Chronic Itch

Chronic Itch

Subject – Science and Tech

Context – The elderly are prone to chronic conditions that manifest as itches

Concept –

• Chronic itch can be dermatologic-often triggered by the release of histamine, and treated with antihistamine drugs (e.g., Benadryl), neuropathic (related to the nervous system, as in shingles, nerve compression and cerebral hemorrhage), or systemic (as in renal insufficiency) or psychogenic (as in obsessive-compulsive disorders).
• The elderly are particularly prone to chronic conditions that manifest as itches.
• Associated causes could be diabetes, hypothyroidism, several cancers and Iron deficiency.
• Factors that induce itch are called pruritogens. Tissues that are sensitive to itch include the skin, mucus membranes and the cornea of the eye.
• Some nerve fibres in these tissues (pruriceptors) are stimulated by pruritogens and the resulting signals are carried, via itch-signaling neurons in the spinal cord, to the brain. There are several different receptors and channels that respond to pruritogens. A great degree of redundancy in their roles ensures that no matter what, the itch sensation gets through to your brain. A common example of chronic itch is atopic dermatitis, an inflammatory condition showing cracked, itchy skin, which is often caused by allergens.
• The scratch response is a key difference between itch and pain. Sudden, sharp pain causes you to hurriedly retract and thus escape damage; scratching actually draws attention to the cause of the itch. Scratching evokes an inhibition of itch-signaling neurons in the spinal cord. This reduces the quantum of itch sensations that reach the brain. But the respite is only short-lived – by scratching, you are inflicting mild pain, and in your brain, pain can momentarily overshadow the itch sensation.
• Scratching may even trigger reward systems in the brain, making it a pleasurable feeling. But for patients with chronic itch, scratching can be a bane, causing damage to the skin and aggravating the itch.
• In a series of deceptively simple experiments, the neuroscientist, showed that people who have recently lost a limb in accidents and often complain of their ‘phantom hand itching like crazy’, could obtain relief by scratching various parts of their face – scratch the upper lip, and the absent index finger feels comforted, and so on.
• Novel therapeutic methods try to tackle chronic itch at many different points, from the skin to the central nervous system. UVB light is known to attenuate histamine release from immune cells in the skin, so phototherapy has proved useful. Garments of a silk that is coated with antimicrobial compounds are another strategy to soothe itching skin. Long-term itch leads to functional anomalies in the regions of the brain associated with itch, and non-invasive transcranial direct-current simulation has been shown to offer relief.