Skin Plaque Appearance, Causes, and Diagnosis

Skin plaques are elevated, solid, superficial lesions that are typically more than 1 centimeter (a little more than half an inch) in diameter. These lesions are associated with a number of skin conditions, most commonly psoriasis.

The word plaque is French for "plate," which is fitting because skin plaques often look like miniature (dirty) dishes.

This article discusses different types of skin plaques and the conditions that cause them. It also explains how to care for and treat affected skin.

Skin Plaque Appearance and Symptoms

A skin plaque can be flat or appear as a thickened area of the skin that isn't visibly elevated above the surface of the skin.

Skin plaques can have defined borders or not, and they can take on many different shapes, including:

• Annular (ring-shaped)
• Arcuate (half-moon-shaped)
• Polygonal (varied and not geometric)
• Polymorphic (varied shapes)
• Serpiginous (snake-shaped)
• Poikilodermatous (variegated)

Plaques can appear anywhere on the body, but they most often appear on the elbows, knees, scalp and lower back.

The amount of skin affected by plaques varies. Sometimes plaques on the skin are a few small spots that look similar to dandruff; other times they are huge eruptions that cover larger parts of the body, like the forearms.

The symptoms associated with plaques vary depending upon the skin condition present (see below.) Generally, however, there are a few symptoms associated with plaques related to any condition:

• Itching and burning
• Soreness (often a deep, nonspecific achy feeling)
• Swelling and stiffness on joints where plaques are located

What Causes Plaques on Skin?

There are likely several different mechanisms behind the formation of plaques, though plaque psoriasis has been studied most extensively.

Although the exact cause of psoriasis is unknown, it's thought to be associated with the immune system and a type of white blood cell: the T lymphocyte, or T cell.

T cells are constantly working to fend off viruses and bacteria, but for those with psoriasis, T cells are overactive and accidentally fight off healthy skin cells.

In turn, there is an overproduction of healthy skin cells and more T cells and white blood cells, which disrupts the skin-shedding cycle.

New skin cells reach the outermost layer of the skin too quickly: in days when this typically takes weeks.

Because the dead skin and white blood cells can't shed fast enough, they build up and create thick, scaly plaques on the surface of the skin.

Associated Conditions

There are several different types of skin rashes and conditions in which plaques may be present. These include:

Eczema

Eczema is also called atopic or allergic dermatitis. Rashes and plaques from eczema are related to an allergy to something which comes into contact with the skin.

Psoriasis

Psoriasis is a condition which affects roughly 2% of the population. Psoriasis rashes are related to a number of factors including immune system activity, genetic predisposition, and environmental components.

There are several different types of psoriasis, but plaque psoriasis (a.k.a. psoriasis vulgaris) is the most common form.

Pityriasis Rosea

Pityriasis rosea is a fairly short-term rash that occurs most often in older children and young adults.

The cause is not currently known, but it may be distinguished from some other skin conditions that cause skin plaques by the presence of a ​herald patch, a large and itchy patch that can be 1 to 5 inches in diameter, that occurs first.

Seborrheic Dermatitis

Seborrheic dermatitis is an inflammatory skin disorder affecting skin that has sebaceous glands. It is best known for being the condition that causes dandruff.

Tinea Versicolor

Tinea versicolor, also called pityriasis versicolor, is commonly confused with other rashes. It is a fungal infection caused by the yeasts Pityrosporum orbiculare and Pityrosporum ovale, which are found on the surface of the skin and in hair follicles. It becomes a problem only when there is an overgrowth of the fungus.

Since the culprit yeast turns off the production of melanin (the pigment that causes skin to tan), the rash is often hypopigmented, meaning it is lighter than surrounding skin.

There are many conditions that increase the risk of this condition, most notably pregnancy.

Ringworm

Ringworm, also known as tinea corporis, is another fungal infection that may be caused by several different fungi known as dermatophytes.

The fungi live on the dead cells on the surface of the skin and most commonly grow between the fingers and toes, and on the scalp.

The fungus thrives in a moist environment and often occurs in wrestlers due to close contact and sweating. Poor hygiene can also increase one's risk.

Diagnosis

Plaques are just one of the several types of primary lesions that indicate a skin disease. Plaques can be a bit of a challenge to diagnose because there are several skin conditions that can cause them. That said, there are some unique findings that can help tell these rashes apart.

For example, seborrheic dermatitis plaques are scaly, itchy, red and typically found on oily parts of the body, including the face and chest. Pityriasis rosea plaques begin with one herald patch and spread. The plaques also resemble drooping tree branches.

Tinea versicolor can be diagnosed using a Wood's lamp. (The rash glows a characteristic yellow under the lamp's black light.)

A KOH test may be positive with some of these conditions.

Treatment for Plaques on Skin

Skin plaques often respond to treatment with a topical cream or ointment, like a corticosteroid or retinoid. The full treatment plan, however, depends on the underlying skin disease.

Oral medication, like an antihistamine, may be prescribed to help control itching. Plaque psoriasis can be treated using light therapy.

Proper hygiene, regular use of a moisturizer, oatmeal baths, and sun exposure (while wearing sunscreen) are all said to ease discomfort and keep skin healthy, although they can't completely prevent plaques from occurring.