There are surprisingly few meaningful studies on the incidence, prognosis and nature of childhood psoriasis. We know little about how likely it is to remit compared with the disease in adults, and this is largely because there is no definitive definition for childhood psoriasis. In many studies, the diagnosis is usually clinical and, therefore, open to interpretation. A recent publication has sought to clarify how to differentiate childhood psoriasis from eczema (Box).4
The earliest sign that a child is destined to suffer from psoriasis is often cradle cap or persistent nappy rash that typically involves the flexures and has a well-defined edge. The term ‘napkin psoriasis’ refers to a psoriatic nappy rash associated with cradle cap, plaques on the trunk and axilla and often a facial rash, particularly on the cheeks.
In children, psoriasis may present with the typical plaques seen in adults (Figure 4a); however, these are usually smaller, thinner and less scaly. Acute guttate psoriasis with eruption of small lesions after a streptococcal throat infection is a frequent presentation. Common presenting sites include the scalp, retroauricular folds, face, flexures and genital areas. Scalp scaling and a persistent retroauricular rash or infra-auricular fissuring are common and often subtle signs. Acral psoriasis with nail dystrophy (Figure 4b) and erythema and scaling of the fingertips may occur, and may involve only one or a few digits. However, the most common nail change is pitting, and is a useful diagnostic clue. Unusual presentations include persistent rashes on the palms and soles (Figure 4c), intertrigo of the hands and feet (Figure 4d), follicular eruptions, persistent angular cheilitis and blepharitis.
Rarely, acute pustular psoriasis may occur in children, with sudden onset of widespread erythema studded with sheets of pustules and associated fever and systemic toxicity. Children with this condition should be admitted to hospital and monitored for systemic infection and evidence of dehydration. Mild topical corticosteroids, wet dressings and oral antibiotics are used for treatment. Recovery may take several weeks.
In some children, psoriasis and atopic dermatitis occur together. This is not surprising, considering how common each is, and recent evidence suggests they may be linked genetically in some patients. When this occurs, typically there are eczematous lesions in the cubital and popliteal fossae, but also psoriatic plaques on the dorsal surface of the elbows, knees and other typical areas such as the scalp. Parents will often relate that the dermatitis component clears easily and promptly with topical corticosteroid, while other lesions are resistant to treatment. Concurrent psoriasis is one of the most common reasons for ‘nonresponsiveness’ in treating atopic dermatitis.
In children a common precipitant of psoriasis is streptococcal throat infections. Stress and trauma may also play a part, as they do in adults.
Psoriasis is an unpredictable, recurrent or chronic condition. It is seldom severe in children, and psoriatic arthritis is very uncommon.
Management of psoriasis in children may vary depending on the site, nature and severity at different stages. It is important that treatment is individualised. Almost all of the topical therapies used for adult psoriasis may be used in children.