Wheal
From Wikipedia, the free encyclopedia
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|---|---|
| A welt (wheal) formed on a person's skin after being struck on the neck with a credit card | |
| ICD-10 | L50.9 |
| ICD-9 | 708 |
| DiseasesDB | 13606 |
| MedlinePlus | 000845 |
| eMedicine | med/3014 |
A wheal or wheal response (also termed a welt) is a firm, elevated, rounded or flat topped,[1], generally pale red papule or plaque[2] swellings of the skin. They are usually well demarcated[1] and may be round, oval, gyrate, annular[2] or irregular/serpiginous with pseudopods in shape. They often itch or have a burning sensation but are transient, typically disappearing within 24-48 hours.[2]
An itchy rash consisting of wheals may be called a uticarial exanthem, or urticaria, and more commonly as hives.
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[edit] Causes
Wheals are due to fluid build up in the skin as a result of a blow or lash to the skin as commonly occurs to paintball players, or an allergic reaction to innumerable initiating agents such as drugs or insect bites. These cause infiltration of edema into the papillary body of the dermis. Wheals may also be produced with Darier's sign, and by stroking the skin of certain normal persons who demonstrate the phenomenon called dermatographism.[3] Finally they may be formed by the injection of fluid with a hypodermic syringe.
While the borders are sharp, they are not stable, and as this short-lived papillary edema shifts, each wheal transiently moves[4] from involved to adjacent uninvolved areas over a period of hours. Also note, while this finding is usually pale red, if the amount of edema is adequate to compresses superficial vessels, the wheal may have a white center.[3] The epidermis is not affected and there is no scaling.[3]
[edit] Pathophysiology
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This section does not cite any references or sources. (March 2008) Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed. |
This effect is most likely mediated by Neurokinin 1 activation in response to substance P released during the injury by cutaneous sensory nerve fibers A & C. The result of NK1 activation is plasma leakage, and arteriole dilation, which increases blood flow.
[edit] See also
[edit] Footnotes
- ^ a b (2004) in Lee Goldman, Lee; Ausiello, Dennis: Cecil textbook of medicine, 22nd ed., Philadelphia: W.B. Saunders, 2451. ISBN 0-7216-9652-X.
- ^ a b c (2001) in Braunwald, Eugene; Fauci, Anthony; Kasper, Dennis; Hauser, Stephen; Longo, Dan; Jameson, Larry: Harrison's principles of internal medicine, 15th Edition, New York: McGraw-Hill, 95 & 306. ISBN 0070072728.
- ^ a b c (1986) in Fitzpatrick, Thomas B. ed.: Dermatology in general medicine: textbook and atlas. New York: McGraw-Hill, 29-30. ISBN 0070796890.
- ^ Habif, Thomas P. (2004). Clinical dermatology: a color guide to diagnosis and therapy. St. Louis: Mosby, 825. ISBN 0-323-01319-8.
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