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 in obese persons 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 as is onycholysis

• 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 myriad 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)

Diagnosis

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

Treatment

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

• Never use systemic corticosteroids to treat flares of psoriasis

Medications

• See Table 6–2

LIMITED DISEASE (< 10% OF THE BODY SURFACE)

• 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 ...