Pityriasis rubra pilaris

Pityriasis rubra pilaris (PRP) is a rare chronic inflammatory skin disorder characterized by reddish-orange scaly patches, follicular keratotic papules (small rough bumps centered on hair follicles), and palmoplantar keratoderma (thickening of the skin on the palms and soles). The condition primarily affects the skin and can range from localized patches to widespread involvement covering most of the body surface (erythroderma). A hallmark feature of PRP is the presence of well-demarcated "islands of sparing" — areas of normal-appearing skin surrounded by affected skin. The nails may also be affected, showing thickening, discoloration, and ridging. PRP is classified into six types (I through VI) based on age of onset, clinical features, and prognosis. Type I (classic adult) is the most common form, typically presenting in adulthood and often resolving spontaneously within a few years. Type III (classic juvenile) presents in childhood and also tends to resolve. Types II and V are chronic forms in adults and children respectively, while Type IV (circumscribed juvenile) is a localized form. Type VI is associated with HIV infection. The familial form, which accounts for a small proportion of cases, is typically inherited in an autosomal dominant pattern and has been linked to mutations in the CARD14 gene. Treatment of PRP can be challenging and varies depending on disease severity and type. Topical therapies including emollients, corticosteroids, and vitamin D analogues may be used for mild disease. Systemic treatments include oral retinoids (such as acitretin or isotretinoin), which are considered first-line therapy for moderate to severe disease. Methotrexate, cyclosporine, and biologic agents (particularly TNF-alpha inhibitors and IL-17 or IL-23 inhibitors) have also been used with varying success. Phototherapy may be beneficial in some patients, though it can occasionally worsen the condition. The prognosis varies by type, with some forms resolving spontaneously and others persisting chronically.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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