itch - REVIEW Review Itch Gil Yosipovitch, Malcolm W...

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For personal use. Only reproduce with permission from The Lancet Publishing Group. REVIEW 690 THE LANCET • Vol 361 • February 22, 2003 • www.thelancet.com Itch, along with pain, is a major part of nociception and an important symptom of systemic problems, as well as skin diseases. Progress in understanding of its neuropathophysiology and molecular basis has been hampered by absence of specific and sensitive investigational methodology in man, and unsuitability of animal models. Since the last update in The Lancet more than 5 years ago on itch pathophysiology, 1 research has begun to overcome these difficulties, with important clinical implications. Definitions, types, and clinical classification Itch has many similarities to pain. 2 Both are unpleasant sensory experiences, but the behavioural response patterns differ—pain elicits a reflex withdrawal, whereas itch leads to a scratch reflex. However, both can lead to serious impairment of quality of life. A stimulus causing itch leads to two distinct responses: 3 first, a well localised itch at the site of the stimulus, which persists only briefly after the stimulus has been removed; and second, a subsequent diffuse poorly localised area surrounding the site, which responds with intense itch when exposed to gentle touch or other minor stimuli. This sensation of itchy skin is also called alloknesis. Twycross 4 has proposed a clinical classification of four categories of itch, on the basis of advances in understanding of the peripheral and central origins of itch. Pruritoceptive itch Itch originating in the skin, due to inflammation, dryness, or other skin damage, is termed pruritoceptive and is transmitted by C nerve fibres. Examples are itch due to scabies, urticaria, and reactions to insect bite. Lancet 2003; 361: 690–94 Department of Dermatology, Wake Forest University, Winston Salem, North Carolina, USA (Prof G Yosipovitch MD) ; Department of Dermatology, Faculty of Medicine, Hospital University Kebangsaan Malaysia, Kuala Lumpur, Malaysia (Prof M W Greaves FRCP) ; and Department of Anaesthesiology, Mannheim University, Heidelberg, Germany (M Schmelz MD) Correspondence to: Prof Gil Yosipovitch, Department of Dermatology, Wake Forest University, Medical Center Boulevard, Winston Salem, NC 27517, USA (e-mail: gyosipov@wfubmc.edu) Neuropathic itch Itch that arises because of disease located at any point along the afferent pathway is called neuropathic itch. 5 Post-herpes zoster neuropathy and the itch occasionally associated with multiple sclerosis and brain tumours are in this category. Neurogenic itch Neurogenic itch is defined as that which originates centrally but without evidence of neural pathology, such as the itch of cholestasis, which is due to the action of opioid neuropeptides on µ-opioid receptors.
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This note was uploaded on 10/14/2010 for the course ZOO 4125 taught by Professor Flanigan during the Fall '10 term at Wyoming.

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itch - REVIEW Review Itch Gil Yosipovitch, Malcolm W...

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