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  • Psoriasis affects 1.5–2% of the population in western countries. World wide occurrence.
  • A chronic disorder with polygenic predisposition and triggering environmental factors such as bacterial infection, trauma, or drugs.
  • Several clinical expressions. Typical lesions are chronic, recurring, scaly papules and plaques. Pustular eruptions and erythroderma occur.
  • Clinical presentation varies among individuals, from those with only a few localized plaques to those with generalized skin involvement.
  • Psoriatic arthritis occurs in 10–25% of the patients.
  • The pathogenesis is determined by a polygenic trait with an ongoing T cell–driven autoreactive immune response.

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Classification

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Psoriasis vulgaris

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   Acute guttate

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   Chronic stable plaque

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   Palmoplantar

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   Inverse

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Psoriatic erythroderma

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Pustular psoriasis

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   Pustular psoriasis of von Zumbusch

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   Palmoplantar pustulosis

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   Acrodermatitis continua

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ICD-9 : 696.1 • ICD-10 : L 40.0   Image not available. Image not available.

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Epidemiology

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Age of Onset

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Early: Peak incidence occurs at 22.5 years of age (in children, the mean age of onset is 8 years). Late: Presents about age 55. Early onset predicts a more severe and long-lasting disease, and there is usually a positive family history of psoriasis.

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Incidence

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Psoriasis affects 1.5–2% of the population in western countries. In the United States, there are 3 to 5 million persons with psoriasis. Most have localized psoriasis, but approximately 300,000 persons have generalized psoriasis.

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Sex

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Equal incidence in males and females.

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Race

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Low incidence in West Africans, Japanese, and Inuits; very low incidence or absence in North and South American Indians.

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Heredity

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Polygenic trait. When one parent has psoriasis, 8% of offspring develop psoriasis; when both parents have psoriasis, 41% of children develop psoriasis. HLA types most frequently associated with psoriasis are HLA- B13, -B17,-Bw57, and, most importantly, HLA-Cw6, which presents antigens to CD8+ T cells and is thus a candidate for functional involvement.

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Trigger Factors

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Physical trauma (Koebner phenomenon) is a major factor in eliciting lesions; rubbing and scratching stimulate the psoriatic proliferative process. Infections: acute streptococcal infection precipitates guttate psoriasis. Stress: a factor in flares of psoriasis is said to be as high as 40% in adults and higher in children. Drugs: systemic glucocorticoids, oral lithium, antimalarial drugs, interferon, and β-adrenergic blockers can cause flares in existing psoriasis and cause a psoriasiform drug eruption. Alcohol ingestion is a putative trigger factor.

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Pathogenesis

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The most obvious abnormalities in psoriasis are (1) an alteration of the cell kinetics of keratinocytes with a shortening of the cell cycle from 311 to 36 h, resulting in 28 times the normal production of epidermal cells, and (2) ...

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