Psoriasis

A disorder characterized by well-defined, erythematous plaques covered with a silvery scale.

About 3% of persons with psoriasis first develop the disease after age 60. The cause is unknown, although many drugs, especially -blockers and lithium, can exacerbate the condition.

Symptoms and Signs

Although psoriasis may occur on any area of the body, the usual sites are the extensor surfaces (especially the knees and elbows), scalp, and buttocks. Psoriatic lesions often appear at sites of trauma, such as surgical scars or scratch marks (Koebner's phenomenon). Nail involvement produces pitting, thickening, "oil-spot" discoloration, and onycholysis (separation of the distal edge of the nail plate from the nail bed).

Guttate psoriasis is a variant characterized by small droplike lesions. It is often associated with a streptococcal pharyngitis (and responds to an antistreptococcal antibiotic). Pustular psoriasis, a rare variant, is characterized by sterile pustules that may be localized to the hands and feet or generalized.

Exfoliative dermatitis can occur with psoriasis, particularly after withdrawal of systemic corticosteroids (therefore systemic corticosteroids should be avoided).

Psoriatic arthritis occurs in a small percentage of elderly persons with psoriasis and typically produces fusiform swelling and tenderness of the distal interphalangeal joints. Other types of arthritis (monarthritis, sacroiliitis, and a seronegative arthritis otherwise indistinguishable from rheumatoid arthritis) can also occur.

Treatment

Treatment of limited plaque psoriasis is usually best managed with a topical regimen. Resistive or extensive disease is best managed with more potent oral drugs or with other modalities, such as phototherapy and photochemotherapy.

Topical drugs: Topical corticosteroids may be used alone or with coal tar or anthralin. Initial short-term use of a potent topical corticosteroid ointment, such as betamethasone dipropionate 0.05% or triamcinolone acetonide 0.1%, may be needed. As the psoriatic plaques respond to treatment, the frequency of ointment application should be reduced, substituting emollients, until only emollients are used. For small, localized lesions, flurandrenolide-impregnated tape can be applied and left on overnight or the medication can be covered with plastic wrap to increase potency. Systemic corticosteroids should not be used, in part because their withdrawal may cause a flare-up of the psoriasis, including rebound exfoliative dermatitis or conversion to pustular psoriasis.

Calcipotriene (a vitamin D₃ analog) can be used in combination with corticosteroids. Calcipotriene is available as an ointment, cream (preferred for intertriginous areas), and solution (for the scalp). Rarely, because of systemic absorption, calcipotriene causes hypercalcemia. Alternatively, tazarotene (a topical retinoid) can be used in combination with corticosteroids.

Oral drugs: In elderly patients with disabling psoriasis who cannot use topical drugs or who are unresponsive to other treatments, methotrexate, in oral doses as low as 2.5 mg/week, can control psoriasis. Because methotrexate can be toxic in cumulative doses exceeding 1 to 1.5 g/day, close supervision by a dermatologist is recommended; blood counts and hepatic and renal function must be monitored. After a cumulative dose of 1 to 1.5 g, liver biopsy is recommended.

Cyclosporine, in doses of 3 to 5 mg/kg/day, usually controls psoriasis within 8 weeks. Renal toxicity is the major concern--blood pressure, creatinine, and electrolytes must be monitored monthly. Cyclosporine is contraindicated in patients with a history of malignancy.

Systemic retinoids have been used as monotherapy or in combination with psoralens plus ultraviolet A (PUVA), but none are available in the USA. They (eg, acitretin) are contraindicated in patients with prior hepatic insufficiency. Liver function tests and lipids should be monitored regularly. Long-term adverse effects include hyperostosis.

Phototherapy: Phototherapy with ultraviolet B (UVB) in a whole-body treatment cabinet 3 times/week is highly effective for severe, extensive psoriasis. Phototherapy does not produce the adverse effects associated with frequent topical treatment and treats the entire skin surface, thus discouraging new lesions. Regular sun exposure is often as helpful but requires a favorable climate and appropriate sunbathing facilities (tanning parlors do not provide the correct wavelength of light).

Photochemotherapy: Photochemotherapy with PUVA is also useful for treating severe, extensive psoriasis. Typically, methoxsalen 0.6 mg/kg is taken orally 2 hours before exposure to UVA. Topical psoralens can also be combined with UVA for resistant localized disease (eg, palmoplantar involvement) but with a higher risk of severe burns.