Figure 5: Thick adherent scale on an erythematous background, typical of scalp psoriasis.

You should consider a diagnosis of psoriasis in children presenting with vulvitis, balanitis, and perianal itching. Scalp lesions are especially itchy, as well, and temporary hair loss may occur when the thick adherent scale lifts off the scalp surface (Figure 5). Facial lesions are more clearly demarcated, less itchy, and more annular than eczematous patches.¹ A common site is under the eyes (Figure 6).

Figure 6: In children, the periorbital region is commonly involved.

Guttate psoriasis is a frequent presentation in children. Lesions are smaller than those in typical plaque psoriasis, measuring between 1 and 5 mm in diameter (Figure 7). Onset is often acute, with the development of widespread small scaly lesions. It is important to exclude and, if present, treat an associated streptococcal throat or perianal infection.

Figure 7: Widespread, small (1-5 mm) scaly papules, scattered over the trunk, are often associated with a streptococcal throat or perianal infection.

Palmoplantar involvement may appear as either thick scaling with fissuring or glazed erythema. A clear cutoff at the wrist fold is commonly seen (Figure 8). A rare pustular form also occurs.

Figure 8: Palmoplantar involvement with fissuring, thick scale, erythema, and a sharp cut-off.

Psoriasis in young infants usually presents at 1 or 2 years of age as diaper rash with clear margination and a very bright, often glazed, erythema (Figure 9). The groin folds are involved, in contrast to an irritant dermatitis. Response to treatment aimed at standard diaper dermatitis is poor. These infants often develop more typical forms of psoriasis later.¹ Although the diaper rash looks distressing, the child usually does not experience much discomfort. Sometimes, such a rash is followed by explosive, widespread dissemination of small psoriasis-like lesions onto the trunk and limbs, which can be alarming. This manifestation has recently been defined as psoriatic diaper rash with dissemination and is regarded as a true psoriatic manifestation (Figure 10).¹

Figure 9: Napkin psoriasis with a highly glazed erythematous appearance and sharp margins.

In dark-skinned children, a micropapular form occurs, with 1- to 2-mm papules most evident on the extensor aspects of the limbs. These lesions are usually skin colored until scratching demonstrates the white scale (Figure 11).¹

Figure 10: Napkin psoriasis with widespread dissemination.

Generalized pustular psoriasis is rarely seen in children. Lesions may be strikingly annular. The condition has an explosive onset, with sheets of pustules seen on a bright erythematous background (Figure 12), and is often associated with severe systemic toxicity and high fevers. Generalized pustular psoriasis may be the first presentation of psoriasis and may settle spontaneously in a few weeks, leaving the skin normal. It often recurs, however, with more typical psoriasis eventually developing.

Figure 11: Scaly micropapular lesions seen in a dark-skinned child.

A more common form of pustular psoriasis is acropustulosis, which presents as periungual glazed erythema associated with significant nail dystrophy (Figure 13). Palmoplantar psoriasis can also become pustular.

Figure 12: Pustular psoriasis with sheets of pustules on an erythematous background in a very sick child.

Nail involvement is uncommon in children apart from what is seen in acropustulosis. Presentations include nail-plate pitting, onycholysis, and the "oil drop" sign—yellow staining of the nail (Figure 14).

Figure 13: Glazed erythema, thick scaling, and lakes of pus typical of acropustulosis.

Mucosal involvement is rare. It may include erythematous mucosal patches on oral or genital mucosa, oral erosions, and geographical tongue (annular erythematous lesions with raised white borders showing a migratory pattern).⁶

Figure 14: Periungual glazed erythema with associated significant nail dystrophy.

Some children exhibit features of both eczema and psoriasis. Almost all these children have a history of typical discoid eczema, and most have a family history of both atopic disease and psoriasis.¹

Laboratory tests

Although psoriasis is a clinical diagnosis, lab tests do play a role. The most important test to perform is a bacterial throat or perianal swab. Obtain antistreptolysin-O and antiDNase antibody levels to confirm group A beta-hemolytic streptococcal infection as the trigger for guttate psoriasis.

Differential diagnosis

In the diaper area, psoriasis may be confused with irritant diaper dermatitis. The sharply demarcated edges and confluent bright red color are clues pointing to psoriasis.

Psoriasis has a shinier, darker, redder appearance than seborrheic dermatitis and lacks the yellow scale that may be present with the latter.¹

Always consider the possibility of zinc deficiency in the irritable child with a similar psoriasiform eruption around the mouth.

Scalp psoriasis might be misdiagnosed as tinea capitis or seborrheic dermatitis. Tinea can be excluded by a skin scraping for fungal microscopy and culture. Seborrheic scalp dermatitis is usually a postpubertal disease.

Discoid eczema may be mistaken for body plaque psoriasis, although these lesions are generally itchier than psoriatic plaques and may be exudative.

Candidiasis, tinea corporis, and erythrasma may mimic flexural psoriasis. Culture helps to differentiate these conditions.

General principles of treatment

The clinical course, prognosis, and treatment options should be explained to the child (if he is old enough) and the family. They need to be aware that psoriasis is not infectious and will remit but that, regrettably, no permanent cure is available.

The type of treatment depends on the severity and site of disease as well as the preference of the child and parent. Combination and rotational therapy improve efficacy and reduce the risk of side effects.

Topical therapy

Topical corticosteroids are commonly prescribed and can be effective, but they do have a downside. In our experience, a rebound flare of psoriasis often occurs when a potent steroid is discontinued. And, when topical steroids are used long term in this chronic condition, significant side effects, such as atrophy and striae, are a significant possibility. Hypothalamic-pituitary-adrenal axis suppression, a rare side effect, may follow widespread, prolonged application of a potent topical steroid in infants and young children.⁸

Used judiciously, topical steroids are useful when itch is a problem and for lesions on the face, flexures, and genitalia. The strength of the topical steroid is determined by the site. Moderately potent steroids are often needed for plaques on the scalp, trunk, and limbs. Weaker preparations, such as 1% hydrocortisone, are appropriate for sensitive areas such as the face, ears, flexural areas, and genitalia.

Coal tar preparations. As a rule, childhood psoriasis is better treated with tar preparations (liquor carbonis detergens [LCD]) than with topical steroids. Tars achieve a longer remission, although response to treatment is slower. They are also safer for long-term use and often more effective, and rebound upon discontinuation is less of a problem. The strength used depends on the site and nature of the lesions. We have found that coal tar preparations plus salicylic acid in a cream base, applied twice a day, is very useful for plaque psoriasis.

In the past, the smell of, and staining caused by, tar preparations led to poor adherence. But newer formulations smell much better and stain less.

Tars can be an irritant in infants, or at any age if too high a concentration is used. We overcome this problem by simply asking the family to dilute the concentration by adding more base. For mild scalp involvement, we often recommend the regular use of tar shampoos.

Calcipotriol (vitamin D) can be effective for mild or moderate plaque psoriasis in children, and its safety has been established in this population.^9,10 In a recent systematic review, increased efficacy was noted when calcipotriol and potent topical steroids were both applied once a day.¹¹ This study looked at adult patients only, however.

The most common side effect of calcipotriol is irritation, particularly when used on the face, scalp, and flexures. To prevent hypercalcemia, do not exceed the maximum recommended dosage of 50g/m² /wk.¹⁰

Tazarotene is the only topical retinoid approved for the treatment of psoriasis. Available as a 0.05% and 0.1% gel or cream, tazarotene compares favorably with a mid-potency topical steroid.¹² However, local irritation is a common problem. Early data suggest greater efficacy when combined with topical calcipotriol.¹³ Regrettably, all data regarding efficacy and safety relate to adult patients only.

Phototherapy

Phototherapy in the form of narrow band ultraviolet B (UVB) is useful for children with extensive plaque psoriasis. Only those able to cope with the confines of the phototherapy cabinet are candidates for this treatment.¹⁴ Therapy is given three times a week until lesions clear. It is important that the family be aware of the potential side effect of burning, as well as the long-term consequences of photoaging and carcinogenicity.

Systemic treatment

In children with guttate psoriasis, always seek a focus of streptococcal infection and, if found, prescribe a 10-day course of oral penicillin. Children with an acute flare of psoriasis of any type should also be investigated for infection. Treating streptococcal infection will improve the psoriasis, particularly guttate psoriasis, but only temporarily; there is no evidence that antibiotic therapy alters the natural course of the psoriasis.¹⁵

For children with severe disabling plaque psoriasis that has failed to respond to topical treatment, there are three oral options: acitretin, methotrexate, and cyclosporine. Acitretin, a retinoid, is the most commonly prescribed oral treatment, and can be used as monotherapy or in combination with phototherapy.¹⁶ Because of its teratogenic potential, females of childbearing age must use adequate contraception for a minimum of two years after stopping the medication. The usual dose is 0.5-0.75 mg/kg/day. Routine follow-up investigations (liver function tests, fasting lipid profile) are required at regular intervals. Prolonged treatment should be avoided because of the risk of premature epiphyseal closure and impaired bone growth.¹⁷

There is a paucity of studies detailing the efficacy and safety of methotrexate in the pediatric population—just a few case reports in children suffering from severe disease in whom the treatment was successful.^18,19 Methotrexate is an immunosuppressive medication usually given orally in a once-weekly dose.

Again, only case reports describe cyclosporine in the treatment of pustular psoriasis in children.²⁰ One such report recently showed that it was ineffective in two infants with plaque psoriasis.²¹ This treatment should, therefore, be considered for only the most severe cases that have not responded to other therapies.

Children with generalized pustular psoriasis require hospitalization and close monitoring of fluid and electrolyte balance and for evidence of secondary infection. While awaiting spontaneous recovery, we use wet dressings for symptomatic relief. Topical steroids should be used with great caution because of the high risk of absorption, and strong preparations are contraindicated. Tars should also be avoided. In extremely severe cases, treatment with a retinoid or cyclosporine may be considered.^22,23

Prognosis

Psoriasis is a chronic, relapsing condition. Both child and parent should be made aware that, even though this disease may remit spontaneously or with treatment, recurrences are frequent. The family should realize that treatment is aimed at control, not cure. Fortunately, most children have mild disease that usually responds to topical treatment.

The natural history of childhood-onset psoriasis is unknown. Prolonged remission may follow clearance of lesions, but most patients will require intermittent treatment.¹ Guttate psoriasis generally clears without further problems, but patients may redevelop psoriasis following another streptococcal infection or may gradually develop chronic plaque psoriasis.

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