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PITYRIASIS RUBRA PILARIS
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Pityriasis rubra pilaris (PRP) is an inflammatory papulosquamous dermatosis of juvenile or adult onset. It is presenting with distinctive clinical features and a self-limiting or chronic evolution. The disease is subclassified into 6 types, including both hereditary and acquired forms. The hereditary form of PRP is linked to CARD14 gain-of-function mutations. The cause of the acquired forms I-IV is unknown. Type VI PRP is associated with HIV infection. Typical features are follicular hyperkeratotic papules that coalesce into scaly, reddish-orange–colored plaques. The disease may progress to erythroderma with well-demarcated islands of normal skin (“nappes claires”). Distinguishing PRP from psoriasis may pose a diagnostic challenge, particularly in early phases of the disease. Histopathologic examination reveals hyperkeratosis, alternating parakeratosis and orthokeratosis in a checkerboard pattern, with focal acantholytic dyskeratosis. The most successful treatment options are systemic retinoids, methotrexate as well as biologics; however, there is currently no FDA-approved therapy for PRP. Combining different systemic treatments or adjuvant photochemotherapy may be considered. See Table 7-1.
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