Chapter 649 Diseases of the Epidermis
649.1 Psoriasis
Clinical Manifestations
This common, chronic skin disorder is first evident in ≈ 30% of affected individuals within the first 2 decades of life. The lesions consist of erythematous papules that coalesce to form plaques with sharply demarcated, irregular borders. If they are unaltered by treatment, a thick silvery or yellow-white scale (resembling mica) develops (Fig. 649-1A). Removal of the scale may result in pinpoint bleeding (Auspitz sign). The Koebner, or isomorphic, response, in which new lesions appear at sites of trauma, is a valuable diagnostic feature. Lesions may occur anywhere, but preferred sites are the scalp, knees, elbows, umbilicus, superior intergluteal fold, and genitals. Small raindrop-like lesions on the face are common. Nail involvement, a valuable diagnostic sign, is characterized by pitting of the nail plate, detachment of the plate (onycholysis), yellowish brown subungual discoloration, and accumulation of subungual debris (Fig. 649-1B).
Guttate psoriasis, a variant that occurs predominantly in children, is characterized by an explosive eruption of profuse, small, oval or round lesions that morphologically are identical to the larger plaques of psoriasis (Fig. 649-1C). Sites of predilection are the trunk, face, and proximal portions of the limbs. The onset frequently follows a streptococcal infection; a culture of the throat and serologic titers should be obtained. Guttate psoriasis has also been observed after perianal streptococcal infection, viral infections, sunburn, and withdrawal of systemic corticosteroid therapy.
Treatment
The treatment of psoriasis should be viewed as a 4-tier process. The 1st tier is topical therapy. Topical corticosteroid preparations are effective. Mid-potency or stronger topical steroids are necessary (Chapter 638). The preparation that is least potent but effective should be applied twice a day. The topical vitamin D analog calcipotriene is also effective. Calcipotriene can burn and sting, limiting its usefulness in children. One commonly used strategy is to use calcipotriene twice a day on weekdays and a high- to super-potency topical steroid twice a day on weekends. Tazarotene, a topical retinoid, is also useful. It may be used alone or in combination with other topical modalities. Tar preparation and anthralin may also be used. For scalp lesions, applications of a phenol and saline solution (e.g., Baker Cummins P & S Liquid) followed by a tar shampoo are effective in the removal of scales. A high- to super-potency corticosteroid in a foam, solution, lotion, or gel base may be applied when the scaling is diminished. Nail lesions are difficult to treat but may respond to topical tazarotene.
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649.2 Pityriasis Lichenoides
Clinical Manifestations
PLC manifests as generalized, multiple, 3- to 5-mm brown-red papules that are covered by a fine grayish scale (Fig. 649-2). Lesions may be asymptomatic or may cause minimal pruritus and occasionally become vesicular, hemorrhagic, crusted, or superinfected. Individual papules become flat and brownish in 2-6 wk, ultimately leaving a hyperpigmented or hypopigmented macule. Scarring is unusual. Lesions are most common on the trunk and extremities and generally spare the face, palmoplantar surfaces, scalp, and mucous membranes.
PLA manifests as an abrupt eruption of numerous papules that have a vesiculopustular and then a purpuric center, are covered by a dark adherent crust, and are surrounded by an erythematous halo (Fig. 649-3). Constitutional symptoms such as fever, malaise, headache, and arthralgias may be present for 2-3 days after the initial outbreak. Lesions are distributed diffusely on the trunk and extremities, as in PLC. Individual lesions heal within a few weeks, sometimes leaving a varioliform scar, and successive crops of papules produce the characteristic polymorphous appearance of the eruption, with lesions in various stages of evolution. The overall eruption persists for months to years.
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