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Psoriasis is a hereditary disorder of skin characterized by chronic scaling papules and plaques in a characteristic distribution, largely at sites of repeated minor trauma. The HLA types most frequently associated with psoriasis are HLA-B13, -B17, -Bw16, -B37, -Cw6, and DR7.


It can be difficult to distinguish between atopic dermatitis and psoriasis in infancy. If family history and cutaneous findings are not helpful, one hint is atopic dermatitis usually spares the diaper area and psoriasis favors that location.


Age 10% have onset of lesions before age 10, and 37% have onset before age 20.

Gender F > M, 2:1.

Prevalence 2% of the world’s population. United States and Canada: 4% to 5% of the population.

Race Low incidence in Asians, Africans, African Americans, American Indians, and Japanese.

Other Features Multifactorial inheritance. Minor trauma is a major factor (45% of patients) in eliciting lesions (Koebner’s phenomenon). Infection (particularly streptococcal) also plays a role. Many episodes of psoriasis follow sore throats or upper respiratory infections. Stress, cold weather, hypocalcemia, and lack of sunlight exposure aggravate the condition. Certain drugs (lithium, interferon, β-blockers, alcohol, antimalarials, corticosteroid withdrawal) can also precipitate psoriasis.


Psoriasis is likely a polygenic disease caused by the inappropriate activation of T cells (the adaptive immune system) as well as abnormal keratinocyte proliferation (the innate immune system).


Onset of Lesions Usually, months but may be sudden as in acute guttate psoriasis and generalized pustular psoriasis (von Zumbusch).

Skin Symptoms Pruritus is reasonably common, especially in scalp and anogenital psoriasis.

Constitutional Symptoms In 5% of cases, psoriasis can be associated with arthritis, fever, and/or an “acute illness” syndrome (weakness, chills, fever) with generalized erythroderma.

Physical Examination

Skin Findings

Type Well-delineated, erythematous, thickened plaques with a characteristic silvery-white scale (Fig. 4-1A). Removal of scale results in the appearance of miniscule blood droplets (Auspitz sign).


Psoriasis vulgaris A. Well-delineated erythematous plaques with a silvery-white scale characteristic of psoriasis. B. Well-delineated erythematous plaque located on the elbow of a child with psoriasis. Psoriasis vulgaris, scalp, and nail findings. C. Diffuse erythema and scale in the scalp of a child with psoriasis. Hair loss is minimal. D. Pinpoint pits, distal onycholysis, and yellowish discoloration (so-called oil-spot) seen in the fingernails of a child with psoriasis.

Color Salmon pink to red.


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