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Pityriasis Rubra Pilaris - Submitted on: Thursday March, 14, 2002
Contributed by:John Bissonette, MD , Artur Zembowicz, MD, PhD
Pityriasis rubra pilaris (PRP) is an idiopathic, papulosquamous disease first described in 1835 by Claudius Tarral as a general psoriasis. Devergie later described PRP in 1857 who at that time named it pityriasis pilaris. It was not until 1889 after Besnier’s description that the disorder was called by its current name

Definition:
PRP is a rare, chronic disease of unknown etiology with a unique combination of features including thick, smooth, yellow palms and soles, erythroderma, and well defined “skip spots” of normal skin surrounded by a background of erythema and red follicular papules on the dorsal aspects of the proximal phalanges, elbows, and knees. PRP is subclassified into a number of types, with the classical adult PRP (type 1) and juvenile PRP being the most common.

Clinical Features:
PRP occurs equally in men and women with a bimodal age distribution with peaks in the first and fifth to sixth decades. Most cases are acquired, but about 7% of cases have a positive family history usually with autosomal dominant inheritance. Familial cases only manifest the nonclassical form of the disease (see below).
Classically PRP is characterized by follicular hyperkeratotic papules that coalesce into large, scaly, erythematous plaques. Clinically these lesions can mimic psoriasis, a generalized hypersensitivity reaction, erythrokeratoderma variabilis, follicular eczema, follicular ichthyosis, lichen planopilaris, seborrheic dermititis, and subacute cutaneous lupus erythematosus. Helpful distinguishing features include “islands” of spared skin within generalized erythroderma, follicular keratotic plugs, and an orange hue to the involved skin.


Histology:
Figures
(Click on an image for a larger view)
Figure 1
Figure 2
PRP is characterized by focal irregular acanthosis, alternating orthokeratosis and parakeratosis in both the vertical and horizontal directions, hypergranulosis, thick suprapapillary plates, short and thick rete ridges, and a sparse to moderate lymphocytic perivascular infiltrate of the dermis. The pattern of parakeratosis is the most specific histological clue (Figure 1). The hair follicles are dilated and filled by orthokeratotic follicular plugs that extend above the level of the adjacent epidermis (Figure 2). Sometimes there is a parakeratotic shoulder (parakeratotic mounds) at the edges of the follicular ostia. Nail changes include thickening of the nail plate and subungual hyperkeratosis.
Psoriasis is the main histological differential diagnosis. Features that help differentiate psoriasis from PRP are the Munro microabscesses, diminished granular layer, elongated thin rete ridges, and vascular ectasia of the dermal papillae in close apposition to the thin rete ridges. All these features are found in psoriasis and not PRP. Recently acantholysis and focal acantholytic dyskeratosis have been described in PRP. These features are not seen in psoriasis, and thus are very helpful in distinguishing between the two entities.


Treatment:
Historically, large (and sometimes toxic) doses of Vitamin A were standard. Today oral synthetic retinoids are the treatment of choice, but successful treatment has been described using a number of immunosuppressive drugs (methotrexate, azathioprine, and cyclosporine) as well as PUVA therapy.

Bibliography:
  • Albert MR, Mackool BT. Pityriasis rubra pilaris. Int J Dermatol, 1999; 38(1): 1-11.
  • Soeprono FF. Histologic criteria for the diagnosis of pityriasis rubra pilaris. Am J Dermatopathol, 1986; 8: 277-283.
  • Sonex TS. Nail changes in adult type I pityriasis rubra pilaris. J Am Acad Dermatol, 1986; 15: 956.
     

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