White : Diseases of the Skin - Psoriasis and Related Disorders

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Gary M. White & Neil H. Cox

Diseases of the Skin

7	Psoriasis and Related Disorders

PITYRIASIS RUBRA PILARIS

Etiology and pathogenesis

Pityriasis rubra pilaris (PRP) is an uncommon but often characteristic dermatosis of unknown etiology. Most patients present in mid-childhood or in late middle age.

Clinical features

Pityriasis rubra pilaris resembles psoriasis in many respects, and many of the treatments are similar. Useful features that help to distinguish PRP (Fig.7.31) from psoriasis are the follicular prominence (especially in the localized types and the initial lesions of the generalized types), the orange color of the palmar involvement, the islands of sparing that occur in the generalized types, and the absence of typical psoriatic pits in the thickened nails.

Figure. 7.31 Pityriasis rubra pilaris (PRP). ( f ) Localized PRP in a child. ( g ) Confluent and follicular PRP of acute onset in a child. ( h ) The Koebner reactionalso occurs in this condition, as shown here in a teenaged patient.

Pityriasis rubra pilaris has classically been divided into five types (Griffiths), with more recent addition of HIV-associated PRP.

I. Classic adult type

II. Atypical adult type

III.Classic juvenile type

IV.Circumscribed juvenile type

V.Atypical juvenile type

VI. HIV-associated type

Differential diagnosis

The differential diagnosis is that of psoriasis (see earlier discussion of clinical features), of erythroderma (Table 7.4), or of acquired palmoplantar keratodermas (see later in this chapter), depending on the mode of presentation. Note that many of the palmoplantar keratodermas are inherited and develop in early years of life with a positive family history, thus distinguishing them from PRP.

The islands of sparing that occur in generalized PRP are not a feature of other erythrodermas, although this may be difficult to determine in the evolving suberythrodermic patient. A useful diagnostic feature is that PRP tends to spread from the head downward, often over a few weeks; although the head may be involved initially in generalized seborrheic dermatitis, this often involves flexures also, evolves less rapidly, and spares the palms and soles.

Treatment

Treatment is generally similar to that for psoriasis (see following section), but PRP is often both widespread and relatively refractory to therapy, so there is a much greater likelihood that systemic therapies will be required. In adults, acitretin is often used; other options include UVB, PUVA, methotrexate, or ciclosporin. Photoaggravation may limit use of UVB. In young women, the need to avoid pregnancy for 2 years after taking acitretin is a major limitation, and isotretinoin has been used as an alternative in this group. The juvenile-onset types often resolve in the teenage years, and systemic therapy may not be required, but the prognosis in individuals who develop PRP in the second half of childhood is less predictable.