Pityriasis rubra pilaris (PRP) is a rare condition that is often initially mistaken for another skin disorder, usually psoriasis. The disease affects persons of all ages, races, and nationalities. Both sexes are affected equally. Many Support Group members report a varied clinical progression of the disease.
Several types of pityriasis rubra pilaris are now recognized:
- By far the most common is the classic adult type, which causes a widespread rash during adult life. A variation on this affects young children the classic juvenile type.
- Next most common is the circumscribed juvenile type that affects the palms and soles, and points of the knees and elbows of children.
- Finally there are two other types of pityriasis rubra pilaris that are less typical the atypical adult and atypical juvenile types. Both are too rare to be discussed further here.
The exact cause of this condition is simply not known. It is not an infection and hence cannot be passed on to others. Initially, the disorder is characterized by elevated spots (papules) on the skin. These spots grow and become connected, producing red plaques over large areas.
The eruption is limited in the beginning, having a predilection for the sides of the neck and trunk and the extensor surfaces of the extremities. Then, as new lesions occur, extensive areas are converted into sharply marginated patches of various sizes, which look like exaggerated goose-flesh and feel like a nutmeg grater.
Treatment is aimed at reducing the duration of disease and is often a challenge. A number of different therapeutic options have been reported in the literature with varying degrees of effectiveness.
In a study of patients with pediatric pityriasis rubra pilaris, isotretinoin achieved the best response among a range of therapies including steroids, systemic retinoids, and methotrexate; five of six patients treated with isotretinoin showed 90% to 100% clearing of lesions within 6 months of initiation of treatment.
Diagnosis is by clinical appearance and may be supported by biopsy. Differential diagnosis includes seborrheic dermatitis (in children) and psoriasis when disease occurs on the scalp, elbows, and knees. Treatment is exceedingly difficult and empiric. Disease may be ameliorated but almost never cured; classic forms of the disease resolve slowly over 3 yr, while nonclassic forms persist.
A more potent and more effective treatment is methotrexate tablets, but as these can have dangerous side effects they are saved for people who don't improve with the retinoids. Methotrexate may put the PRP into remission, so it goes away and stays away.