Pityriasis rubra pilaris (PRP) was first described in 1828 by Tarral and was named by Besnier in 1889. It is a chronic papulosquamous disorder of unknown etiology characterized by reddish orange scaly plaques, palmoplantar keratoderma, and keratotic follicular papules. The disease may progress to erythroderma with distinct areas of uninvolved skin, the so-called islands of sparing.
Griffiths divided pityriasis rubra pilaris into 5 categories: classic adult type, atypical adult type, classic juvenile type, circumscribed juvenile type, and atypical juvenile type. [1, 2] More recently, an HIV-associated type has been added to this classification system. [3, 4, 5, 6]
The etiology is unknown. A familial form of the disease exists, with an autosomal dominant inheritance pattern. Recently, the inherited form of PRP was linked to mutations in the gene, CARD. [9, 10] Most cases of PRP are sporadic, however.  One hypothesis is that pityriasis rubra pilaris may be related to an abnormal immune response to an antigenic trigger. Case reports have described pityriasis rubra pilaris occurring after streptococcal infections. 
The incidence of pityriasis rubra pilaris has been reported to be 1 case in 3500-5000 patients presenting to dermatologic clinics.
Persons of any race can be affected.
Pityriasis rubra pilaris occurs equally among men and women. 
The familial form of pityriasis rubra pilaris typically begins in early childhood and has an autosomal dominant inheritance pattern.
The acquired form of pityriasis rubra pilaris has a bimodal age distribution, with peaks in the first and fifth decades of life, but it can begin at any age.
Each type of pityriasis rubra pilaris has its own prognosis. In general, the familial form of the disease may be persistent throughout life, and the acquired form of the disease may resolve spontaneously within 1-3 years. Patients with pityriasis rubra pilaris can have painful and disabling palmoplantar keratoderma. Nail dystrophy and shedding may be present. However, most of the morbidity associated with pityriasis rubra pilaris is associated with the erythroderma (see Complications).
The prpAlliance (http://prpalliance.com/) is a nonprofit, patient advocacy organization. Their Web site is currently offline, but it directs the reader to the PRP Community on RareConnect (see https://www.rareconnect.org/en/community/pityriasis-rubra-pilaris). Additionally, there is a PRP Facebook Support Group, founded in 2013, for patients and caregivers.
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