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lichen

 [li´ken]
1. any of certain plants formed by the mutualistic combination of an alga and a fungus.
2. any of various papular skin diseases in which the lesions are typically small, firm papules set very close together.
lichen amyloido´sus a condition characterized by localized cutaneous amyloidosis.
lichen fibromucinoido´sus (lichen myxedemato´sus) a condition resembling myxedema but unassociated with hypothyroidism, marked by mucinosis and a widespread eruption of asymptomatic, soft, pale red or yellowish, discrete papules.
lichen ni´tidus a usually asymptomatic chronic inflammatory eruption consisting of numerous glistening, flat-topped, discrete, smooth, commonly skin-colored micropapules, located most often on the penis, lower abdomen, inner thighs, flexor aspects of the wrists and forearms, breasts, and buttocks. Widespread involvement may produce confluence of the lesions, with formation of scaly plaques.
lichen pila´ris lichen spinulosus.
lichen planopila´ris a variant of lichen planus characterized by formation of cone-shaped horny papules around the hair follicles, in addition to the typical lesions of ordinary lichen planus.
lichen pla´nus an inflammatory skin disease with wide, flat, purplish, shiny papules in circumscribed patches; it may involve the hair follicles, nails, and buccal mucosa; called also lichen ruber planus.
lichen ru´ber monilifor´mis a generalized or localized eruption with either round, dome-shaped, waxy, dark or bright red papules, or waxy, yellow, milia-like papules, often forming a moniliform (string-of-beads) pattern, sometimes arranged in keloidal bands. Some authorities consider the condition to be a variant of lichen simplex chronicus.
lichen ru´ber pla´nus lichen planus.
lichen sclero´sus (lichen sclero´sus et atro´phicus) a chronic atrophic skin disease marked by white papules with an erythematous halo and keratotic plugging. It sometimes affects the vulva (kraurosis vulvae) or penis (balanitis xerotica obliterans).
lichen scrofuloso´rum (lichen scrofulo´sus) a form of tuberculid manifested as an eruption of clusters of lichenoid papules on the trunk of children with tuberculous disease.
lichen sim´plex chro´nicus dermatosis of psychogenic origin, marked by a pruritic discrete, or more often, confluent lichenoid papular eruption, usually confined to a localized area. Mechanical trauma, such as scratching or rubbing the area, is a factor in its development. The lesions may arise from normal skin or they may occur as a complication of other forms of dermatitis. Called also circumscribed or localized neurodermatitis and lichen chronicum simplex.

Treatment consists of administration of corticosteroids applied locally as a cream or given by intralesional injection to relieve the pruritus. The area should be protected by light dressings and the patient encouraged to avoid mental stress, emotional upsets, and irritation of the affected area. The application of very hot or very cold compresses may afford temporary relief of the itching. The condition tends to become chronic with unexplained remissions and reappearance of lesions in a different part of the body.
lichen spinulo´sus a condition in which there is a horn or spine in the center of each hair follicle; called also lichen pilaris.
lichen stria´tus a self-limited condition characterized by a linear lichenoid eruption, usually in children.
lichen urtica´tus papular urticaria.

li·chen

(lī'ken),
A discrete flat papule or an aggregate of papules giving a patterned configuration resembling lichen growing on rocks.
[G. leichēn, lichen; a lichenlike eruption]

lichen

/li·chen/ (līk´'n)
1. any of certain plants formed by the mutualistic combination of an alga and a fungus.
2. any of various papular skin diseases in which the lesions are typically small, firm papules set close together.

lichen amyloido´sus  a condition characterized by localized cutaneous amyloidosis.
lichen fibromucinoido´sus , lichen myxedemato´sus a condition resembling myxedema but unassociated with hypothyroidism, marked by a fibrocystic proliferation, increased deposition of acid mucopolysaccharides in the skin, and the presence of a circulating paraprotein; it may present as lichenoid papules or urticaria-like plaques and nodules.
lichen ni´tidus  a chronic inflammatory eruption consisting of many, pinhead-sized pale, flat, sharply marginated, glistening, discrete papules, scarcely raised above the skin level.
lichen planopila´ris  a variant of lichen planus characterized by formation of acuminate horny papules around the hair follicles, in addition to the typical lesions of ordinary lichen planus.
lichen pla´nus  an inflammatory skin disease with wide, flat, violaceous, shiny papules in circumscribed patches; it may involve the hair follicles, nails, and buccal mucosa.
lichen ru´ber monilifor´mis  a variant of lichen simplex chronicus with papules arranged in linear beaded bands.
lichen ru´ber pla´nus  l. planus.
lichen sclero´sus  a chronic atrophic skin disease marked by white papules with an erythematous halo and keratotic plugging, usually around the external genitalia or in the perianal region.
lichen scrofuloso´rum , lichen scrofulo´sus any eruption of minute reddish lichenoid follicular papules in children and young adults with tuberculosis.
lichen sim´plex chro´nicus  a dermatosis of psychogenic origin, marked by a pruritic discrete or, more often, confluent papular eruption, usually confined to a localized area.
lichen spinulo´sus  a condition in which there is a horn or spine in the center of each hair follicle.
lichen stria´tus  a self-limited condition characterized by a linear lichenoid eruption, usually in children.

lichen

(lī′kən)
n.
1. A composite organism made up of a fungus, usually an ascomycete, that grows symbiotically with an alga or a cyanobacterium and characteristically forms a crustlike or branching growth on rocks or tree trunks.
2. Medicine Any of various skin diseases characterized by patchy eruptions of small, firm papules.
tr.v. li·chened, li·chening, li·chens
To cover with lichens.

li′chen·ous adj.

li·chen

(lī'kĕn)
A discrete flat papule or an aggregate of papules giving a patterned configuration resembling lichens growing on rocks.
[G. leichēn, lichen; a lichenlike eruption]

lichen

(li'ken) [Gr. leichen, lichen]
1. Any form of papular skin disease, esp. lichen planus.
2. In botany, any of numerous plants consisting of a fungus growing symbiotically with algae. They form characteristic scaly or branching growths on rocks or barks of trees.

myxedematous lichen

Generalized eruption of asymptomatic nodules caused by mucinous deposits in the upper layers of the skin and in vessels and organs.

lichen nitidus

A rare skin condition characterized by small, chronic, asymptomatic papules that are usually pink and are usually located only on the penis, abdomen, and flexor surfaces of the elbows and palms.

lichen pilaris

Keratosis pilaris.

lichen planopilaris

A follicular papulosquamous eruption, typically found on the scalp, and often associated with lichen planus.
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LICHEN PLANUS
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LICHEN PLANUS

lichen planus

An inflammatory rash marked by the presence of itchy, red to violet, polygon-shaped papules, which typically appear on the scalp, in the oral cavity, or on the limbs. The papules may merge into plaques crisscrossed by Wickham striae. Typically, the rash persists for 1 to 2 years and then spontaneously improves although about one in five patients will suffer a recurrence. Synonym: lichen ruber planus See: illustration

Etiology

The cause of the rash is unknown, but it is occasionally associated with the use of chemicals (such as photoprocessing compounds, gold) or medications (such as beta blockers, diuretics, nonsteroidal anti-inflammatory drugs).

Treatment

Corticosteroids, applied topically, taken orally, or injected into the lesions, are often effective.

illustration

lichen ruber moniliformis

Large verrucous lesions of lichen planus arranged like beads in a necklace.

lichen ruber planus

Lichen planus.
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LICHEN SCLEROSUS ET ATROPHICUS

lichen sclerosus et atrophicus

A chronic atrophic skin disorder marked by the appearance of discrete, flat-topped, white papules, which may coalesce and degenerate. The skin affected by the rash, which occurs most often on the vulva, is often thin, shiny, and scarred. Although this condition is not considered precancerous, squamous cell carcinomas arise in 1% to 5% of cases. See: illustration

Symptoms

Itching of the vulva, which may be intractable, is the most common complaint.

Treatment

Potent topical corticosteroids produce remission, but not cure, in the great majority of patients.

Synonym: vulvar dystrophy; vulvar pruritus

lichen scrofulosus

An eruption of tiny punctate reddish-brown papules arranged in circles or groups in young people with tuberculosis. The lesions are caused by the spread of the tubercle bacilli through the blood to the skin.
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LICHEN SIMPLEX CHRONICUS

lichen simplex chronicus

An itching papular eruption that is circumscribed and located on skin that has become thickened and pigmented as a result of scratching. Synonym: circumscribed neurodermatitis See: neurodermatitis for illus.
illustration

lichen spinulosus

Keratosis pilaris.

lichen striatus

A papular eruption usually seen on one extremity of a child. It is arranged in linear groups and consists of pink papules. The disease, though self-limiting, may last for a year or longer.

tropical lichen

Prickly heat.

lichen tropicus

Prickly heat.

lichen

Any skin eruption.

lichen

a composite organism formed by the symbiotic association (see SYMBIOSIS of a green alga or a CYANOBACTERIUM and a fungus, usually from the ASCOMYCOTA or BASIDIOMYCOTA. The fungus makes up 80–90% of the association. The fungus gains oxygen and carbohydrates from the alga or cyanobacterium. The alga or cyanobacterium gains water, CO2 and mineral salts from the fungus and is protected from desiccation. Lichens reproduce vegetatively by means of soredia (hyphal cells enclosing algal or cyanobacterial cells) and sexually by means of the fungal apothecia or PERITHECIA. However, where no algae or cyanobacteria of the usual association occur, the germinating fungal spore dies. Lichens are very common on trees and rocks in unpolluted areas and can be used as an INDICATOR SPECIES.

lichen

1. any of certain plants formed by the mutualistic combination of an alga and a fungus.
2. any of various papular skin diseases in which the lesions are typically small, firm papules set very close together, the specific kind being indicated by a modifying term.

lichen tropicus
see equine allergic dermatitis.
References in periodicals archive ?
Manual mowing lichens with rare soft slopes and areas inaccessible to lawnmowers,
Sam Bosanquet, moss and lichen ecologist from Natural Resources Wales (NRW), said: "The discovery of these new species is a significant find, and highlights the importance of this area of woodland as a rich habitat, home to a diverse range of plants, lichens and mosses.
Dave Lamacraft, Plantlife plants and fungi officer for Wales, and three other experts surveyed an area of woodland equivalent in size to 1,000 football pitches, and made important discoveries including: a type of barnacle lichen never before recorded in Wales and found down a near-inaccessible ravine; a species of felt lichen that was last seen in the 1800s, and a species of tree flute, thought to be extinct in England and Wales.
In the 1980s, Algerian and foreign researchers began studying lichenology, although, aside from the study of the use of lichens as bioindicators of atmospheric pollution [24, 25, 26, 27], a comprehensive survey of epiphytic lichens had yet to be published.
The lichens appear to be essential for the reproductive success of Dudleya verityi," says Elvin.
Lichen: a Beauty Exposed, will run in the main gallery and foyer of the town's Queen's Hall from October 18 until November 22, marking the culmination of Hexham-based Iain's project which has seen him photograph rich collections of lichens on the central section of Hadrian's Wall as well as in the immediate vicinity of the world heritage site: along the Hadrian's Wall Corridor which extends 10 miles to the north and south.
One foliose lichen and two moss samples were collected from trees at Drake's Seat on Saint Thomas (18[degrees]21'41" N, 64[degrees]57'04"W; 262 m elevation).
He also noticed that nodules throughout the rock looked strikingly similar to the rootlike structures put out by primitive lichen or fungi found in other ancient soils.
In 1967 the National Science Foundation awarded him the Antarctic Medal for his work on lichens at McMurdo station in Antarctica and announced that a peak in the Queen Alexandria Range of the Transantarctic Montains, Antarctic had been named "Ahmadjian Peak" in his honor.
Portuguese ecologist Godinho explains how lichens can be used to monitor both ephemeral changes in air pollution and its accumulation over time.
The organism, renowned for its medicinal qualities, is one of ten endangered species of native lichens, beetles, bees, jellyfish and shrimps now enjoying new titles after previously only being listed in Latin.