Psoriasis is a common chronic inflammatory skin condition; it is characterised by dry, raised, silvery or red scaly plaques and often follows an unpredictable pattern of exacerbations and remissions. The plaques form as the skin regenerates far quicker than in normal skin (4 days compared with 28 days for normal skin).

The erythema is caused by the capillaries in the dermal layer dilating. This is generally initiated by T cells or antigen presenting cells. The areas most commonly affected are scalp, sacrum, nails, knees and elbows; but psoriasis can affect any area.

The average age of onset of psoriasis is about 33 years, and is equally prevalent in both men and women. Type 1 psoriasis generally begins when the patient is in their 30s, type 2 occurs when patients are in their 40s or 50s. Psoriasis generally declines in those in their 70s.

Psoriasis is found in people with a family history of it, but often it is triggered by factors such as stress or illness. Lifestyle factors such as smoking, poor diet or alcohol consumption can exacerbate psoriasis. Exposure to sunlight can improve it, or can exacerbate it depending on the patient. ACE inhibitors, NSAIDs and some anti-malarials can also make it worse.

There are several types of psoriasis; these include (flexural or inverse psoriasis (affects the flexure of the axillae or knees, generally less scaly than plaque psoriasis), chronic plaque psoriasis (also termed psoriasis vulgaris. This involves red plaques with white scales, normally found on the extensor surfaces of elbows and knees. Sometimes it affects the scalp and occasionally the lumbar region and umbilicus), guttate psoriasis (red scaly papules, many patients with this type of psoriasis will eventually develop chronic plaque psoriasis in time), facial psoriasis (as it implies, but has the most effect on body image), scalp psoriasis (affects the skin within the hairline, often affects the entire scalp), erythrodermic psoriasis (widespread overage, at least 90% of the skin, often connected with systemic illness), palmar-plantar psoriasis (affects the palms or soles), pustular psoriasis (characterised by widespread erythema and sterile pustules).

Psoriasis patients may also be affected by nail disease (this affects around half of patients with psoriasis), and psoriatic arthritis (affects around 30% of psoriasis patients), other co-morbidities may include ankylosing spondylitis and IBD.

Generally GP consultations for psoriasis are referred for specialist treatment, often in nurse-led clinics. As there is no cure for psoriasis, symptom control is the only option. Emollients are the baseline treatment and are used to reduce irritation, moisturise and soften skin scales. Topical therapy may be employed, this is for applications to small areas and includes preparations of corticosteroids, retinoids (vitamin A analogues), and keratolytics. If phototherapy is ineffective or does not provide sufficient relief from symptoms, phototherapy may be employed. This is the application of UVA or UVB light, although this comes with the side affect of increasing the risk of developing squamous cell carcinoma. Systemic therapy may also be employed with the use of drugs such as methotrexate, fumaric acid esters (not currently licensed, but available in some specialist centres), acitretin and ciclosporin. Methotrexate has the added benefits of being suitable for long-term use and effective in the treatment of psoriatic arthritis. Occasionally biologic therapy may be used such as adalimumab, infliximab, ustekinumab and etanercept. These are given either subcutaneously or IV (infliximab); but their use is restricted due to cost.

Although there are therefore many different treatment options for psoriasis, currently there is no cure, so symptom control is the aim.

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