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PSORIASIS

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  • Psoriasis affects 1.5 to 2% of the population in Western countries but has worldwide 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 erythroderma is psoriasis involving the entire skin.

  • Psoriatic arthritis occurs in 10 to 25% of patients.

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CLASSIFICATION

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  • Psoriasis vulgaris

    • Acute guttate

    • Chronic stable plaque

    • Palmoplantar

    • Inverse

  • Psoriatic erythroderma

  • Pustular psoriasis

    • Pustular psoriasis of von Zumbusch

    • Palmoplantar pustulosis

    • Acrodermatitis continua

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PSORIASIS VULGARIS ICD-10: L40.0

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EPIDEMIOLOGY

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AGE OF ONSET All ages. Early: Peak incidence occurs at 22.5 years of age (in children, the mean age of onset is 8 years). Late: Presents around 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 Occurs in about 1.5 to 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 in approximately 300,000 persons psoriasis is generalized.

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SEX Equal incidence in males and females.

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

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HEREDITY Polygenic trait. When one parent has psoriasis, 8% of his or her offspring develop psoriasis; when both parents have psoriasis, 41% of their children develop psoriasis. HLA types most frequently associated with psoriasis are HLA- B13, B37, -B57, and, most importantly, HLA-Cw6, which is a candidate for functional involvement.

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TRIGGER FACTORS Physical trauma (rubbing and scratching) is a major factor in eliciting lesions. Acute streptococcal infection precipitates guttate psoriasis. Stress is a factor in flares of psoriasis and is said to be as high as 40% in adults and even higher in children. Drugs: Systemic glucocorticoids, oral lithium, antimalarial drugs, interferon, and β-adrenergic blockers can cause flares 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 resulting in 28 times the normal production of epidermal cells and (2) CD8+ T cells, which are the overwhelming T cell population in lesions. The epidermis and dermis react as an integrated system: the described changes in the germinative layer of the epidermis and inflammatory changes in the dermis, which trigger the epidermal changes. Psoriasis is a T cell–driven disease and the cytokine spectrum is that of a TH1 response. Maintenance of psoriatic lesions is considered ...

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