Pityriasis Rosea, Pityriasis Rubra Pilaris, and Other Papulosquamous and Hyperkeratotic Diseases
Pityriasis rosea presents with erythematous macules that develop a delicate central silver scale. As the lesions evolve, they assume an oval configuration often best observed on the back and flanks. The scale becomes a peripheral collarette as the lesions evolve. Histologically, erythrocyte extravasation is characteristic, and clinically purpuric lesions may occasionally be noted. In patients with darker skin, the lesions of pityriasis rosea may assume a papular appearance. A more characteristic oval character is often evident on the upper flank near the axillary vault and can be helpful in confirming the diagnosis.
Pityriasis rubra pilaris (PRP) may present with classic nutmeg-grater, spiky, keratotic papules involving the dorsal digits, or may present with more subtle erythema and scale involving the hands, face, and scalp. Evolution can be rapid, and the patient can assume the appearance of erythroderma with characteristic islands of sparing. The eruptions often have a distinctly orange appearance, especially on the palms. Juvenile forms of PRP can present with nummular arrays of spiky papules or with hyperkeratotic plaques involving the extensors in a pattern reminiscent of psoriasis. Discrete keratotic follicular papules are often present at the periphery and are helpful in establishing the correct diagnosis without the need for biopsy. This portion of the atlas will guide you through the various clinical presentations of these disorders.