Itch (also known as pruritus ) is a sensation that causes the desire or reflex to scratch. Itch has rejected many attempts to classify it as one type of sensory experience. Modern science has shown that itching has a lot in common with pain, and while both are an unpleasant sensory experience, their behavioral response patterns are different. Pain creates a withdrawal reflex, whereas itching causes initial reflexes.
Nerve fibers that are not bermyelin for itching and pain come from the skin; However, the information for them is delivered centrally in two different systems that both use the same neural beam and the spinotalamic channel.
Video Itch
Signs and symptoms
Pain and itching have very different behavioral response patterns. Pain generates a withdrawal reflex, which leads to retraction and therefore the reaction seeks to protect the endangered body parts. Itching in contrast creates an initial reflex, which pulls one into the affected skin sites. Itching produces foreign body stimuli below or on the skin and also the urge to remove them. For example, responding to a local itch sensation is an effective way to remove insects from one's skin.
Scratching is traditionally regarded as a way to relieve yourself by reducing the itching sensation that is distracting. However, there is a hedonistic aspect of the scratches, because people will find a very nice dangerous scratch. This can cause problems with chronic itching patients, such as those with atopic dermatitis, who may scratch the affected areas until they no longer produce a pleasant or painful sensation, rather than when the itching sensation disappears. It has been hypothesized that aspects of scratching motivation include the frontal brain area of ​​appreciation and decision making. These aspects may contribute to the compulsive nature of itching and scratching.
infectious itch
The "infectious itchy" event is a very common occurrence. Even discussions about the subject of itching can give one a desire to scratch. Itching may be more of a local phenomenon where we scratch. The results of the study show that itching and scratching are caused purely by visual stimuli in general lectures on itching. Pain sensation can also be induced in the same way, often by listening to the description of the injury, or seeing the injury itself.
There is little detailed data on central activation for itching is contagious, but it is hypothesized that the human mirror neuron system exists where we mimic certain motor actions when we see others performing the same actions. A similar phenomenon in which mirror neurons are used to explain the cause is infectious yawning.
Inhibition of itching pain
The itching sensation can be reduced by many painful sensations. Studies conducted in the last decade have shown that itching can be inhibited by many other forms of painful stimuli, such as dangerous heat, physical/scratching friction, harmful chemicals, and electric shock.
Maps Itch
Cause
Infection
- Allergic reactions to contact with certain chemicals, such as urushiol, derived from poison ivy or poison oak, or Balsam Peru, are found in many foods and fragrances. Certain allergens can be diagnosed in patch test.
- Body lice, found under subsistence conditions
- Cutaneous larva migraine, skin disease
- Head lice, if limited to neck and scalp
- Herpes, viral disease
- Insect bites, such as mosquito bites or chiggers
- Photodermatitis - sunlight reacts with chemicals in the skin, leading to the formation of irritant metabolites
- Pubic lice, if limited to genital area
- Scabies, especially when some other close contacts are also itchy
- Shave, which can irritate skin
- Itching in swimmers, short-term immune reactions
- Varicella - chicken pox, is common among children and is highly contagious
Environment and allergies
- Foreign body on the skin is the most common cause of non-pathological itching.
- Urticaria (also called itching) usually causes itching
Skin disorders
- Dandruff - an enormous amount of flakes associated with this sensation
- Keratoderma palmoplantar collision, a group of disorders characterized by abnormal thickening of the palms and soles of the feet
- Skin conditions (such as psoriasis, eczema, sunburn, athlete's feet, and hidradenitis suppurativa). Most are inflammatory.
- Healing of scabs, scarring, and the development or appearance of moles, acne, and hair that grows inward from beneath the epidermis
- Xerosis - dry skin, the most common cause, often seen in winter and also associated with older age, frequent bathing in hot showers or showers, and high temperature and low humidity environments
Medical disorders
- Diabetes mellitus, a group of metabolic diseases in which a person has high blood sugar
- Hyperparathyroidism, excessive parathyroid gland activity leading to overproduction of parathyroid hormone (PTH)
- Iron deficiency anemia, general anemia (low red blood cells or hemoglobin levels)
- Jaundice and cholestasis - bilirubin is a skin irritation at high concentrations
- Malignancy or internal cancer, such as lymphoma or Hodgkin's disease
- Polycythemia, which can cause general itch due to increased histamine
- Psychiatric illness ("psychogenic itching," as can be seen in delusional parasitosis)
- Thyroid disease
- Uraemia - the itching sensation of this cause is known as uremic pruritus
Drugs
- Drugs (such as opioids) that activate histamine receptors (H1) or trigger histamine release
- Chloroquine, a drug used in the treatment and prevention of malaria
Associated with pregnancy
- pregnancy pemphigoid, pregnancy dermatosis
- Intrahepatic cholestasis of pregnancy, a medical condition in which cholestasis occurs
- pruritus urticaria and pregnancy plaque (PUPPP), a chronic itchy rash
More
- Menopause, or changes in hormonal balance associated with aging
Mechanism
Itching can come from the peripheral nervous system (dermal or neuropathic) or in the central nervous system (neuropathic, neurogenic, or psychogenic).
Dermal/pruritoceptive
Skin itching is known as pruritoceptive , and can be induced by various stimuli, including mechanical, chemical, thermal, and electrical stimuli. The main afferent neurons responsible for histamine-induced itching are non-bermyelin-C fibers.
Two main classes of human C-fiber nociceptors exist: responsive nociceptors of mechano and nociceptors that are insensitive to mechano. Mechano-responsive nociceptors have been shown in studies to respond to most pain, and receptors that are insensitive to mechano respond mostly to the itch caused by histamine. However, it does not explain the itch caused by the machine or when the itch is produced without a flare reaction that does not involve histamine. Therefore, it is possible that pruritoceptive neural fibers have different fiber classes, which is unclear in the current study.
Studies have been done to show that itchy receptors are found only in the top two skin layers, epidermis and epidermal/dermal transition layers. Shelley and Arthur have verified the depth by injecting the itching powder spicula (Mucuna pruriens), and found that maximum sensitivity was found in the deepest layer of basal cells or epidermal layers. The surgical removal of the skin layer eliminates the patient's ability to feel itchy. Itching is never felt in muscles or joints, which strongly suggests that the deep tissues may not contain an itching signal.
The sensitivity to pruritic stimulation is spread evenly throughout the skin, and has a clear dot distribution with equal density of pain. Different substances that cause itching in intracutaneous injection (injection in the skin) only cause pain when injected subcutaneously (under the skin).
Itching is immediately eliminated in skin areas treated with excitotoxin capsaicin nociceptor, but remains unchanged in areas of skin that are not sensitive to touch with pretreatment with saponins, anti-inflammatory agents. Although experimental induced itching can still be felt under the complete A-fiber conduction block, it is significantly reduced. Overall, the itching sensation is mediated by A-delta and C nociceptors located in the uppermost layer of the skin.
Neuropathic
Neuropathic itching can come from any point along the afferent pathway as a result of damage to the nervous system. They may include diseases or disorders in the central nervous system or peripheral nervous system. Examples of neuropathic itching are initially notalgia paresthetica, brachioradial pruritus, brain tumor, multiple sclerosis, peripheral neuropathy, and nerve irritation.
Neurogenic
Neurogenic itching, which is centrally induced but without nerve damage, is largely associated with increased accumulation of exogenous opioids and synthetic opioids.
Psychogenic
Itching is also associated with some psychiatric symptoms such as tactile hallucinations, delusions of parasitosis, or obsessive-compulsive disorder (such as OCD-related neurotic scratches).
Peripheral sensitization
Inflammatory mediators - such as bradykinin, serotonin (5-HT) and prostaglandin - are released during painful inflammatory conditions or pruritus not only activates pruriceptors but also causes acute nociceptors sensitization. In addition, expression of nerve growth factor (NGF) may cause structural changes in nociceptors, such as growth. NGF is high in injured or inflamed tissue. Increased NGF is also found in atopic dermatitis, hereditary and non-infectious skin diseases with chronic inflammation. NGF is known to regulate neuropeptides, especially substance P. Substance P has been found to have an important role in inducing pain; however, there is no confirmation that the P substances directly cause acute sensitization. In contrast, P substance may contribute to itching by increasing neuronal sensitization and may affect the release of mast cells, which contain many rich histamine granules, during long-term interactions.
Central sensitization
Malicious input to the spinal cord is known to produce central sensitization, which consists of allodynia, excessive pain, and emphasizes hyperalgesia, extreme sensitivity to pain. Two types of mechanical hyperalgesia may occur: 1) a usually painless touch around an injured wound or tear can trigger a painful sensation (touching hyperalgesia), and 2) a slightly painful puncture stimulation is considered more painful around the inflammatory focal area (punctuate hyperalgesia). Tread-induced hypergesgesia requires continuous shooting of primary afferent nociceptors, and punctuate hyperalgesia does not require continuous firing which means it can last for hours after trauma and can be stronger than it is usually experienced. In addition, it was found that patients with neuropathic pain, histamine ionophoresis produce a burning sensation rather than itching, which would be induced in normal healthy patients. This suggests that there is spinal hypersensitivity to the C-fiber input in chronic pain.
Treatment
A variety of over-the-counter anti-itch medications and prescriptions are available. Some plant products have proven effective anti-pruritus, others do not. Non-chemical drugs include cooling, heating, soft stimulation.
Topical antipruritics in the form of creams and sprays are often available without a prescription. Oral itching drugs also exist and are usually prescription drugs. The active ingredients usually include the following classes:
- Antihistamines, such as diphenhydramine (Benadryl)
- Corticosteroids, such as topical hydrocortisone creams; see topical steroids
- Counterirritants, such as mint oil, menthol, or camphor
- Crotamiton (trade name Eurax) is an antipruritic agent available as a cream or lotion, often used to treat scabies. The mechanism of action is still unknown.
- Local anesthetics, such as topical benzocaine (Lanacane) cream
Phototherapy is useful for severe itching, especially if caused by renal failure. The common type of light used is UVB.
Sometimes scratches alleviate the isolated itch, so that the presence of a device such as a rear scratcher. Often, however, scratching may increase the itchiness and even cause further damage to the skin, dubbed "cycle of itching-itching."
The therapeutic refinement for dry skin is to maintain adequate skin moisture and topical emollients.
History
In 1660, German physician Samuel Hafenreffer defined the itch.
Diagnosis
Epidemiology
About 280 million people worldwide, 4% of the population, have difficulty with itching. This is comparable to 2-3% of the population with psoriasis.
See also
- Formations, sensations that resemble small insects crawling above or below the skin
- Pruritus ani (also known as anusitis), skin irritation at the rectum exit (anus), causes the desire to scratch
- It feels itchy, a phenomenon in which a stimulus is applied in one region of the body perceived as itching or irritation in different parts of the body
References
Further reading
-
Han, Liang; Dong, Xinzhong (May 6, 2014). "Itching Mechanism and Circuit". Annual Biophysical Review . 43 (1): 331-355. doi: 10.1146/annurev-biophys-051013-022826. PMCÃ, 4081479 - Andrew D, Craig AD (2001). "My lamina neurotalamic lamina selective neurons are sensitive to histamine: central nerve pathways for itching". Nat. Neurosci . 4 (1): 72-7. doi: 10.1038/82924. PMID 11135647.
- National Cancer Institute (2003) "Pruritus" Obtained August 22, 2005.
External links
Source of the article : Wikipedia
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