Diseases of the Epidermis

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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).

Psoriasis is rare in neonates but may be severe and recalcitrant and may pose a diagnostic problem. Other rare forms include psoriatic erythroderma, localized or generalized pustular psoriasis, and linear psoriasis.

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 therapeutic approach varies with the age of the child, type of psoriasis, sites of involvement, and extent of the disease. Physical and chemical trauma to the skin should be avoided as much as possible (see previous discussion of Koebner response).

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.

The 2nd tier of therapy is phototherapy. Narrow-band ultraviolet B (UVB 311 nm; NB-UVB) irradiation is the primary form of UVB therapy used in childhood. It is as or nearly as effective as psoralen with UVA (PUVA), without the side effects associated with psoralen. If available, phototherapy should be used for children with extensive disease in whom topical therapy has failed. Excimer (308-nm) laser UVB irradiation may be used for localized treatment-resistant plaques. These treatments are time consuming and available only at limited locations.

The 3rd tier is systemic therapy. A few children with severe psoriasis require systemic therapy. Methotrexate (0.2 to 0.4 mL/kg once a week), oral retinoids (0.3 to 1.0 mg/kg/day), and cyclosporine (3-5 mg/kg/day) are used for the rare severe and generalized forms of psoriasis. Oral retinoids may be combined with phototherapy.

The 4th tier of therapy is the biologic response modifiers, including the tumor necrosis factor inhibitors etanercept, infliximab, and adalimumab and the T-cell function inhibitors efalizumab and alefacept. Ustekinumab, a human monoclonal antibody that prevents interactions between interleukins IL-12 and IL-23 and their cell surface receptor, has efficacy in treating moderate to severe chronic psoriasis and psoriatic arthritis.

649.2 Pityriasis Lichenoides

Pityriasis lichenoides encompasses pityriasis lichenoides acuta (PLA; pityriasis lichenoides et varioliformis acuta [PLEVA] and Mucha-Habermann disease) and PLC. The designation of pityriasis lichenoides as acute or chronic refers to the morphologic appearance of the lesions rather than to the duration of the disease. No correlation is found between the type of lesion at the onset of the eruption and the duration of the disease. Many patients have both acute and chronic lesions simultaneously, and transition of lesions from one form into another occurs occasionally. A rare variant, acute febrile ulcernecrotic Mucha-Habermann disease, is also included in the spectrum of pityriasis lichenoides.

Clinical Manifestations

Pityriasis lichenoides most commonly manifests in the second and third decades of life; 30% of cases manifest before age 20 yr.

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.

Acute febrile ulceronecrotic Mucha-Habermann disease manifests as fever and ulceronecrotic plaques up to 1 cm in diameter, which are most common on the anterior trunk and flexors of the proximal upper extremities. Arthritis and superinfection of cutaneous lesions with Staphylococcus aureus may also develop. The ulceronecrotic lesions heal with hypopigmented scarring in a few weeks.

649.3 Keratosis Pilaris

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