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For further information, see CMDT Part 6-38: Psoriasis
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Essentials of Diagnosis
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Silvery scales on bright red, well-demarcated plaques, usually on the knees, elbows, and scalp
Nails: pitting and onycholysis (separation of the nail plate from the bed)
Mild itching is common
May be associated with psoriatic arthritis
Histopathology is helpful
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General Considerations
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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
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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
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Differential Diagnosis
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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)
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Diagnostic Procedures
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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
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Choice of therapy depends on extent of affected body surface area (BSA) and the presence of other findings (eg. arthritis)
Certain medications, such as β-blockers, antimalarials, statins, lithium, and prednisone taper, may flare or worsen psoriasis
See Table 6–2
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