Pityriasis lichenoides

 The cause of pityriasis lichenoides is not known. It has been reported to occur in the setting of recent bacterial or viral infections and may represent a reaction to infections.

Pityriasis lichenoides most often affects adolescents and young adults and seems to be slightly more common in males of all skin groups.

Is it hereditary?

No.

The acute form (PLEVA): Initially, it has been associated with feeling generally unwell with a fever. The rash starts as flat pink or discoloured spots, which may quickly become more inflamed and/or blister and blood-stained crusting may develop. The spots may come up in crops at different times, so the rash often consists of spots at various stages of development. PLEVA can often be mistaken for chickenpox but it takes much longer to clear than chickenpox. The spots are usually scattered on the trunk, arms, and legs. In children, spots may appear more on the face than at other areas of the body. Scarring and changes in skin colour may occur when the crust falls off.

The chronic form (PLC): The spots look less red or inflamed than in PLEVA and are covered with a firm shiny scale (flake) of skin. The scale can be scraped off by a dermatologist to reveal a shiny, red-brown, or discoloured surface underneath, and may help with confirming the diagnosis. Individual spots flatten within 3 to 4 weeks and the scale becomes loose, often leaving temporary marks which appear darker than the individual’s skin colour. The marks gradually fade away. However, new spots may then appear. Scarring is less likely in PLC than PLEVA. The signs of PLC may be more subtle in more deeply pigmented skin.

What are the symptoms of pityriasis lichenoides?

No symptoms are often experienced in PLC, but in PLEVA, the spots may itch, irritate, or cause a burning sensation as they appear.

Images DermNetNZ.

The appearance of the rash will suggest the diagnosis. However, PLEVA can often look like chickenpox but take much longer to clear than chickenpox, and PLC can look like psoriasis (red, flaky, crusty patch of skin covered with silvery scales). The examination under the microscope of a small sample of the rash (a skin biopsy) taken by a dermatologist can confirm the diagnosis.

Can pityriasis lichenoides be cured?

No treatment is certain to cure the condition. New spots may stop developing after a few weeks, with many cases clear within 6 months. However, the rash may come back and some cases of PLEVA and PLC can wax and wane for several years. The reason for this is currently unknown.

How can pityriasis lichenoides be treated?

No treatment is required if the rash is mild and not causing any symptoms, such as itch, but if you are concerned, you may need to seek advice from your doctor.