Parapsoriasis is the collective name for a group of skin conditions that resemble psoriasis, but may behave or present differently.
Parapsoriasis refers to a variety of inflammatory skin conditions that may have different causes. Because of this, there is no single definition for the term.
Parapsoriasis is rare, and occurs mainly in middle-aged people. It usually presents as lesions that are pink or dark in color and form scaly patches that vary in size. The disorder can be chronic, and typically resists treatment.
There are two types of parapsoriasis. Small plaque parapsoriasis (SPP) is a chronic, benign condition, meaning it is unlikely to become cancerous. Large plaque parapsoriasis (LPP) is often a premalignant dermatosis, meaning it has a higher risk of developing into cancer.
LPP is most likely to develop into a type of cancer called mycosis fungoides, which is a type of cutaneous T-cell lymphoma (CTCL). This is a slow growing cancer, involving some of the white blood cells as it becomes malignant. The abnormal cells move to the skin, and some remain there. About 10% of people with LPP progress to a malignant form of the disorder.
The name parapsoriasis comes from the similarity to psoriasis, as both disorders cause scaly plaques on the skin.
A key difference between the two disorders is that plaque coming from parapsoriasis is usually thinner than plaque from most typical forms of psoriasis. Treatment is often the same or similar for both disorders.
Small plaque parapsoriasis usually presents as yellow-brown or pink, rash-like patches that are oval or round with scaling. The lesions mainly appear on the abdomen, legs, or extremities. SPP is otherwise asymptomatic.
Plaques may also develop on areas of skin where specific nerves spread out from the spinal cord, and appear on the abdomen and back. This is also known as digitate dermatosis, as the plaques resemble fingers or digits.
Large plaque parapsoriasis usually causes larger, irregularly shaped patches that are brown or red with fine scaling. The skin in affected areas may also become thinner. People usually develop lesions in areas that have little exposure to sun, such as the thighs, buttocks, breasts, and lower abdomen.
LPP may be otherwise asymptomatic, but may develop into skin cancer. The plaques in both types of parapsoriasis may have a wrinkled, thinning appearance.
For a doctor or dermatologist to diagnose parapsoriasis, a person’s skin must show symptoms of either SPP or LPP.
A doctor or dermatologist will usually perform a punch biopsy, a type of biopsy, on an affected area of skin. This will allow them to see the full thickness of the skin and examine it under a microscope.
They may perform multiple biopsies in different areas of the skin, as parapsoriasis is a diverse condition. They may additionally recommend performing more biopsies over time to track and monitor how the condition progresses.
With phototherapy, a healthcare professional exposes the person’s skin to UVB light or UVA light. UVB light is a type of ultraviolet light on the spectrum between UVA rays, which cause tanning, and the more intense UVC rays.
Treatment for LPP is similar to SPP, starting with topical corticosteroids. However, a healthcare provider will usually prescribe a very high potency steroid for LPP, which the person should use for about 12 weeks.
If LPP is severe, a doctor will usually recommend phototherapy treatment 2–3 times a week.
People should see a healthcare provider for follow ups annually for SPP and every 6 months for LPP, due to the latter condition’s potential to progress into cancer.
Parapsoriasis is a chronic condition, meaning it can be recurring and lifelong. A person may need to seek a long-term management plan.
While SPP is a benign condition, LPP may become malignant, and develop into the cancer mycosis fungoides, or cutaneous T-cell lymphoma (CTCL).
It can be difficult for a doctor to diagnose CTCL because:
- blood tests may not reveal cancerous cells
- it often looks like a common skin condition such as psoriasis or eczema
- a skin biopsy often does not reveal cancer cells
Mycosis fungoides, the most common type of CTCL, develops slowly. This means that doctors or dermatologists diagnose about 70% of people while they are in the early stages of the cancer. Someone who begins treatment in the early stages of the cancer has a normal life expectancy.
If the cancer is more advanced, doctors will focus treatment on delaying the spread of cancer, reducing tumors, and improving the person’s quality of life. The cancer may have no cure, but doctors can effectively manage it.
Parapsoriasis is the name for a collection of skin conditions that are similar to psoriasis. While the two appear similar and have similar treatments, parapsoriasis causes thinner scaly plaques than psoriasis.
There are two types of parapsoriasis, which are known as large plaque and small plaque parapsoriasis. Large plaque parapsoriasis may become malignant, and develop into a cancer called cutaneous T-cell lymphoma. Small plaque parapsoriasis is a benign condition that is unlikely to cause any other issues.
Both types result in a pink or yellow-brown rash with scaly plaques on the skin.
A doctor or dermatologist will diagnose parapsoriasis by examining the skin, checking for symptoms, and most likely by performing a series of biopsies. They will treat the condition with corticosteroids, followed by phototherapy if necessary. They also will carefully monitor the person for signs of skin cancer.
Parapsoriasis is a chronic, lifelong condition that is possible to treat, but not cure. The large plaque variety may develop into an incurable but treatable cancer.