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Do you know why Allodynia turns a harmless touch into excruciating pain?
In our daily lives, we often encounter a variety of minor discomforts, but some people may experience severe pain from these harmless touches. This is a condition called "allodynia", which can turn stimuli that are not usually painful into excruciating pain. For example, sunburned skin may experience intense discomfort when it touches clothing or takes a shower, irritants that are otherwise completely harmless.
Types of AllodyniaAllodynia gets its name from the Ancient Greek words "állos" meaning "other" and "odúnē" meaning "pain."
Allodynia can be divided into several different types:
- Mechanical Allodynia (Tactile Allodynia): Pain when lightly touched.
- Static Mechanical Allodynia: Painful response to touch.
- Dynamic Mechanical Allodynia: Pain when gently touched.
- Hot/Cold Allodynia: Pain caused by changes in normal skin temperature.
- Motor Allodynia: Pain triggered by normal movement of a joint or muscle.
Causes
Allodynia is a clinical feature of many painful conditions, including neuropathy, complex regional pain syndrome, postherpetic neuralgia, fibromyalgia, and migraine. Some stem cell treatments for nerve damage may also cause allodynia.
PathophysiologyCellular Level
At the cellular level, mechanoreceptors can influence the output of pain neurons through connections with the same class of corpus callosum neurons. Activation of these neurons can reduce or eliminate pain perception. Fibers descending from the brain can block the transmission of pain signals via various internal inhibitory neurons. Changes in these mechanisms are thought to be involved in the pathology of Allodynia.
Molecular level
At the molecular level, the hypersensitivity response causes neurons to become more responsive to repeated stimulation. Some studies have pointed to chemicals on specific pathways in the spinal cord and thalamus that contribute to this increased allergy, including the involvement of the CCL21 protein and tumor necrosis factor (TNF-alph).
TreatmentA sensitized central nervous system is thought to play an important role in the emergence of allodynia.
There are currently many drugs available for the treatment of allodynia, and different types of allodynia may require different drugs. Includes:
- Dynamic Mechanical Allodynia: such as pentoxynilamine, lidocaine, opioids, etc.
- Static Mechanical Allodynia: Mainly based on sodium channel blocking drugs, such as gabapentin and progesterone.
- Cold Allodynia: such as Lamotrigine, Lidocaine, etc.
Famous Cases
Howard Hughes is thought to have suffered from allodynia in his later years, which resulted in him rarely bathing, dressing or cutting his nails, and these normal daily activities could cause him severe pain.
In summary, allodynia is a complex and distressing pathological condition for patients. As our understanding of this disease deepens, perhaps we will be able to provide patients with more effective treatments in the future. So why can harmless touch in normal, everyday life trigger such intense feelings of pain?
