Skin patches, or plaques, that are common in psoriasis also occur with other skin diseases. Among them is parapsoriasis, which is not a single condition but, rather, an umbrella term for several skin diseases. In Greek, “para” means “next to” or “alongside.” In medicine, “para” indicates a condition that is like another.
The main difference between parapsoriasis and psoriasis is that parapsoriasis plaques tend to be thinner. The cause of parapsoriasis is unknown, but — just like psoriasis — parapsoriasis is not contagious.
In dermatology, parapsoriasis comprises several uncommon inflammatory skin diseases that differ from one another regarding symptoms, histopathology (effect on tissues), and treatment.
There are two main types of parapsoriasis: small plaque parapsoriasis (SPP) and large plaque parapsoriasis (LPP). Although pityriasis lichenoides was listed as a type of parapsoriasis in the past, dermatologists no longer consider this to be true.
SPP is characterized by asymptomatic, scaly, discolored patches that are less than 2 inches (5 centimeters) in diameter. These round or oval patches can be pink or yellowish brown. SPP tends to affect the chest, back, shoulders, and abdomen, but in rare cases, it appears on the arms and legs.
SPP is usually benign (noncancerous) and can last from two to three months. According to a study published in the journal Skinmed, it mainly affects men past their 50s. Examples of SPP include the following skin diseases:
Large Plaque Parapsoriasis
LPP, also called parapsoriasis en plaques, causes larger (more than 2 inches or 5 centimeters) scaly plaques than SPP does. With LPP, large oval or irregular-shaped, yellow-orange to red plaques show up on the trunk, legs, and arms. Like SPP, LPP has a higher incidence in men past middle age, according to the authors of the Skinmed article.
Examples of LPP include:
LPP may progress into mycosis fungoides, a form of cutaneous T-cell lymphoma (CTCL). This rare type of cancer begins with certain white blood cells called T cells or T lymphocytes. These cells typically help your body’s immune system, but in CTCL, they are abnormal and attack the skin. According to researchers, 10 percent of people with LPP develop mycosis fungoides. Some scientists believe that LPP is simply an early stage (also referred to as the patch stage) of mycosis fungoides.
Diagnosing parapsoriasis may involve a physical exam by a dermatologist, as well as a biopsy and genetic and molecular testing to rule out CTCL. The process of diagnosing a medical condition includes making a differential diagnosis — a list of other health conditions that may also explain the signs or symptoms a person is experiencing. Sometimes, conditions on this list need to be ruled out before a doctor can diagnose what they think is the most likely condition. In addition to ruling out CTCL, your doctor will want to check off various skin conditions, including other types of psoriasis.
Treatment for parapsoriasis varies based on the specific diagnosis. SPP may not require medical treatment because it is a benign (noncancerous) condition that may go away on its own. Generally, managing SPP focuses on relieving symptoms. Your doctor may recommend that you use topical corticosteroids, moisturizers, or phototherapy.
Follow-up appointments are recommended yearly for people living with SPP, but your doctor may follow a different schedule. Certain changes to the skin may prompt your doctor to biopsy the skin to check for a cancerous skin condition.
LPP often requires more aggressive therapy to prevent it from progressing to a cancerous skin condition. Treatments for LPP include:
Ask your doctor how frequently you should have follow-up appointments. Individuals using topical treatments may need to be seen more often than those treated with phototherapy. In general, you can expect follow-ups at least twice a year to assess your skin. Changes in your symptoms may prompt your doctor to order additional biopsies to check for mycosis fungoides.
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