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Parapsoriasis is a skin condition that closely resembles psoriasis to the eye, but looks different under a microscope and has different underlying causes.

Parapsoriasis causes scaly lesions called plaques to form on the body. It’s important to tell the difference in parapsoriasis from psoriasis because one form of parapsoriasis causes an increased incidence of cancer.

Discover more about parapsoriasis, including its types and your treatment options.

Parapsoriasis is the result of an interaction between skin cells and the immune system that causes the skin to build up excess cells, creating plaques. Doctors may also call this condition parapsoriasis en plaques or Brocq’s disease.

Parapsoriasis may look like psoriasis, but its underlying cause is a disorder in immune system cells called T cells that are located in the skin. Psoriasis is related to specific T cells, particularly the Th1 and Th17 cells in the body.

As a general rule, the plaques or scaly patches that form with parapsoriasis are usually thinner than with psoriasis.

Dermatologists classify parapsoriasis into two types:

  • small-plaque parapsoriasis (SPP)
  • large-plaque parapsoriasis (LPP)

A doctor will take a skin sample called a biopsy, then examine the skin under a microscope to determine what type it is. To ensure a correct diagnosis, a doctor will usually take multiple biopsies.

Here are some key differences between the two parapsoriasis types.

While the lesions from parapsoriasis are noticeable, they don’t usually cause pain. However, some people may report itching.

Small-plaque parapsoriasis (SPP)

What it looks like

SPP causes the following symptoms:

  • pink to yellow-brown lesions
  • round or oval in shape
  • raised patches or flat, discolored patches called macules
  • about 2 to 5 centimeters in size

Where SPP is found

Doctors usually identify SPP lesions on the trunks, flanks, and arms and legs, close to the trunk.

Implications

Although SPP is a chronic condition, it’s benign. It does not typically progress to cancer as LPP can. There is also a sub-type of SPP that doctors call digitate dermatosis. These lesions are usually longer, thin patches that often occur on the sides of the body.

Large-plaque parapsoriasis (LPP)

What it looks like

LPP typically appears like the following:

  • large, irregularly shaped patches
  • patches that are either brown-red or brown in color
  • usually greater than 6 centimeters in diameter

Where LPP is found

Doctors usually find LPP on areas where the sun doesn’t hit the skin. These may include the buttocks, under the breasts, thighs, and area under the buttocks.

Implications

LPP can progress to a cancerous condition in about 20 to 30 percent of cases. One of these forms is T-cell lymphoma, a rare skin cancer, that may appear as a skin condition called mycosis fungoides.

Doctors don’t know why some people get parapsoriasis. They haven‘t identified specific causes, which means you can’t prevent the condition from occurring.

Gender is one of the greatest risk factors for parapsoriasis. An estimated two-thirds of all people who get the skin condition are men, according to the American Osteopathic College of Dermatology. The condition also tends to affect those between 40 and 50 years old.

Because doctors don’t know exactly why some people get the condition, there aren’t risk factors you can change that would keep you from getting parapsoriasis.

Treatments for parapsoriasis depend upon what type a person has and what their symptoms are.

SPP

A person can elect not to use any special treatments for SPP. However, they can utilize emollients (such as petroleum jelly) applied to the skin if they wish to treat it over the counter. These lock in moisture in the skin.

Treatments for SPP usually start with application of strong, prescription-only topical corticosteroids. You will apply these daily for about 8 to 12 weeks.

A dermatologist will then evaluate your skin. If your parapsoriasis areas haven’t improved by 50 percent, a dermatologist will usually recommend light therapy. This involves exposing the skin to ultraviolet light via a special light box for about 2 to 3 times a week.

You’ll typically visit your dermatologist at least once a year (more often if you have a flare-up) to review your parapsoriasis symptoms.

LPP

Dermatologists will usually prescribe strong corticosteroids to apply topically for about 12 weeks. If you have a significant number of LPP lesions, your doctor may start with phototherapy 2 to 3 times a week.

While doctors may initially treat LPP similarly to SPP, a doctor will usually have you follow up at least every 6 months to ensure your skin condition doesn’t progress to cancer.

If you have LPP, your doctor will have you come for skin checks regularly to ensure the condition hasn’t progressed to a cancerous form. While not everyone who has LLP will develop cancer, there is no way to predict if the condition will progress, and there is no way to prevent this change from occurring.

Long-term use of topical steroids to treat parapsoriasis can cause unwanted side effects. Examples include thinning skin, stretch marks or striae, visible spider veins, and even a reduction in hormones from the adrenal glands, called adrenal suppression. For this reason, a doctor will generally prescribe steroids for use for the shortest duration possible.

Parapsoriasis is a rare skin condition. The SPP type doesn’t usually progress to cancer, but it can still cause itching or make a person feel self-conscious about their lesions.

Because the LPP type can progress to cancer, it’s important to be treated by a doctor regularly. If you have a skin condition you’re unsure about, see your dermatologist for an examination and an accurate diagnosis.