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Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Cause is unclear but seems to involve the immune system. Common triggers include trauma, infection, and certain drugs. Symptoms are usually minimal with occasional mild itching, but cosmetic implications may be major. Some people develop severe disease with painful arthritis. Diagnosis is based on appearance and distribution of lesions. Treatment is with emollients, vitamin D analogs, retinoids, tar, anthralin, corticosteroids, phototherapy, and, when severe, methotrexate, retinoids, immunomodulatory agents (biologics), or immunosuppressants.
Psoriasis is hyperproliferation of epidermal keratinocytes combined with inflammation of the epidermis and dermis. It affects about 1 to 5% of the population worldwide; light-skinned people are at greater risk. Peak onset is roughly bimodal, most often at ages 16 to 22 and at ages 57 to 60, but the disorder can occur at any age.
Etiology
The cause is unclear but involves immune stimulation of epidermal keratinocytes; T cells seem to play a central role. Family history is common, and certain genes and HLA antigens (Cw6, B13, B17) are associated with psoriasis. An environmental trigger is thought to evoke an inflammatory response and subsequent hyperproliferation of keratinocytes.
Well-identified triggers include
Symptoms and Signs
Lesions are either asymptomatic or pruritic and are most often localized on the scalp, extensor surfaces of the elbows and knees, sacrum, buttocks, and penis. The nails, eyebrows, axillae, umbilicus, and perianal region may also be affected. The disease can be widespread, involving confluent areas of skin extending between these regions. Lesions differ in appearance depending on type.
Among the various subtypes (see Table 1: Psoriasis and Scaling Diseases: Subtypes of Psoriasis ), plaque psoriasis (psoriasis vulgaris or chronic plaque psoriasis) is the most common pattern; lesions are discrete, erythematous papules or plaques covered with thick, silvery, shiny scales. Lesions appear gradually and remit and recur either spontaneously or with appearance and resolution of triggers.
Arthritis develops in 5 to 30% of patients and can be disabling (see Joint Disorders: Psoriatic Arthritis); joint destruction may ultimately occur.
Psoriasis is rarely life-threatening but can affect a patient's self-image. Besides image, the sheer amount of time required to treat extensive skin or scalp lesions and to maintain clothing and bedding may adversely affect quality of life.
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Table 1
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| Subtypes of Psoriasis |
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Subtype
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Description
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Treatment and Prognosis
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Plaque psoriasis
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Gradual appearance of discrete, erythematous papules or plaques covered with thick, silvery, shiny scales
Lesions that remit and recur spontaneously or with appearance and resolution of triggers
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Treatment: Topical corticosteroids of minimal effective potency, with or without vitamin D3 analogs (eg, calcipotriol)
Prognosis: Waxes and wanes
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Guttate psoriasis
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Abrupt appearance of multiple plaques 0.5 to 1.5 cm in diameter, usually on the trunk in children and young adults after streptococcal pharyngitis
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Treatment: Antibiotics for underlying streptococcal infection
Prognosis: Excellent, often with permanent cure
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Erythrodermic psoriasis
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Gradual or sudden onset of diffuse erythema, usually in patients with plaque psoriasis (though may be the first manifestation); typical psoriatic plaques are less prominent or absent
Most commonly caused by inappropriate use of topical or systemic corticosteroids or light therapy
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Treatment: Potent systemic drugs (eg methotrexate, cyclosporine, TNF-α inhibitor) or intense inpatient topical therapy
Tars, anthralin, and phototherapy are likely to exacerbate the condition
Prognosis: Good with elimination of triggering factors
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Generalized pustular psoriasis
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Explosive onset of widespread erythema and sterile pustules
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Treatment: Systemic retinoids
Prognosis: If untreated, can be fatal due to high-output heart failure
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Pustular psoriasis of the palms and soles
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Gradual appearance of deep pustules on palms and soles
Flare-ups may be painful and disabling
Typical psoriatic lesions may be absent
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Treatment: Systemic retinoids
Prognosis: Waxes and wanes
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Inverse psoriasis
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Psoriasis of inguinal, gluteal, axillary, inframammary, and retroauricular folds and of the glans of the uncircumcised penis
Possibly formation of cracks or fissures in the center or edge of involved areas
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Treatment: Topical corticosteroids of minimal effective potency, with or without vitamin D3 analogs (eg, calcipotriol)
Tar and anthralin may be irritating
Prognosis: Waxes and wanes
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Nail psoriasis
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Pitting, stippling, fraying, discoloration (oil spot sign), and thickening of the nails, with or without separation of the nail plate (onycholysis)
May resemble a fungal nail infection
Affects 30–50% of patients with other forms of psoriasis
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Treatment: Responds best to systemic therapy
Brave or stoic patients may respond to intralesional injection with corticosteroids
Prognosis: Often unresponsive to treatment
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Acrodermatitis continua of Hallopeau
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Pustular psoriasis confined to distal fingers or toes, sometimes just one digit
Replaced by scale and crust on resolution
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Treatment: Systemic retinoids
Vitamin D3 analogs (eg, calcipotriol)
Prognosis: Waxes and wanes
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Diagnosis
Diagnosis is most often by clinical appearance and distribution of lesions. Differential diagnosis includes seborrheic dermatitis, dermatophytoses, cutaneous lupus erythematosus, eczema, lichen planus, pityriasis rosea, squamous cell carcinoma in situ (Bowen's disease, especially when on the trunk), lichen simplex chronicus, and secondary syphilis. Biopsy is rarely necessary and may not be diagnostic.
Disease is graded as mild, moderate, or severe based on the body surface area affected and how the lesions affect patients' quality of life. There are many more complex scoring systems for disease severity (eg, the Psoriasis Area and Severity Index), but these systems are useful mainly in research protocols.
Treatment
Treatment options are extensive and include emollients, salicylic acid, coal tar, anthralin, corticosteroids, vitamin D3 analogs, methotrexate, topical and oral retinoids, topical and oral calcineurin inhibitors, immunosuppressants, immunomodulatory agents (biologics), and ultraviolet light therapy.
Topical treatments:
Emollients include emollient creams, ointments, petrolatum, paraffin, and even hydrogenated vegetable (cooking) oils. They reduce scaling and are most effective when applied twice daily and immediately after bathing. Lesions may appear redder as scaling decreases or becomes more transparent. Emollients are safe and should probably always be used for mild to moderate plaque psoriasis.
Salicylic acid is a keratinolytic that softens scales, facilitates their removal, and increases absorption of other topical agents. It is especially useful as a component of scalp treatments; scalp scale can be quite thick.
Coal tar ointments, solutions, or shampoos are anti-inflammatory and decrease keratinocyte hyperproliferation via an unknown mechanism. They are typically applied at night and washed off in the morning. They can be used in combination with topical corticosteroids or with exposure to natural or artificial broad-band UVB light (280 to 320 nm) in slowly increasing increments (Goeckerman regimen).
Anthralin is a topical antiproliferative, anti-inflammatory agent. Its mechanism is unknown. Effective dose is 0.1% cream or ointment increased to 1% as tolerated. Anthralin may be irritating and should be used with caution in intertriginous areas; it also stains. Irritation and staining can be avoided by washing off the anthralin 20 to 30 min after application. Using a liposome-encapsulated preparation may also avoid some disadvantages of anthralin.
Corticosteroids are usually used topically but may be injected into small or recalcitrant lesions. (Caution: Systemic corticosteroids may precipitate exacerbations or development of pustular psoriasis and should not be used to treat psoriasis.) Topical corticosteroids are used twice daily, sometimes with anthralin or coal tar applied at bedtime. Corticosteroids are most effective when used overnight under occlusive polyethylene coverings or incorporated into tape; a corticosteroid cream is applied without occlusion during the day. Corticosteroid potency (see Principles of Topical Dermatologic Therapy: Anti-inflammatory agents) is selected according to the extent of involvement. As lesions abate, the corticosteroid should be applied less frequently or at a lower potency to minimize local atrophy, striae formation, and telangiectases. Ideally, after about 3 wk, an emollient should be substituted for the corticosteroid for 1 to 2 wk (as a rest period); this substitution limits corticosteroid dosage and prevents tachyphylaxis. Topical corticosteroid use can be expensive because large quantities (about 1 oz or 30 g) are needed for each application when a large body surface area is affected. Topical corticosteroids applied for long duration to large areas of the body may cause systemic effects and exacerbate psoriasis. For small, thick, localized, or recalcitrant lesions, high-potency corticosteroids are used with an occlusive dressing or flurandrenolide tape; these dressings are left on overnight and changed in the morning. Relapse after topical corticosteroids are stopped is often faster than with other agents.
Vitamin D3 analogs (eg, calcipotriol, calcitriol) are topical vitamin D analogs that induce normal keratinocyte proliferation and differentiation; they can be used alone or in combination with topical corticosteroids. Some clinicians have patients apply calcipotriol on weekdays and corticosteroids on weekends.
Calcineurin inhibitors (eg, tacrolimus, pimecrolimus) are available in topical form and are generally well-tolerated. They are not as effective as corticosteroids but may avoid the complications of corticosteroids when treating facial and intertriginous psoriasis. They may be associated with an increased risk of lymphoma and skin cancer.
Tazarotene is a topical retinoid. It is less effective than corticosteroids as monotherapy but is a useful adjunct.
Systemic treatments:
Methotrexate taken orally is the most effective treatment for severe disabling psoriasis, especially severe psoriatic arthritis or widespread erythrodermic or pustular psoriasis unresponsive to topical agents or psoralen plus ultraviolet A (PUVA) light therapy. Methotrexate seems to interfere with the rapid proliferation of epidermal cells. Hematologic, renal, and hepatic function should be monitored. Dosage regimens vary, so only physicians experienced in its use for psoriasis should undertake methotrexate therapy.
Systemic retinoids (eg, acitretin, isotretinoin) may be effective for severe and recalcitrant cases of psoriasis vulgaris, pustular psoriasis (in which isotretinoin may be preferred), and hyperkeratotic palmoplantar psoriasis. Because of the teratogenic potential and long-term retention of acitretin in the body, women who use it must not be pregnant and should be warned against becoming pregnant for at least 2 yr after treatment ends. Pregnancy restrictions also apply to isotretinoin, but the agent is not retained in the body beyond 1 mo. Long-term treatment may cause diffuse idiopathic skeletal hyperostosis (DISH—see Joint Disorders: Diagnosis).
Immunosuppressants can be used for severe psoriasis. Cyclosporine is a commonly used immunosuppressant. It should be limited to courses of several months (rarely, up to 1 yr) and alternated with other therapies. Its effect on the kidneys and potential long-term effects on the immune system preclude more liberal use. Other immunosuppressants (eg, hydroxyurea, 6-thioguanine, mycophenolate mofetil) have narrow safety margins and are reserved for severe, recalcitrant psoriasis.
Immunomodulatory agents (biologics—see Biology of the Immune System: Immunotherapeutics) include tumor necrosis factor (TNF)-α inhibitors (etanercept, adalimumab, infliximab) and the T-cell modulator alefacept. TNF-α inhibitors lead to clearing of psoriasis, but their safety profile is still under study. Efalizumab is no longer available in the US due to increased risk of progressive multifocal leukoencephalopathy.
Phototherapy:
UV light therapy is typically used in patients with extensive psoriasis. The mechanism of action is unknown, although UVB light reduces DNA synthesis and can induce mild systemic immunosuppression. In PUVA, oral methoxypsoralen, a photosensitizer, is followed by exposure to long-wave UVA light (330 to 360 nm). PUVA has an antiproliferative effect and also helps to normalize keratinocyte differentiation. Doses of light are started low and increased as tolerated. Severe burns can result if the dose of drug or UVA is too high. Although the treatment is less messy than topical treatment and may produce remissions lasting several months, repeated treatments may increase the incidence of UV-induced skin cancer and melanoma. Less UV light is required when used with oral retinoids (the so-called re-PUVA regimen). Narrow-band UVB light (311 to 312 nm) used without psoralens is similar in effectiveness to PUVA. Excimer laser therapy is a type of phototherapy using extremely pure wavelengths.
Choice of therapy:
Choice of specific agents and combinations requires close cooperation with the patient, always keeping in mind the untoward effects of the treatments. There is no single ideal combination or sequence of agents, but treatment should be kept as simple as possible. Monotherapy is preferred, but combination therapy is the norm. Rotational therapy refers to the substitution of one therapy for another after 1 to 2 yr to reduce the adverse effects caused by chronic use and to circumvent disease resistance. Sequential therapy refers to initial use of potent agents (eg, cyclosporine) to quickly gain control followed by use of agents with a better safety profile.
Mild plaque psoriasis can be treated with emollients, keratolytics, tar, topical corticosteroids, vitamin D3 analogs, or anthralin alone or in combination. Exposure to sunlight is beneficial, but sunburn can induce exacerbations.
Moderate to severe plaque psoriasis should be treated with topical agents and either phototherapy or systemic agents. Immunosuppressants are used for quick, short-term control (eg, in allowing a break from other modalities) and for the most severe disease. Immunomodulatory agents (biologics) are used for moderate to severe disease unresponsive to other agents.
Scalp plaques are notoriously difficult to treat because they resist systemic therapy, and because hair blocks application of topical agents and scale removal and shields skin from UV light. A suspension of 10% salicylic acid in mineral oil may be rubbed into the scalp at bedtime manually or with a toothbrush, covered with a shower cap (to enhance penetration and avoid messiness), and washed out the next morning with a tar (or other) shampoo. More cosmetically acceptable corticosteroid solutions can be applied to the scalp during the day. These treatments are continued until the desired clinical response is achieved. Resistant skin or scalp patches may respond to local superficial intralesional injection of triamcinolone acetonide suspension diluted with saline to 2.5 or 5 mg/mL, depending on the size and severity of the lesion. Injections may cause local atrophy, which is usually reversible.
Special treatment needs for subtypes are described in Table 1: Psoriasis and Scaling Diseases: Subtypes of Psoriasis.
For psoriatic arthritis, treatment with systemic therapy is important to prevent joint destruction; methotrexate or a TNF-α inhibitor may be effective.
Last full review/revision August 2009 by Peter C. Schalock, MD
Content last modified August 2009
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