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Psoriasis

Introduction

Psoriasis is an inflammatory and hyperplastic disease of the skin, characterised by erythema and scale. It is common and affects about 0.5% to 3% of different population groups. It is strongly familial. The presentation is variable and the course frequently difficult to predict. The clinical manifestations are numerous and may range from minor inflammation at one or two sites on the skin to total skin involvement with pustulation and constitutional symptoms. There is an associated arthritis in up to 7% of patients.

Pathogenesis of psoriasis In psoriasis there is increased epidermal proliferation, with greatly increased rate of cell turnover. This increased cell turnover thickens the epidermis and produces excessive and abnormal scaling. There is also vascular proliferation and significant inflammation in the upper dermis. The primary defect may be an abnormally activated immune response in the skin.Psoriasis is polygenically inherited and requires specific environmental factors to become activated. Common trigger factors are infections (streptococcal, viral including human immunodeficiency virus), trauma to the skin (see Koebner phenomenon, psychological stress and drugs.Severe flares of psoriasis, including pustular psoriasis, may be triggered by lithium, beta-blockers, chloroquine, hydroxychloroquine and interferon alfa, and by the withdrawal of systemic and potent topical corticosteroids. Many other drugs (eg angiotensin converting enzyme inhibitors and nonsteroidal anti-inflammatory drugs) have been reported to precipitate or aggravate psoriasis; however, these associations are not always clear.Although the disease may present at any age, there are two peaks of onset: age 16 to 22 years for more severe, therapy-resistant, strongly familial psoriasis; and 57 to 60 years, when family history may be absent and the disease may be milder. The psoriatic process seems to be a complex interaction between keratinocytes and T-lymphocytes. Cytokines and epidermal growth factors cause proliferation and inflammation.

Types of psoriasis

Plaque psoriasis

Plaques are typically raised, pink and surmounted with a silvery scale. Common sites are the elbows, knees, sacrum and scalp. Lesions may be single or numerous, and individual plaques may coalesce into large confluent areas, sometimes 30 cm or more in diameter.

Guttate psoriasis

This term ‘guttate’ derives from the Latin ‘droplet’. Lesions of guttate psoriasis are especially numerous, 2 to 10 mm in diameter, and found on the trunk and proximal limbs. Like plaque psoriasis the lesions are pink, but scaling may be less prominent. Guttate lesions are typically seen in childhood psoriasis and may be triggered by an upper respiratory tract streptococcal infection.

Flexural psoriasis

Flexural psoriasis may involve the groin, gluteal cleft, axillae and submammary folds, without evidence of psoriasis elsewhere. Involvement of the genital or perianal region in isolation may cause diagnostic difficulty, as there is often little scale (see Genital psoriasis).

Erythrodermic psoriasis

Involvement of the entire skin surface may occur from gradual extension of plaque psoriasis, or it may occur as an eruptive phenomenon. The eruptive variant may be accompanied by widespread pustulation (acute generalised pustular psoriasis of von Zumbusch), fever and constitutional symptoms (see Exfoliative dermatitis [erythroderma]). There may be no typical lesions of psoriasis present.The disorder may be resistant to therapy and it may follow a stormy course. Complications include cardiac failure, infections, malabsorption and anaemia.

Palmoplantar psoriasis

Palmoplantar psoriasis can be hyperkeratotic or pustular. Both types may mimic dermatitis but psoriatic manifestations elsewhere can suggest the diagnosis. Trauma may aggravate palmar psoriasis.

Scalp psoriasis

Scalp psoriasis varies from minor scaling with erythema to thick hyperkeratotic plaques covering most of the scalp and extending beyond the hairline. Scratching an irritable scalp causes aggravation via the Koebner phenomenon.

Nail psoriasis

Nail psoriasis is discussed in Nail disorders.

Genital psoriasis

Genital psoriasis is discussed in Genital skin diseases.

Management of psoriasis

Introduction

Psoriasis, in most cases, can be controlled with therapy. It is important that treatment is appropriate for the type and site of psoriasis. In a mild case, emollients or a weak topical corticosteroid may suffice, but disabling or disfiguring psoriasis may warrant the use of systemic drugs such as antimetabolites or immunosuppressants. The treatment of the different types of psoriasis is summarised in Table 1.Complicated cases need specialist care and open lines of communication between the dermatologist, general practitioner and patient need to be maintained, especially during exacerbations.

Treatment of different types of psoriasis (Table 1)

General measures in management of psoriasis

Explain the nature of psoriasis to the patient. Emphasise its benign nature, the rarity of serious associations and the ability of treatments to control the disease in most cases. The psychological effect of psoriasis can be severe and out of proportion to the degree of involvement. Suicidal ideation in patients with chronic psoriasis is not rare.Stress can aggravate the disorder. Consider stress management techniques, exercise and reduction of alcohol intake. Weight reduction will help patients with flexural psoriasis or plantar psoriasis. Special diets have not been proven to help psoriasis.

Antibiotics in management of psoriasis

Psoriasis occasionally becomes infected, usually with Staphylococcus aureus. Flexural psoriasis can become infected with coliforms. Guttate psoriasis may be triggered by an upper respiratory tract streptococcal infection and, if proven, requires treatment with phenoxymethylpenicillin or a suitable alternative (see Pharyngitis and/or tonsillitis).Palmoplantar pustular psoriasis may respond to tetracyclines (which owe their efficacy to their anti-inflammatory effects).

Topical therapy in management of psoriasis Topical therapy must be tailored to individual needs and should take into account the site involved, extent, patient’s age and likely compliance with treatment.

Corticosteroids

Topical corticosteroids are potent inhibitors of cytokine production, resulting in anti-inflammatory and antimitotic effects. They are the most commonly employed agents in therapy of psoriasis. In general terms, the more potent preparations are used to treat thicker areas of skin or thicker plaques of psoriasis. The major adverse effects with the use of topical corticosteroids are skin atrophy, sometimes with the formation of striae, and telangiectasia. These effects are seen most often in the flexures and on the face, and special care is required when using topical corticosteroids in these sensitive areas (see Getting to know your drugs).Patients with widespread disease need increased quantities of these preparations. Full body coverage for an adult male requires approximately 30 g daily of a cream base and slightly less of an ointment base.

Emollients

Where scaling or irritation are prominent features, the soothing action of emollient creams or ointments offers prompt relief. Use

Keratolytics

Both salicylic acid and sulfur are used to lift and soften thick scale in psoriasis. Salicylic acid is more commonly used and is compounded in an ointment or cream base. Use

Tars

Tars are anti-inflammatory and antipruritic. Although these preparations are regarded as first-line therapies, their use is declining because of limited patient acceptability due to their colour and odour. However, they remain one of the most important therapies for psoriasis in children.Liquor picis carbonis (LPC)[Note 1] is the preferred preparation. Use

Salicylic acid 2% to 4% can be included in coal tar preparations.

Dithranol

Dithranol has an antiproliferative effect on psoriatic skin. It is one of the most effective topical agents for psoriasis especially in thick plaque psoriasis. However, it stains both clothes and skin, and can burn unaffected skin (see Difficult to use preparations). Use

Higher concentrations are used in a short-contact regimen. Use

Calcipotriol

Calcipotriol regulates proliferation and differentiation of keratinocytes. It is effective in psoriasis but slow to work. The best results are often not seen for 6 weeks after therapy is initiated. Use

Caution should be observed in treating widespread disease, as using more than 100 g per week can result in hypercalcaemia (see Getting to know your drugs). Adverse effects include erythema and irritation, especially on the face and flexures.Once daily calcipotriol with once daily application of a potent topical corticosteroid can be a useful combination.

Systemic therapy in management of psoriasis When psoriasis is widespread, severe, or causing disfigurement or disability, systemic therapy is indicated. Drugs that have antiproliferative, anti-inflammatory or immunosuppressive effects may be used. Ultraviolet light, with or without photosensitising drugs, may also be useful. Before embarking on systemic therapy in the psoriatic patient, both patient and doctor should have a clear concept of the risk–benefit ratio.

Methotrexate

Methotrexate slows epidermal cell proliferation and is an immunosuppressant. It is the most commonly prescribed oral antipsoriasis drug. It is best used for a few months at a time to limit cumulative toxicity; however, some patients require continuous therapy.The usual dose is

Adverse reactions are more common in the elderly and in patients with reduced renal clearance, and lower doses should be prescribed. Adverse effects include nausea, pancytopenia and elevation of liver enzymes.Nausea may be controlled by the concomitant administration of

Long-term use of methotrexate may induce liver or pulmonary fibrosis. Monitor patients regularly with full blood and liver function tests. Patients on long-term methotrexate therapy require periodic review by a gastroenterologist and may require liver biopsy.Other antimetabolites used occasionally by dermatologists are hydroxyurea and thioguanine.

Acitretin

Acitretin affects mechanisms of proliferation and differentiation and is also anti-inflammatory. It is used in psoriasis in two ways:· as monotherapy in the control of palmoplantar and other hyperkeratotic forms of the disease, as well as pustular, erythrodermic and atypical presentations of psoriasis· to increase the efficacy of phototherapy using narrowband ultraviolet B (UVB) therapy or psoralen and ultraviolet A (PUVA) therapy. As monotherapy, the recommended dose is

Acitretin is teratogenic and pregnancy should be avoided during its use and for 2 years following cessation of therapy. Care must be taken to comply with the provisions of State/Territory law when prescribing acitretin. Other adverse effects of acitretin include all those of hypervitaminosis A: cheilitis, hair fall, photosensitivity, elevated liver enzymes and increased serum lipids.

Cyclosporin

Cyclosporin is an immunosuppressant drug that selectively inhibits activated T-helper cells and reduces the production of cytokines. It is very effective in controlling psoriasis. Use

It does not produce long remissions, and recurrence follows discontinuation. It is not recommended for continuous use because of long-term adverse effects such as hypertension, deterioration of renal function, hirsutism, gingival hyperplasia and development of neoplasia (specifically skin squamous cell carcinoma and lymphoma).

Newer drugs

Drugs which target tumour necrosis factor alpha (eg etanercept) or leucocyte-function–associated antigen (eg alefacept) have shown great promise, but these require parenteral administration and are currently limited to hospital use in Australia.

Phototherapy in the management of psoriasis Ultraviolet light inhibits the function of epidermal Langerhans cells and suppresses cell-mediated immunity. Three forms of phototherapy have been used in psoriasis (see Pertinent practical points).

Narrowband UVB (311 nm)

The adverse effects of this treatment seem to be few. Carcinogenesis has not so far been demonstrated; however, lag times for the development of skin cancer are prolonged. Remission seems to be shorter than seen with psoralen and ultraviolet A (PUVA) therapy, but the lack of long-term problems indicates that it should be the first-line form of phototherapy in most patients.

Broadband UVB (290 to 320 nm)

This is a tried and tested therapy, having been used for more than 80 years. It has not been shown to be carcinogenic. It is often combined with tar therapy for added efficacy.

Psoralen and ultraviolet A (PUVA) (320 to 400 nm)

Ultraviolet A light source is administered following pretreatment with a psoralen drug, usually

Adverse effects include nausea and photosensitivity. Long-term use causes skin atrophy, lentigines and, after cumulative high dose, the incidence of squamous cell carcinoma is greatly increased. Long-term studies are still in progress but it appears to also cause a small but definite increase in melanoma.Both PUVA and narrowband UVB are made more efficacious by pretreatment with acitretin. Continuation of acitretin during a course of phototherapy reduces the cumulative dose needed for clearing the psoriasis and lengthens the duration of post-treatment remissions.

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