Pityriasis lichenoides is the name given to an uncommon rash of unknown cause. Its chronic (longer-lasting) form is known as pityriasis lichenoides chronica ( PLC ). The more acute (sudden onset) form is known as pityriasis lichenoides et varioliformis acuta ( PLEVA ), also known as Mucha-Haberman disease . Sometimes these conditions overlap and features of both may be seen in the same person.
Pityriasis lichenoides is probably a hypersensitivity reaction to a mild infection, but no specific bacteria or virus has yet been identified. It is not considered to be contagious. Pityriasis lichenoides most often affects adolescents and young adults. It is slightly more common in males. It is rare in infants and in old age. The person usually feels quite well, but occasionally the outbreak of skin lesions is accompanied by a mild headache or fever, especially with PLEVA.
PLC tends to have small, round, dusky pink, scaly lesions. The scaling spots flatten out over several weeks, leaving brown discoloration, which fades slowly over several months. Like PLEVA, PLC may last for several months.
PLEVA lesions are itchy, crusted (scabbed) red bumps or blisters, which heal to leave small scars. It looks very similar to chicken pox. PLEVA may also cause mouth ulcers. Most often, the lesions occur on the trunk, thighs and upper arms, but may appear anywhere on the body. It may last for months or even several years, with crops of new lesions appearing every few weeks. The diagnosis may need to be confirmed by a skin biopsy.
Pityriasis lichenoides may not always respond to treatment and it may return when treatment is stopped. If the rash is not bothering you, treatment may not be necessary.