What Is Parapsoriasis?

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Parapsoriasis is an umbrella term for a group of skin disorders characterized by a rash made up of scaly patches (plaques). There are two types of parapsoriasis: small-plaque parapsoriasis and large-plaque parapsoriasis.

Parapsoriasis is poorly defined, and its causes are largely unknown. Parapsoriasis isn't related to psoriasis even though they have similar names. While there is some overlap in symptoms, including the appearance of skin patches, parapsoriasis and psoriasis are two different conditions.

a woman scratching her arm

Suriyawut Suriya / EyeEm / Getty Images

Types

Small-plaque parapsoriasis (SPP) is usually benign but chronic. SPP is characterized by plaques less than 2 inches (5 centimeters) in diameter on the skin. The plaques of SPP can be all over the body, but they are most commonly located on the trunk.

Large-plaque parapsoriasis (LPP) is also chronic, but it's considered a premalignant dermatosis. LPP may progress to mycosis fungoides, the most common type of cutaneous T-cell lymphoma (CTCL), a form of cancer. People with LPP will have plaques that are larger than 2 inches in diameter on the skin. They are usually on the trunk, but they can also be present on the buttocks.

Pityriasis lichenoides, red patches that quickly evolve into papules 5 mm–15 mm (millimeters) in diameter, was included in earlier studies of parapsoriasis. However, due to disagreement among experts, it is no longer considered a type of parapsoriasis.

Symptoms

Like psoriasis, parapsoriasis shows up on the skin as a patchy rash referred to as plaques. Usually, the plaques are red or pink, but they can be brown or yellow. The number of plaques varies, and the plaques could be raised, bumpy, scaly, or wrinkly.

Other than visible symptoms, there are no other symptoms aside from occasional itching. SPP rarely progresses, while large-plaque parapsoriasis has the potential to progress. LPP presents similarly to the patch stage of mycosis fungoides, the most common form of a type of blood cancer called cutaneous T-cell lymphoma.

Under a microscope, parapsoriasis and psoriasis look different, but over time the plaques caused by psoriasis become much thicker than plaques caused by parapsoriasis. Additionally, psoriasis occurs most often in young adults and children, while parapsoriasis is most common among middle-aged men.

Causes

The cause of parapsoriasis is unknown. However, experts believe parapsoriasis is a stage in the continuum from chronic dermatitis to lymphoproliferative disorders, conditions in the blood involving uncontrolled growth of lymphocytes (white blood cells), including cutaneous T-cell lymphoma.

Diagnosis

To diagnose parapsoriasis, your healthcare provider will examine the plaques on your skin, considering where they appear on your body, their size, and their texture.

Sometimes a skin biopsy is required to confirm the diagnosis or rule out other conditions. A biopsy can check for cutaneous T-cell lymphoma as well.

Treatment

Treatment for small-plaque parapsoriasis may not be required, but your healthcare provider may recommend treatment with high-potency topical corticosteroids for up to 12 weeks. If this treatment doesn't clear up the plaques, your practitioner may recommend other treatments, including phototherapy, skin moisturizers, or a combination.

Large-plaque parapsoriasis usually requires treatment. Topical steroids also are used in LPP, at high potency and for up to 12 weeks.

People with parapsoriasis generally need follow-up care, especially those with LPP, to ensure their condition does not progress to malignancy.

Prognosis

The prognosis of SPP and LPP is unpredictable. This means follow-up visits with your healthcare provider are essential. There is a risk of SPP or LPP developing into cutaneous T-cell lymphoma, so skin biopsies may also be needed to track the progression of your condition.

Frequently Asked Questions

What is parapsoriasis?

Parapsoriasis is a group of skin disorders characterized by small to large plaques on the skin. These plaques are usually asymptomatic.

How likely is parapsoriasis to become lymphoma?

Progression to malignancy is seen most often in large-plaque parapsoriasis. One study found that 10% of people with small-plaque parapsoriasis and 35% of people with large-plaque parapsoriasis developed histologically confirmed mycosis fungoides, a form of cutaneous T-cell lymphoma.

What causes parapsoriasis?

The underlying cause of small-plaque and large-plaque parapsoriasis is unknown. Research is ongoing to identify the causes of parapsoriasis.

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3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. UpToDate. Parapsoriasis (small plaque and large plaque parapsoriasis). Updated April 14, 2021.

  2. American Osteopathic College of Dermatology. Parapsoriasis.

  3. Väkevä L, Sarna S, Vaalasti A, Pukkala E, Kariniemi AL, Ranki A. A retrospective study of the probability of the evolution of parapsoriasis en plaques into mycosis fungoides. Acta Derm Venereol. 2005;85(4):318-23. doi:10.1080/00015550510030087