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| Fig. 7.5 Pityriasis rubra pilaris. A, Extensive involvement in adult showing characteristic salmon color and 'islands of sparing.' B, Characteristic thickened yellow palmar changes. |
Pityriasis rubra pilaris (PRP) is a rare disease in which the primary abnormality appears to be hyperproliferation of the epidermis (Fig. 7-5). Five variants have been described, the most common being type I, the classic adult-onset form. In this type, the eruption commonly begins on the head and neck as reddish-orange, slightly scaly macules and thin plaques. The rash extends in a cephalocaudal fashion, and within several weeks, red, perifollicular papules with central plugs develop in the lesions. The scalp often develops extensive yellowish scale. The palms and soles become thickened and yellow, which is called keratoderma. This results in a well-demarcated, very characteristic “PRP sandal.” Although total body involvement (erythroderma) is not uncommon, the rash of PRP often has characteristic skip areas of normal skin (“islands of sparing”). Considering that the rash usually looks very impressive, it is surprising that patients often complain of only mild irritation and pruritus.
