Pityriasis Rubra Pilaris: Introduction
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Epidemiology
Pityriasis rubra pilaris is a rare, chronic disorder with an estimated incidence ranging from 1 in 5,000 to 1 in 50,000 dermatology patients. The age distribution is bimodal with peak incidences in the first and fifth decades of life. The disease occurs in all races and affects the sexes equally.1
Etiology and Pathogenesis
Although an underlying dysfunction in vitamin A metabolism has been suggested, the etiology and pathogenesis of pityriasis rubra pilaris are still poorly understood. Thus, the role of vitamin A deficiency remains uncertain as attempts to produce keratotic lesions by vitamin A deprivation have been unsuccessful. Moreover, the deficiency of retinol-binding protein as an underlying pathogenic mechanism resulting in inadequate transport of vitamin A to the skin has yet to be ascertained. There are some cases in which pityriasis rubra pilaris may result from immune system dysregulation and abnormal response to various antigenic triggers.2 A report of an exanthematous form of juvenile pityriasis rubra pilaris that followed an upper respiratory infection and initially resembled Kawasaki disease supports the hypothesis of a superantigen-mediated process. Finally, genetic factors with an autosomal dominant pattern of inheritance have been supposed to play a critical role for the induction of pityriasis rubra pilaris. Nevertheless, affected relatives are not observed in the classical acute-onset disease and are infrequent in other variants.
Clinical Findings
Pityriasis rubra pilaris is generally believed to comprise more than a single entity and a classification scheme based on clinical characteristics and course has been proposed by Griffiths1 (Table 24-1).
Type | Description | % | Clinical Characteristics | Distribution | Course |
|---|---|---|---|---|---|
I | Classic adult | >50 | Erythroderma with islands of normal skin (“nappes claires”), follicular hyperkeratosis, waxy diffuse palmoplantar keratoderma | Generalized, beginning on the head and neck, then spreading caudally | Often resolves within an average period of 3 years |
II | Atypical adult | 5 | Combination of follicular hyperkeratosis and ichthyosiform lesions on the legs, sparse scalp hair | Generalized | Long duration (>20 years) |
III | Classic juvenile | 10 | Similar to type I but appears in years 1 or 2 of life | Generalized | Often resolves within an average period of 1–2 years |
IV | Circumscribed juvenile | 25 | Prepubertal children; well-demarcated scaly, erythematous plaques on the elbows and knees, resembling localized psoriasis | Localized | Uncertain, some cases clear in the late teens |
V | Atypical juvenile | 5 | Begins in first few years, accounts for most familial cases; follicular hyperkeratosis, scleroderma-like appearance of the hands and feet | Generalized | Chronic course, improvement with retinoids but relapses when stopped |
VI | HIV-associated | NAa | Similar to type I with variable beginning; associated with acne conglobata, hidradenitis suppurativa and lichen spinulosus | Generalized | May respond to antiretroviral triple therapy |
Type I (classic adult) is the most common subtype with over 50% of all cases. Characteristically, patients present with an eruption of follicular hyperkeratotic papules that spread in cephalocaudal direction (Fig. 24-1). As the disease further evolves, a reddish orange, scaling dermatitis appears that often progresses to a generalized erythroderma over a period of 2–3 months (Fig. 24-2). A diagnostic hallmark of pityriasis rubra pilaris are sharply demarcated islands of unaffected skin (“nappes claires”) in a random distribution (Fig. 24-2B). Many patients develop a waxy, diffuse, yellowish keratoderma of the palms and soles (Fig. 24-3).3 Nail changes are not uncommon and include distal yellow–brown discoloration, nail plate thickening, splinter hemorrhages, and subungual hyperkeratosis. Eventually, the mucous membranes may be affected with a diffuse whitish appearance of the buccal mucosa as well as lacy white plaques and erosions. Hair and teeth are normal.
Figure 24-2
