In children younger than 2 years of age, psoriatic diaper rash is a common presentation (see also Chapter 17). It presents as bright red, glazed appearing, well-marginated individual or confluent plaques with absent or minimal scale, involving the anogenital area including skin folds. It often expands toward the abdomen and thighs where the scale becomes more perceptible (Fig. 16.5). In some cases, there is widespread dissemination of the psoriasis shortly after the diaper eruption appears, referred to as psoriatic diaper rash with dissemination or as diaper dermatitis with psoriasiform id reaction (Fig. 16.6).⁸ Psoriasis and other acute diaper rashes, such as Candida, may result in a psoriasiform id reaction (Fig. 16.7). The initial stages of diaper (‘napkin’) psoriasis are easily confused with other diaper rashes, including irritant dermatitis (which typically spares the folds), Candida infection, seborrheic dermatitis as well as other causes. Infants with diaper psoriasis with dissemination of lesions to other areas of the body and a positive first-degree family history of psoriasis are probably at greatest risk for developing typical psoriasis later in life.^9–11

Psoriasis presenting as congenital or neonatal erythroderma is a rare, but documented, presentation.^12,13 Neonatal erythrodermic psoriasis has overlapping features with primary immunodeficiency syndromes, Netherton syndrome, metabolic disorders, systemic infections, and certain forms of ichthyosis. A positive family history of psoriasis, patchy rather than diffuse involvement, and absence of other features of ichthyosis (e.g., ectropion and eclabium) may help to differentiate psoriasis from ichthyosis in early life.¹⁴ The prognosis is guarded. Evolution over time often results in typical localized psoriatic plaques or the erythroderma may persist.¹² This presentation is also potentially life-threatening. The impaired skin barrier confers a risk of hyperpyrexia, hypernatremic dehydration, hypoalbuminemia, septicemia, and cutaneous infections. Management consists of optimized nutritional status and fluid and electrolyte balance. Control of inflammation with topical steroids and barrier reinforcement with bland emollients to prevent further metabolic disarray and infections is imperative.

Pustular psoriasis.

Pustular psoriasis in infancy may be localized or generalized. Generalized pustular psoriasis of von Zumbusch (GPP) is characterized by fever and an explosive eruption of sheets of sterile pustules on inflamed skin (Fig. 16.8). The pustules may be arranged at the periphery of annular or serpiginous plaques (Fig. 16.9). Annular pustular psoriasis, alone or together with generalized pustulation, is the most common form observed in children. Affected children may appear well or exhibit systemic symptoms of progressive malaise, lethargy, irritability and unwillingness to eat. GPP runs an unpredictable course with relapses and remissions. Severe, localized pustular psoriasis of the nail unit (acrodermatitis continua of Hallopeau) may occur in isolation or accompany generalized pustular psoriasis.

Pustular psoriasis localized to the intertriginous areas, particularly the neck, is a relatively uncommon subtype that may be misdiagnosed as bacterial or candidal intertrigo. Affected infants are often 1–2 months old and otherwise well. There may be a positive family history of psoriasis. This localized intertriginous variant may progress to widespread disease requiring systemic therapy.¹⁵

The differential diagnosis of neonatal and infantile pustulosis includes a recently described rare condition, ‘deficiency of interleukin 1 receptor antagonist’ (DIRA). DIRA is an autosomal recessive, early-onset, life-threatening autoinflammatory syndrome primarily affecting the skin and bones. Patients typically present as neonates or young infants with a localized or generalized pustular eruption, desquamation, multifocal osteomyelitis and periostitis, failure to thrive, and elevated inflammatory markers (Fig. 16.10).¹⁶ DIRA is mediated by mutations in the IL1RN gene encoding the interleukin 1 (IL-1) receptor antagonist, resulting in unopposed, widespread systemic inflammation. The allele frequencies of the causative mutations are highest in patients from Puerto Rico, the Netherlands, and Newfoundland. IL1RN gene sequencing is diagnostic. These patients require targeted therapy with the recombinant human IL-1 receptor antagonist, anakinra.^16,17

The treatment of GPP varies. Milder cases can be controlled with topical corticosteroids and vitamin D analogs. Severe cases may require hospitalization for work-up, supportive care and initiation of systemic therapy. Cultures should be obtained from pustular lesions, and if repeatedly sterile, should alert physicians to the diagnosis of pustular psoriasis. Oral retinoids, cyclosporine, methotrexate and phototherapy comprise the most commonly used and effective agents for severe, refractory or multiply-relapsed pustular psoriasis. Older children with disease refractory to traditional systemic medications may respond to anti-TNF therapy.¹⁸

Congenital psoriasis.

Psoriasis presenting at birth is very rare. Only nine published cases of congenital psoriasis are diagnostically convincing. Of those, plaque, erythrodermic and pustular were the most common clinical subtypes observed. Although no consistent anatomic distribution has been distinguished, the scalp, face, extremities and trunk are commonly involved. Notably, the diaper area is frequently spared, perhaps due to lack of trauma from diapers.¹⁹ Histologically confirmed congenital psoriasis occurring along Blaschko’s lines has been reported. Females are more frequently affected with Blaschko-linear psoriasis presumably due to functional X-chromosome mosaicism.²⁰ A maternal and family history of psoriasis is often absent in cases of congenital psoriasis.¹⁹

The differential diagnosis of congenital psoriasis depends on the presentation. Erythrodermic and papulosquamous cases should be distinguished from seborrheic dermatitis, including localized ‘cradle cap’, congenital or neonatal candidiasis, immunodeficiency syndromes, congenital ichthyosis and Netherton syndrome.²¹ Linear psoriasis must be differentiated from inflammatory linear verrucous epidermal nevi.²² The differential diagnosis for congenital pustular psoriasis includes: bacterial infections; candidiasis; erythema toxicum neonatorum; pustular leukemoid reaction in children with Trisomy 21; transient neonatal pustular melanosis; Langerhans’ cell histiocytosis; and deficiency of interleukin 1 receptor antagonist (DIRA, see above). Alternatively, congenital psoriasis should always be considered in the differential diagnosis of newborns with erythroderma, or papulosquamous or pustular eruptions.

Treatment for congenital psoriasis should be conservative initially with bland emollients and topical steroids. A ‘soak and seal’ regimen using wet wraps with low potency topical steroids can enhance efficacy. Systemic therapy with acitretin or methotrexate is required in some cases. Response to therapy is variable and depends on disease severity.

Long-term prognosis of congenital psoriasis is unknown because follow-up is unavailable for most cases. Infants with presumed pustular psoriasis, failure to thrive, skeletal anomalies and systemic symptoms who are refractory to therapy should be evaluated for DIRA.