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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 unknown,
but 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 analogues, retinoids,
tar, anthralin, corticosteroids, phototherapy, and when severe,
methotrexate, retinoids, biologics, or immunosuppressants.
Epidemiology
and Etiology
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 condition can occur at any age. The cause is unknown, but family history is common, suggesting a genetic component in many cases. 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 injury (Koebner's phenomenon), sunburn, HIV, β-hemolytic streptococcal infection, drugs (especially β-blockers, chloroquine , lithium , ACE inhibitors, indomethacin , terbinafine , and interferon-α), emotional stress, and alcohol.
Symptoms and Signs
Lesions are either asymptomatic or mildly 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/or 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. Plaque psoriasis (psoriasis vulgaris or chronic plaque psoriasis) is the most common pattern of psoriasis; lesions are discrete, oval 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. Subtypes exist and are described in Table 1: Psoriasis and Scaling Diseases: Subtypes of Psoriasis .
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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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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 following 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 presentation); 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 ) 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: Can be fatal if untreated due to high-output heart failure
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Pustular psoriasis of the palms and soles
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Gradual onset 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. Cracks or fissures may form in the center or edge of involved areas
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Treatment: Topical corticosteroids of minimal effective potency, with or without 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/or 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 souls 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 upon resolution
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Treatment: Systemic retinoids; calcipotriol
Prognosis: Waxes and wanes
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Arthritis develops in 5 to 30% of patients and can be disabling (see Joint Disorders: Psoriatic Arthritis).
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.
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 largely based on the lesions' effect on the patient's ability to manage the disease.
Treatment
Treatment options are extensive and include emollients, salicylic acid , coal tar , anthralin , corticosteroids, calcipotriol, tazarotene , methotrexate , retinoids, immunosuppressants, immunotherapeutic agents, and 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 bid 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-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 through an unknown effect. 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 ultraviolet (UV) B 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. Systemic corticosteroids may precipitate exacerbations or development of pustular psoriasis and should not be used for any form of psoriasis. Topical corticosteroids are used bid, 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 improve, 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 limits corticosteroid dosage and prevents tachyphylaxis. Topical corticosteroid use is expensive because large quantities (about 1 oz or 30 g) are needed to cover the entire body. 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 used with an occlusive dressing or flurandrenolide tape left on overnight and changed in the morning is effective. Relapse following discontinuation of topical corticosteroids is often faster than with other agents.
Calcipotriol is a topical vitamin D3 analogue that induces normal keratinocyte proliferation and differentiation; it can be used in combination with topical corticosteroids (eg, calcipotriol can be applied on weekdays and corticosteroids on weekends).
Tazarotene is a topical retinoid. It is less effective than corticosteroids as monotherapy but is useful as an adjunct.
Systemic
treatments:
Methotrexate taken orally is the most effective treatment in severe disabling psoriasis, especially severe psoriatic arthritis or widespread erythrodermic or pustular psoriasis unresponsive to topical agents or psoralen-ultraviolet light therapy (PUVA). 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 ( 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 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 produce diffuse idiopathic skeletal hyperostosis (DISH)—see Joint Disorders: Diagnosis.
Cyclosporine is an immunosuppressant that can be used for severe psoriasis. 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, such as hydroxyurea , 6- thioguanine , and mycophenolate mofetil , have narrow safety margins and are reserved for severe, recalcitrant psoriasis.
Immunotherapeutic agents include tumor necrosis factor (TNF)-α inhibitors ( etanercept and infliximab ), alefacept , and efalizumab (biologics—see Biology of the Immune System: Immunotherapeutics). TNF-α inhibitors lead to durable clearing of psoriasis, but their safety profile is still under study. Alefacept is a recombinant human fusion protein composed of the CD2 binding domain of leukocyte function-associated antigen (LFA) type 3 and the Fc portion of human IgG1. Alefacept reduces the number of memory T effector cells without compromising the number of naïve T cells and effectively clears plaques. Efalizumab is a monoclonal antibody that reversibly binds CD11a, a subunit of LFA-1, thereby blocking T-cell migration, binding, and activation.
Light
therapy:
UV light therapy (phototherapy) is typically used in patients with extensive psoriasis. The mechanism of action is unknown, although UVB light reduces DNA synthesis. 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 advanced 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. Less UV light is required when used with oral retinoids (the so-called “re-PUVA” regimen). Narrow-band UVB light is emerging as an effective treatment and does not require psoralens. 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 from chronic use and to circumvent disease resistance. Sequential therapy refers to initial use of potent agents (such as cyclosporine ) to quickly gain control follow by use of agents with a better safety profile.
Mild plaque psoriasis can be treated with emollients, keratolytics, tar, topical corticosteroids, calcipotriol, and/or anthralin alone or in combination. Exposure to sunlight is beneficial, but sunburn can induce exacerbations.
Moderate-severe plaque psoriasis should be treated with topical agents and either phototherapy or oral agents. Immunosuppressants are used for quick, short-term control (eg, in allowing a vacation from other modalities) and for the most severe disease. Immunotherapeutics 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.
Last full review/revision November 2005
Content last modified November 2005
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