Psoriasis in children

Psoriasis is often missed in children. Dr Gayle Fischer advises on its diagnosis and treatment.

PSORIASIS is a very common genetic disorder. Although it is understood that the mechanism of the skin lesions is too-rapid turnover of the epidermis, the exact pathogenesis remains unknown, as does the exact mode of inheritance. Nevertheless we know that psoriasis runs strongly in families.

Psoriasis is usually considered to be a condition with onset in young adulthood, but it can and does present in children from infancy onwards. The prevalence in children is unknown.

The usual figure accepted for the prevalence of psoriasis in the community is about 2%, however this may well be an underestimate. There are two reasons for this.

Firstly, mild cases often go unrecognised. Secondly, psoriasis is a clinical diagnosis. Biopsy is not always diagnostic and often difficult to justify in children.

There exists a spectrum of involvement in psoriasis; it can be a mild condition, which represents nuisance value only, or a disabling disease.

The former is common in children and it is very unusual to see the most severe forms of psoriasis before puberty.

Nevertheless, psoriasis in children severe enough to present to a doctor is often missed clinically, because the usual assumption is that it does not occur in this age group.

Psoriasis has many clinical variants. Some are well recognised in children. These include napkin psoriasis found in infancy and guttate psoriasis, an exanthematic form found in older children after streptococcal throat infection.

In fact, all forms of psoriasis occur in children, but the presentation can be different to the classic presentation in adults.

PSORIASIS IN INFANCY
Before 12 months of age, psoriasis may present as cradle cap or as persistent nappy rash with flexural involvement and a well-demarcated edge.

One-third of babies with seborrhoiec dermatitis go on to develop psoriasis.

Napkin psoriasis is very similar to seborrhoiec dermatitis but is often acute in onset and has typical psoriatic features: well-defined plaques involving the groin, axilla and central face with small, scattered ovoid plaques on the trunk.

Napkin psoriasis may present as persistent
nappy rash with flexural involvement and
a well-demarcated edge.

PSORIASIS IN CHILDHOOD
Guttate psoriasis is the best-known form in this age group.

Typically preceded by an acute streptococcal throat infection, it presents with acute onset of multiple small scaly plaques that may last many weeks if not treated.

Despite this, the commonest form of childhood psoriasis presents with poorly defined, lichenified, scaly plaques on the dorsal surface of the elbows, knees and ankles, and often also the trunk and legs.

There is often also scaling of the scalp as well as scaling, erythema and fissuring in the post- and infra-auricular skin.

It is not uncommon for a moderate degree of atopic eczema to be present as well, with involvement of the cubital and popliteal fossae. The rash may be itchy but usually not as itchy as eczema.

Other presentations in this age group include scalp scaling, anogenital rashes, palmoplantar rashes, angular cheilitis and blepharitis.

Psoriasis in children is often difficult to
distinguish from atopic eczema.

CLUES TO DIAGNOSIS
Most children with psoriasis are initially thought to have eczema.

However, there are characteristics that they tend to have in common which help to differentiate the condition:

• treatment resistance
• scalp scaling
• infra- and post-auricular scaling/splitting
• family history of psoriasis (30%, but rises to 60% if parents are examined)
• nail changes, such as pitting
• history of exacerbation after bacterial throat infection
• history of improvement with sun exposure (parents may see this as improvement with salt water at the beach).

TREATMENT
Psoriasis is a chronic condition that has first to be brought into remission and then kept there with maintenance treatment.

Because it is a hyper-proliferative, rather than an inflammatory condition, it is usually more difficult to treat than eczema, and the environmental modifications and allergy testing often helpful in eczema are less rele­vant. Precipitants in children are most often streptococcal infection and emotional stress.

All of the topical therapy used in adults may be used in children, including tar creams, calcipotriol and dithranol. Judicious sun exposure without sunburn is helpful.

The presence of a high ASOT in a child with guttate psoriasis or with more chronic disease associated with recurrent ENT infections, indicates the need for oral antibiotics and possibly ENT referral in the latter situation. Some children improve markedly after a tonsillectomy.

The more that topical corticosteroids are used, the less effective they are. Nevertheless, they are useful to treat itch, and to initiate treatment prior to using more specific treatment.

It is important to consider three factors:

1. The parent must understand how chronic psoriasis is. The child will tire of constant treatment, and child and parent will have to find strategies to keep it going.
2. Stinging from topical therapy can be a problem that may limit compliance. It can be reduced by the use of ointments rather than creams, use of low-potency tars and pretreatment with cortico­steroids before using specific psoriasis treatments.
3. Parents are often concerned about topical corticosteroid use and need reassurance.

In general it is useful to commence with a regimen similar to that used in eczema treatment, using emollient and topical corticosteroids. Once lesions have become less inflamed and fissuring or excoriation has healed, an attempt should be made to introduce tars and calcipotriol.

It may be months before the skin is back to normal. Maintenance with regular use of tar creams is often effective.

PROGNOSIS
No longitudinal studies exist to determine whether childhood psoriasis remits at puberty. However, the condition is less severe and more responsive to treatment than adult disease. In the short term the prognosis is generally very good.

Dr Gayle Fischer is a paediatric dermatologist at Royal North Shore Hospital, Sydney. Dr Stephen Shumack is honorary secretary of the Australasian College of Dermatologists.