Definition:

Pityriasis rubra pilaris (PRP) is a spectrum of rare chronic inflammatory disorders with papulosquamous eruptions of unknown cause. The prototypical clinical characteristics of PRP are follicular hyperkeratotic papules on an erythematous base that can eventually coalesce to large red plaques. Its classification into five subgroups is based on age at onset, clinical course, morphologic features, and prognosis. More than 50% of patients are best classified as type I with adult-onset PRP. It is comprised of widespread, follicular papules and plaques and tends to clear spontaneously in 80% of patients in one to three years. Type II, which is the atypical adult subtype, tends to be more chronic and presents with areas of alopecia, eczematous patches, and a palmoplantar keratoderma. The classic juvenile type III is observed in only 10% of patients. It is similar clinically to type I but occurs in children and tends to remit in one year. Type IV, which is the circumscribed, juvenile subtype, presents with sharply-demarcated areas of follicular hyperkeratosis and erythema of the elbows and knees. An estimated 5% of children with PRP develop an atypical form classified as juvenile type V. Most familial cases that are published belong to this group. Recently, the designation of a new category of PRP (type VI) has been proposed that is characterized by the presence of HIV infection with different clinical features and a poorer prognosis. Treatment of PRP can be difficult, and no standardized approach has been established, although systemic retinoids are considered first-line therapy. Cyclosporin, methotrexate, and azathioprine are alternatives.