Case of the Month

44 year old man presents with a red, mild-moderately pruritic rash on his chest with ‘islands of skin’ that are spared from the rash. It started about 2-3 months ago. He also complains that the skin on his palms looks slightly orange, and feels thicker.

What's Your Diagnosis?

Diagnosis: Pityriasis Rubra Pilaris

(Upon initial clinical examination I considered SCLE, psoriasis, and also psoriasiform dermatitis (although some consider pityriasis rubra pilaris to be a type of psoriasiform dermatitis)) .

The biopsy was consistent with Pityriasis Rubra Pilaris

Definition

An inflammatory process in which lesions present themselves clinically as red macules and subtle scaly papules. They soon become so confluent that there is widespread redness and scaling punctuated by islands of skin that ostensibly are

Course

The first lesion of pityriasis rubra pilaris to present themselves are red macules that may become scaly patches, or papules that may become scaly plaques. The disease tends to become progressively widespread and, in time, an erythroderma may result. Characteristically, there are zones within the erythroderma of seeming unaffected skin (“islands of spring”). The scaling becomes ever more marked and is expressed most dramatically on the scalp. Palms and soles become hyperkeratotic and have a yellow-orange cast. In addition, ostia of follicles often are seen to be widened and plugged by horny material.

Pityriasis rubra pilaris usually lasts for months, but sometimes for years.

Integration: Unifying Concept

Pityriasis rubra pilaris is a distinctive inflammatory process whose morphologic features are unique, clinically and histopathologically. Papules of the condition are characterized by discrete foci of parakeratosis that alternate with orthokeratosis in both vertical and horizontal directions. The granular zone is prominent and the remainder of the epidermis is psoriasiform, rete ridges of the condition being less long and more broad than those of psoriasis. A sparse infiltrate of lymphocytes is present around dilated venules of the superficial plexus. Tissue sections of the biopsy specimen of a horny plug within the ostium of a follicle show a dilated infundibulum filled with corneocytes that are both orthokeratotic and parakeratotic and arranged in a manner similar to that in the altered stratum corneum.

Pityriasis rubra pilaris, especially in its erythroderma expression, could be confused clinically, at first glance, with psoriasis, but the latter disease does not show “islands of sparing,” follicular accentuation, or palmer displays histopathologically, in addition to thin rete ridges, this suprapapillary plates, a mostly absent granular zone, and near confluent parakeratosis that houses some neutrophils. In sum, despite similarities clinically and histopathologically, pityriasis rubra pilaris and psoriasis are very different diseases.

The cause of pityriasis rubra pilaris is not known.

Therapy

Topical corticosteroids are appropriate for localized scaly papules and plaques on the extremities, but PUVA or retinoids given systemically are necessary for treating widespread lesions. Extracorporeal photophoresis and cyclosporine also have been advocated for disease that is widespread.

Reference

A CLINICAL ATLAS OF 101 COMMON SKIN DISEASES
With Histopathologic Correlation
A. BERNARD ACKERMAN, HELMET KERL, JORGE SANCHEZ, YING GUO, ANGELIKA HOFER, PAUL KELLY, TETSU KIMURA, GIOVANNI BORRONI,CHARLES CRUTCHFIELD, VOLKER STEINKRAUS, WOLFGANG WEYERS

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