Pityriasis rosea is a benign, self-limited eruption that may occur at any age, with peak incidence during adolescence. A solitary, 2to 5-cm, pink, oval patch with central clearing, theso-called herald patch, is the first manifestation of the eruption.The herald patch typically is found on the breast, lower torso, orproximal thigh and is often misdiagnosed as fungal or eczematous in origin. One to 2 weeks later, a generalized eruptionoccurs on the torso and proximal extremities. Multiple 0.5to2-cm, oval to oblong, red or tan macules with a fine, branlikescale are characteristically arranged parallel to skin tensionlines (Christmas tree pattern). Rarely, the eruption may have aninverse distribution involving the axillae and groin or a papularor papulovesicular appearance. Mild prodromal symptoms maybe present with the appearance of the herald patch, and pruritusis present in 25% of cases. The eruption lasts 4 to 14 weeks, withgradual resolution. Residual hyperpigmentation or hypopigmentation can take additional months to clear. Treatment is unnecessary, though pruritus can be managed with oral antihistamines, phototherapy, and low-potency topical corticosteroids.
Psoriasis is a common papulosquamous condition characterized by well-demarcated, erythematous, scaling papules andplaques. Psoriasis occurs at all ages, including infancy, withonset of 30% of cases during childhood. The disease is characterized by a chronic and relapsing course, although spontaneous remissions can occur. Infections (especially Streptococcus pyogenes), stress, trauma, and medications may cause diseaseexacerbations. Various subtypes of psoriasis exist. The mostcommon variety is plaque-type psoriasis (psoriasis vulgaris), which can be localized or generalized. The lesions consist ofround, well-demarcated, red plaques measuring 1 to 7 cm withmicaceous scale, which is distinctive in its thick, silvery appearance with pinpoint bleeding points revealed on removal of thescales (Auspitz sign). The lesions of psoriasis have a distinctivedistribution involving the extensor aspect of the elbows andknees, posterior occipital scalp, periumbilical region, lumbosacral region, and intergluteal cleft. Children often have faciallesions involving the superomedial aspect of the eyelids. Nailplate involvement is common and includes pitting, onycholysis, subungual hyperkeratosis, and oil staining (reddish brownsubungual macular discoloration). Guttate (numerous smallplaques diffusely distributed on the torso), erythrodermic (covering large body surface areas), inverse (moist red patches affecting body folds), and pustular forms may occur.
The foundation of therapy is topical corticosteroids. Treatment of psoriasis with oral corticosteroids can induce pustularpsoriasis and should be avoided. Because of the risk of atrophy,striae, and telangiectases, especially when potent fluorinated corticosteroid preparations are administered long-term, thegoal is to use the least potent corticosteroid necessary. Topical vitamin D analogs, salicylic acid, and tar preparations areuseful adjuvants to topical corticosteroids. Phototherapy withultraviolet B (UVB) light can be useful as secondary therapy inolder children. Extensive plaque or guttate, erythrodermic, andpustular psoriasis may necessitate systemic treatments withimmune suppressive medication (methotrexate, cyclosporine,tumor necrosis factor-α antagonists). Disease triggers such asinfection or medications should be identified and removed.