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For further information, see CMDT Part 6-11: Psoriasis

Key Features

Essentials of Diagnosis

  • Silvery scales on bright red, well-demarcated plaques, usually on the knees, elbows, and scalp

  • Nail findings include pitting and onycholysis (separation of the nail plate from the bed)

  • Mild itching is common

  • May be associated with psoriatic arthritis

  • Patients with psoriasis are at increased risk for

    • Cardiovascular events

    • Type 2 diabetes mellitus

    • Metabolic syndrome

    • Lymphoma

  • Histopathology is not often useful and can be confusing

General Considerations

  • A common benign, chronic inflammatory skin disease with both a genetic basis and known environmental triggers

  • Injury or irritation of normal skin tends to induce lesions of psoriasis at the site (Koebner phenomenon)

  • Obesity worsens psoriasis, and significant weight loss may lead to substantial improvement

  • Psoriasis has several variants—the most common is the plaque type

Clinical Findings

  • There are often no symptoms, but itching may occur

  • Although psoriasis may occur anywhere, examine the scalp, elbows, knees, palms and soles, umbilicus, and nails

  • The lesions are red, sharply defined plaques covered with silvery scales; the glans penis and vulva may be affected; occasionally, only the flexures (axillae, inguinal areas including genitalia) are involved ("inverse psoriasis")

  • Fine stippling ("pitting") in the nails is highly suggestive

  • Persons with psoriasis often have a pink or red intergluteal fold

  • There may be associated seronegative arthritis, often involving the distal interphalangeal joints

  • Eruptive (guttate) psoriasis consisting of numerous, smaller lesions 3–10 mm in diameter occurs occasionally after streptococcal pharyngitis

Differential Diagnosis

  • Atopic dermatitis (eczema)

  • Contact dermatitis

  • Nummular eczema (discoid eczema, nummular dermatitis)

  • Tinea

  • Candidiasis

  • Intertrigo

  • Seborrheic dermatitis

  • Pityriasis rosea

  • Secondary syphilis

  • Pityriasis rubra pilaris

  • Onychomycosis (nail findings)

  • Cutaneous features of reactive arthritis

  • Cutaneous T cell lymphoma (mycosis fungoides)


Diagnostic Procedures

  • The combination of red plaques with silvery scales on elbows and knees, with scaliness in the scalp or nail findings, is diagnostic

  • Psoriasis lesions are well demarcated and affect extensor surfaces—in contrast to atopic dermatitis, with poorly demarcated plaques in flexural distribution

  • In body folds and groin, scraping and culture for Candida and examination of scalp and nails will distinguish inverse psoriasis from intertrigo and candidiasis


  • Certain drugs, such as β-blockers, antimalarials, statins, lithium and prednisone taper, may flare or worsen psoriasis


  • Topical corticosteroid cream or ointment

    • Restrict a highest-potency corticosteroid to 2–3 weeks of twice daily use; then three or four times on weekends or switch to a midpotency corticosteroid

    • Rarely induces a lasting remission

  • Calcipotriene ointment 0.005% or calcitriol ointment 0.003%, both vitamin D ...

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