Psoriasis is a chronic skin condition affecting 2 per cent of the population. From a GP's perspective, it is important to bear this diagnosis in mind when assessing a child with a rash because around 10 per cent of cases present before the age of 10 years and 2 per cent before the age of two years.
Psoriasis is multi-factorial with genetic and environmental factors involved. A child with both parents affected has a 65 per cent lifetime risk of developing psoriasis. This is compared with a 4 per cent lifetime risk if neither parent is affected.
Environmental triggers of psoriasis include streptococcal infection that may trigger guttate psoriasis, stress, trauma (Koebner phenomenon), and drugs. Paediatric psoriasis differs from the adult disease as it is more often attributable to direct precipitating factors.
Clinical types of psoriasis
All clinical types of psoriasis that occur in adults can occur in children, but the most common presentation is chronic plaque psoriasis.
As in adults, lesions typically occur over the extensor surfaces of the limbs. Compared with those in adults, children's lesions are often smaller, thinner and less scaly, which can make diagnosis more difficult.
Facial involvement seems to be more common in children compared with adults and the scalp is often involved. The differential diagnosis of scalp psoriasis includes tinea capitis and seborrhoeic dermatitis.
Flexural psoriasis also occurs in children, and the napkin area is usually first affected. Here there are sharply demarcated erythematous plaques with no scale, often affecting the inguinal folds. The differential diagnoses of napkin psoriasis includes irritant contact dermatitis and seborrhoeic dermatitis.
Guttate psoriasis involves multiple small plaques of psoriasis that develop suddenly, often following a streptococcal infection. It is common practice to treat the streptococcal infection, but evidence suggests that this does not alter the course of the condition.
Guttate psoriatic lesions typically persist for a few months before resolving spontaneously. Guttate psoriasis can recur. The differential diagnoses includes pityriasis rosea and discoid eczema. Erythrodermic and pustular forms of psoriasis are rare in childhood, as is psoriatic arthropathy.
Ensuring concordance with treatment in paediatric patients is a special concern as both the patient and the care-giver require education about the chronic nature of the condition and the need for life-long treatment.
Particularly in younger children, adequate disease control requires a high degree of parental motivation.
For most paediatric patients, topical therapy is sufficient but when it fails, or when there is diagnostic doubt, referral to secondary care is required.
Emollients and calcipotriol
Emollients and soap substitutes should be prescribed in the first instance to relieve scaling and reduce itch.
Calcipotriol is often the first line treatment in children with chronic plaque psoriasis (not recommended in children under six years). It is a vitamin D analogue that affects cell division and differentiation, and has a lesser effect on calcium homeostasis than vitamin D3 itself.
Calcipotriol does not smell or stain and is therefore cosmetically more acceptable than coal tar and dithranol. With doses of less than 50g a week, the risk of metabolic side-effects of calcipotriol is very low.
Topical steroid creams can be used as monotherapy on the face, flexures or palms and soles.
Steroid monotherapy on the body for plaque psoriasis can lead to a recurrence of the disease once the steroid is stopped, so they are used in combination with tars, or a vitamin D analogue such as calcipotriol.
Due to their increased skin to BMI ratio, infants and younger children are at increased risk of systemic side-effects of steroids, including growth retardation, and, with extensive application, suppression of the hypothalamic-pituitary axis.
Children on long-term steroids should have their growth monitored and also have regular check-ups to assess for skin atrophy and systemic side-effects.
Other topical treatment
Coal tar has antimitotic properties and can be used in children for chronic plaque psoriasis. Contact of coal tar with normal skin is not usually harmful so it can be used for widespread small lesions. However, its odour and tendency to stain can affect compliance. Side-effects of coal tar include skin irritation and a sterile folliculitis.
Dithranol is effective for chronic plaque psoriasis, but its major disadvantages are irritation of healthy peri-lesional skin and staining.
Side-effects are minimised by using short contact treatment where the medication is washed off after half an hour. Dithranol is not suitable for widespread small lesions but is effective in the treatment of large thick psoriatic plaques.
Salicylic acid is useful as a keratolytic for thick scaly plaques. On the scalp, it can be used in combination with coal tar or sulphur along with an emollient or oil.
Topical salicylates are not usually used in children under two years and should not be used on large areas of the body because of concerns regarding systemic absorption.
Tazarotene is a topical retinoid for mild to moderate plaque psoriasis and is not recommended for children.
Topical immunomodulators, such as tacrolimus, have been used in adults with facial psoriasis, but in children the evidence base is lacking and treatments are unlicensed.
Phototherapy can be given under specialist supervision to children with moderately severe psoriasis in whom topical treatments have failed. However, its use in children is limited by concerns over carcinogenicity and premature ageing.
Systemic drugs are reserved for only the most refractory cases as cumulative toxicity of treatments given is a concern and long-term safety is an important issue in children.
Drugs used in secondary care include acitretin (a vitamin A derivative), methotrexate, ciclosporin and biological agents.
- Dr Mistry is a GP in north-west London and a clinical assistant in dermatology at Chelsea and Westminster hospital
1. Leman JA, Burden AD. Current Paediatrics 2003; 13 (6): 418-22.
2. American Academy of Dermatology. Guidelines of care for the management of psoriasis and psoriatic arthritis. www.aad.org/research/_doc/Psosection1.pdf
3. Canadian Guidelines for the management of plaque psoriasis. www.dermatology.ca/guidelines/cdnpsoriasisguidelines.pdf
4. Owen CM, Chalmers R, O'Sullivan T et al. Cochrane Database Syst Rev 2000; Issue 2; Art no: CD001976. DOI: 10.1002/14651858.CD001976.