):1258-66. </ref>. In other words, a loss of spinal segregation of touch and pain can be a key mechanism of allodynia<ref>Kuner R, Flor H. Structural plasticity and reorganization in chronic pain. Nature Reviews Neuroscience. 2017 Jan;18(1):20-30. </ref>.   

Listed below are some of the most common diseases associated with allodynia:

Listed below are some of the most common diseases associated with allodynia:

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== Differential Diagnosis ==

== Differential Diagnosis ==

[[File: Allodynia.gif|thumb|Allodynia vs. Hyperalgesia ]]Another sensory condition that is often a differential diagnosis to allodynia is [[Pain Behaviours#sts=Hyperalgesia?utm source=physiopedia&utm medium=search&utm campaign=ongoing internal|hyperalgesia]]. Hyperalgesia is the condition of having increased sensitivity to pain or enhanced intensity of pain sensation<ref>Medical Definition of HYPERALGESIA [Internet]. www.merriam-webster.com. [cited 2022 Apr 9]. Available from: https://www.merriam-webster.com/medical/hyperalgesia</ref>. Patients do not necessarily perceive high pressure as pain, but the stimulus that would normally be perceived as low pain is sensed at a higher pain level. Patients respond to pain stimulus in the same way that they would if they did not have the condition, but it is an exaggerated response<ref name=”:0″ />.     

[[File: Allodynia.gif|thumb|Allodynia vs. Hyperalgesia ]]Another that is often a differential diagnosis to allodynia is [[Pain Behaviours#sts=Hyperalgesia?utm source=physiopedia&utm medium=search&utm campaign=ongoing internal|hyperalgesia]].

 

Hyperalgesia is the condition of having increased sensitivity to pain or enhanced intensity of pain sensation<ref>Medical Definition of HYPERALGESIA [Internet]. www.merriam-webster.com. [cited 2022 Apr 9]. Available from: https://www.merriam-webster.com/medical/hyperalgesia</ref>. pain stimulus that normally . an response<ref name=”:0″ />.     

==Treatment==

==Treatment==

There are multiple ways that healthcare providers can help treat allodynia. Providers can either treat the condition that is causing allodynia or try to reduce the pain.   

There are multiple ways that healthcare providers can help treat allodynia. Providers can either treat the condition that is causing allodynia or try to reduce the pain.   

This article or area is currently under construction and may only be partially complete. Please come back soon to see the finished work! (13/12/2023)

Allodynia is defined by the International Association for the Study of Pain (IASP) as

“Pain resulting from a stimulus that does not normally provoke/elicit pain”[1].

For example, brushing a feather against the arm causes pain where it should only cause a sensation. It is a clinical term to describe this phenomenon of altered quality of a sensation, and does not imply a mechanism or specific diagnosis.[1]It may however give insight into possible mechanisms at play.

Classification[edit | edit source]

Allodynia is categorised into three types:

  1. Dynamic (or mechanical) when pain results from an object moving across the skin (stroking)
  2. Thermal which results from mild temperature changes
  3. Tactile (or static) which results from gentle touch or pressure.

Allodynia is considered a sign/symptom, not a disease. It may be a patient’s chief complaint. Allodynia is the phenomenon of a non-painful stimulus producing a pain response, which implies an error in neuronal conduction. The mechanism behind this error is unclear. The strongest evidence that exists, thus far, suggests that sensory neuronal fibres may stimulate pain pathways, possibly due to an error in long-term potentiation. However, some studies suggest that superficial sensory components may also be involved. There is also evidence that different mental states can affect the perception of allodynia.

There is an analogy of “crisscrossed” fibres, where the actual location of the crisscrossing can vary and may be located almost anywhere along the peripheral to the central nervous system tract. Allodynia can involve both the peripheral nervous system and central nervous system via sensitisation, and the mechanism behind the inappropriate pain sensations can evolve. This might partially explain the existing contradictory studies – they may all be measuring allodynia with neuronal confusion at different locations[2]. The expression of allodynia may be as elegantly simple as a consistent increase in sympathetic nervous system activity, which leads to a sensitisation of C-fibres. The increase in C-fibre sensitisation is also a reflection of disinhibition of secondary spinal networks[3]. In other words, a loss of spinal segregation of touch and pain can be a key mechanism of allodynia[4].

Allodynia is often associated with conditions that involve sensitisation of the skin. Common examples include sunburn, inflammation or trauma.[1]Allodynia is a normal protective response after tissue injury has occurred and will usually subside as healing progresses. It may however increase over time in certain conditions, such as neuropathic pain conditions.[1]

Listed below are some of the most common diseases associated with allodynia:

Allodynia vs. Hyperalgesia

Another clinical term that is often a differential diagnosis to allodynia is hyperalgesia. Where allodynia refers to changes in the quality of sensation, hyperalgesia refers to changes in the intensity of the sensation of pain.[1]

Hyperalgesia is the condition of having increased sensitivity to pain or enhanced intensity of pain sensation[5]. There is an exaggerated experience of pain from a stimulus that is normally painful – i.e. an increased response/pain on suprathreshold stimulation (see image)[1] [2].

There are multiple ways that healthcare providers can help treat allodynia. Providers can either treat the condition that is causing allodynia or try to reduce the pain.

  • Medication: Anticonvulsants (used to treat seizures), triptans (used to treat migraines), and some antidepressants. Topical creams that can help manage allodynia will typically have lidocaine or capsaicin as the active ingredient.
  • Psychosocial interventions: Counselling may be recommended if signs of depression are detected. Biofeedback, mindfulness training, and cognitive behavioural therapy can change the way a person responds to pain.
  • Physiotherapy: The psychologically informed physiotherapist can include pain neuroscience education (PNE) and cognitive functional therapy. Physiotherapist can help manage allodynia with desensitization and/or mirror therapy.
  • Other procedures: A nerve block injection may be recommended to reduce pain in a specific nerve or nerve group.[6]

Allodynia can not be directly prevented, however, one can lower the risk of acquiring a condition that causes allodynia. Risk management includes exercising regularly, monitoring health, managing mental health , maintaining a healthy weight, having a balanced diet, and having good sleep hygiene.

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