Papulosquamous disorders
Psoriasis
Introduction
Psoriasis is a chronic, inflammatory papulosquamous disease with an estimated prevalence of 1% in children. Pediatric psoriasis is subdivided into congenital, infantile, and childhood, defined as psoriasis presenting at birth, in the first year of life, and between ages 1 and 18 years, respectively. One-third of all patients develop psoriasis in the first two decades of life. Up to 30% of these patients manifest by age 2 with psoriatic diaper rash. Age of onset may predict disease severity. In a large cohort study of childhood psoriasis, for every year increase in age of onset from birth to 18 years, there was a 10% decrease in risk of moderate–severe disease. Precipitating factors are more common in childhood compared with adult-onset psoriasis. Trauma (via Koebner phenomenon) and infections (pharyngeal and perianal group A streptococci in particular) are frequently implicated in initiation and exacerbation of early-onset psoriasis. Psoriasis arising during the acute and convalescent phases of Kawasaki disease has been reported in infants as young as 3 months.
While psoriasis is diagnosed by the presence of characteristic clinical features, diagnosis in the neonatal and infantile period can be challenging because of clinical overlap with other common papulosquamous eruptions. A skin biopsy may be required to confirm the diagnosis in severe or worrisome cases. Otherwise, tincture of time often illuminates the correct diagnosis as the disease evolves towards more classic features.
Cutaneous findings
Plaque and guttate psoriasis are the most common morphologies observed in children. Individual lesions of typical psoriasis consist of erythematous, well-demarcated plaques with silvery-white scale. Guttate, or ‘drop-like’ psoriasis is an eruption of individual papules and small plaques up to 1 cm in size ( Fig. 16.1 ). Psoriasis in infants offers unique variations of morphology and distribution. For example, annular and serpiginous patterns are common ( Fig. 16.2 ) and involvement of the face and anogenital region is typical ( Fig. 16.3 ). Scale may be imperceptible in psoriasis arising in the diaper area, folds and flexures. The Koebner phenomenon (isomorphic response or psoriasis arising at sites of trauma) is commonly observed and may explain the common distributions of psoriasis in the diaper area, scalp and face of infants, as opposed to adults ( Fig. 16.4 
). Nail changes are present in 10% of infants with psoriasis and may include pitting, onycholysis, oil spots, and subungual hyperkeratosis. Pruritus is common. Box 16.1 summarizes the clinical variants and distributions of psoriasis in children.
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Plaque: most frequent subtype, may be annular/figurate/arcuate/serpiginous
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Guttate
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Eczema–psoriasis overlap (eczematous psoriasis or psoriasiform eczema)
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Papular or follicular
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Scalp: localized or diffuse plaque, pityriasis amiantacea, dermatitis erythema nuchae
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Inverse: face and flexures, intertriginous
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Facial: periorbital, perioral, angular cheilitis
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Nails: pits, oil drops, onycholysis, subungual hyperkeratosis
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Linear/Blaschkoid
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Psoriatic diaper rash with or without dissemination
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Palmoplantar, interdigital web spaces
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Psoriatic arthropathy
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Pustular
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Localized:
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Acrodermatitis continua of Hallopeau (digits and nails)
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Palmoplantar pustulosis
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Plaque psoriasis studded with surface pustules
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Generalized:
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von Zumbusch (more common in infancy)
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Annular variant with peripheral pustules (common in older children)
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Erythrodermic
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Diaper psoriasis.
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 ). 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.
Treatment consists of bland emollients and topical anti-inflammatory agents used in combination. Ointment formulations tend to have greater efficacy and tolerability (i.e., less burning with application) than creams. Effective agents include low to mid-potency topical steroids, topical calcineurin inhibitors, low concentrations of liquor carbonis detergens (3–5% LCD) compounded in either white petrolatum or low potency topical steroid, and topical vitamin D analogs such as calcitriol or calcipotriene.
Erythrodermic psoriasis.
Psoriasis presenting as congenital or neonatal erythroderma is a rare, but documented, presentation. 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. The prognosis is guarded. Evolution over time often results in typical localized psoriatic plaques or the erythroderma may persist. 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.
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 ). 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.
Other entities in the differential diagnosis of pustular psoriasis include: viral, fungal, and bacterial infections; secondarily infected atopic or seborrheic dermatitis; acute generalized exanthematous pustulosis; pityriasis rubra pilaris; scabies; miliaria; acrodermatitis enteropathica; eosinophilic pustular folliculitis; erythema toxicum neonatorum; the pustular leukemoid reaction associated with Trisomy 21; and transient neonatal pustular melanosis.
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.
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. 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. A maternal and family history of psoriasis is often absent in cases of congenital psoriasis.
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. Linear psoriasis must be differentiated from inflammatory linear verrucous epidermal nevi. 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.
Extracutaneous findings of infantile psoriasis
Pustular and erythrodermic psoriasis may be accompanied by systemic signs including fever, chills, irritability, lethargy, dehydration, and fluid and electrolyte imbalance, as discussed previously. Psoriatic arthritis is the most common comorbid association in childhood psoriasis but is infrequent in infants. Nail pitting, dactylitis, and enthesitis may be markers of children at risk for arthritis. There is evidence that children with psoriasis, regardless of severity, are more likely to be overweight or obese and thus at increased risk for related complications. A potential relationship between pediatric psoriasis and the metabolic syndrome requires further investigation. At present, there are no data linking infantile psoriasis with obesity or metabolic syndrome.
Differential diagnosis
The differential diagnosis depends on the specific morphology and distribution. Scalp psoriasis may resemble seborrheic or atopic dermatitis in infants. Tinea capitis more frequently has alopecia or hair breakage and can be distinguished with fungal culture. Plaque and guttate psoriasis must be differentiated from neonatal lupus, pityriasis alba, nummular atopic dermatitis, pityriasis rosea, pityriasis rubra pilaris, and tinea corporis. Atopic dermatitis is usually associated with significantly more pruritus and often with other atopic stigmata or family history. Possible infectious etiologies must be considered in pustular psoriasis. Kawasaki disease may display psoriasis-like eruptions in infants, but has other characteristic features which can aid in diagnosis.
Etiology and pathogenesis
Psoriasis is an immune-mediated inflammatory disease that results in accelerated epidermal cell turnover observed clinically as scaly red plaques. The dysregulated cutaneous immune response is modified by environmental factors in genetically susceptible individuals. Psoriasis following bacterial infections as well as Kawasaki disease suggests the potential pathogenic role of superantigens. A family history of psoriasis is often absent in infantile cases but the rate climbs to 80% in older children. HLA-Cw6 is the major risk allele that confers susceptibility to early-onset psoriasis.
Characteristic histology of plaque psoriasis includes parakeratosis, loss of the granular layer, Munro microabscesses, spongiform pustules of Kogoj and a dermal lymphocytic infiltrate. Pustular psoriasis features intraepidermal subcorneal pustules and a mixed dermal inflammatory infiltrate.
Treatment and prognosis
As a chronic disease, psoriasis is characterized by intermittent exacerbations and spontaneous remissions. The choice of treatment is determined by disease morphology, distribution, severity, comorbidities and patient age. Conservative management with cautious progression to systemic therapies in critical cases is recommended for infantile psoriasis. Topical therapies including bland emollients, corticosteroids, vitamin D analogs, topical calcineurin inhibitors, anthralin and tar-based preparations (liquor carbonis detergens 3–5%) may be tried initially and are often all that is necessary for thin plaque or guttate psoriasis.
Severe or rapidly progressive disease refractory to combination topical therapy may require systemic therapy with retinoids, cyclosporine, methotrexate or conservative doses of narrow band UVB phototherapy. Systemic agents require close clinical and laboratory monitoring. Table 16.1 reviews the various topical therapies and Table 16.2 
the systemic agents available to treat childhood psoriasis. Comprehensive reviews of management principles for pediatric psoriasis have been recently published.
| Medication | Mechanism of action | Clinical utility | Potential adverse effects |
|---|---|---|---|
| Corticosteroids | Anti-inflammatory and antiproliferative | All psoriasis variants; all sites of involvement (vary potency and frequency according to site of application (see text)) | Skin atrophy, striae, secondary infection, systemic absorption and HPA axis suppression if diffuse, prolonged application of potent agents |
| Anthralin (dithranol) | Anti-inflammatory and antiproliferative | Plaque psoriasis Guttate psoriasis Nail psoriasis | Staining, irritation, contact dermatitis. Do not use on face or for erythrodermic or pustular psoriasis |
| Coal tar/LCD a | Largely unknown Enzyme inhibition and antimitotic actions; suppression of DNA synthesis | Plaque psoriasis Guttate psoriasis Inverse psoriasis Palmoplantar psoriasis | Folliculitis, irritant/allergic contact dermatitis, photosensitivity; pustular or erythrodermic reactions if used on acutely inflamed psoriasis. Do not use on inflamed, erythrodermic or generalized pustular psoriasis |
| Calcipotriene Calcipotriol | Stimulates epidermal differentiation and inhibits epidermal proliferation | Plaque psoriasis Guttate psoriasis Nail psoriasis Pustular psoriasis Inverse (calcipotriol) Scalp psoriasis | Irritation, hypercalcemia in excessive dosages |
| Tazarotene | Restores normal epidermal differentiation and proliferation and reduces epidermal inflammation | Thick plaque psoriasis Palmoplantar psoriasis Nail psoriasis | Irritation, teratogenicity (pregnancy category X) |
| Calcineurin inhibitors: Tacrolimus Pimecrolimus | Inhibit production of IL-2 and subsequent T-cell activation/proliferation | Thin plaque psoriasis Guttate psoriasis Facial psoriasis Eyelid psoriasis Intertriginous psoriasis Anogenital psoriasis | Skin stinging and pruritus FDA advises (for dermatitis). Avoid in children <2 years (pimecrolimus and tacrolimus 0.03% and 0.1%); and children <15 years old (tacrolimus 0.1%) |
| Drug | Mechanism of action | Dosing | Baseline | Follow-up | Miscellaneous |
|---|---|---|---|---|---|
| Methotrexate (MTX) | Folic acid analog, inhibits DHFR and interferes with DNA synthesis and effects on T cells | 0.2–0.7 mg/kg per week Start with test dose 1.25–5 mg; then increase by 1.25–5 mg per week until therapeutic effect obtained | CBC/platelets Liver function Renal function Hepatitis A/B/C HIV if at risk | CBC, platelets, liver function 7 days after test dose, then: weekly for 2–4 weeks and after each dose, then every 2 weeks for 1 month and every 2–3 months while on stable doses Renal function every 6–12 months | Liver enzymes transiently rise after MTX dosing; obtain labs 5–7 days after the last dose Liver biopsy: no standard recommendations. Avoid in children with or at risk for liver disease CXR if respiratory symptoms arise |
| Retinoids (acitretin) | Vitamin-A analog, binds to nuclear receptors and affects cellular metabolism, epidermal differentiation and apoptosis | 0.5–1 mg/kg per day | CBC/platelets Liver function Renal function Fasting lipid profile Pregnancy testing if appropriate | Liver function and lipid profile after 1 month of treatment and with dose increases, then every 3 months Monthly pregnancy test (if age appropriate) | Baseline skeletal survey if long-term treatment anticipated: X-rays of all four limbs and spine, repeated yearly or if symptomatic Ophthalmologic examination if symptomatic |
| Cyclosporine | Calcineurin inhibitor, specifically and reversibly inhibits immunocompetent T cells and suppresses proinflammatory cytokines IL-2 and IFNγ | 3–5+ mg/kg per day | Blood pressure × 2 Renal function Urinalysis with micro fasting lipid profile CBC/platelets Liver function Magnesium Potassium Uric acid HIV if at risk | Blood pressure every visit Every 2 weeks for 1–2 months, then monthly: renal function, liver function, lipids, CBC, Mg+, K+, uric acid | Whole-blood CSA trough level if inadequate clinical response or concomitant use of potentially interacting medications. If Cr increases >25% above baseline, reduce dose by 1 mg/kg per day for 2–4 weeks and re-check. Stop CSA if Cr remains >25% above baseline; hold lower dose if level is within 25% of baseline |
| Biologics | |||||
| TNFα inhibitors Etanercept Infliximab Adalimumab | Etanercept: Fully human fusion protein of TNFα receptor II bound to the Fc component of human IgG1 Infliximab/ Adalimumab: monoclonal antibodies bind TNFα | Etanercept: 0.8 mg/kg SC weekly or 0.4 mg/kg BIW Infliximab: 3.3–5 mg/kg IV at weeks 0, 2, 6, then q 7–8 weeks Adalimumab: 24 mg/m 2 SC (max 40 mg) q 2 weeks a | PPD Electrolytes Liver function CBC with differential Hepatitis A/B/C if at risk HIV if at risk Update vaccinations | CBC, liver function every 4–6 months. Liver function more frequently with infliximab PPD annually Other labs/serologies per signs and symptoms | Avoid live and live-attenuated vaccines (e.g., varicella; MMR; oral typhoid; yellow fever; intranasal influenza; herpes zoster; BCG). Vaccinate household contacts prior to treatment initiation |
a Dosing from published experience in patients with juvenile idiopathic arthritis; in two case reports in pediatric psoriasis, dosing was 40 mg q 2 weeks in two adolescent patients.
The prognosis of the various forms of infantile psoriasis is variable and requires further study. A positive family history of psoriasis and initial presentation with guttate morphology may predict more severe plaque psoriasis later in life.
Pityriasis rubra pilaris
Introduction
Pityriasis rubra pilaris (PRP) is a papulosquamous disorder of unknown etiology. The age of onset is bimodal, with peaks in the first and fifth decades of life. Reports of PRP in children less than 2 years old date back to 1905. Griffiths originally classified patients with PRP into five types based on clinical features, age of onset and prognosis. Type I and II are adult-onset forms (classic and atypical, respectively) and types III, IV, and V represent the juvenile-onset spectrum. Each juvenile type of PRP may arise in infancy and early childhood (see Table 16.3 
).
| Type | Clinical features | Notes |
|---|---|---|
| III classic juvenile | May present as erythroderma. Whitish flaky scale on face and scalp. Follicular keratotic papules and scaly red patches spread cephalocaudally; may develop salmon colored erythroderma admixed with foci of normal skin. Most have palmoplantar keratoderma | May present in first few years of life Over time, the follicular component may be lost and lesions appear more like psoriasis Ectropion in severe cases |
| IV circumscribed juvenile | Well-demarcated plaques on elbows, knees, ankles, dorsal hands and feet. Some have palmoplantar keratoderma | Most common in pre-adolescents but can present in first few years of life |
| V atypical juvenile | Follicular hyperkeratosis, erythema and ichthyosiform dermatitis. Sclerodermoid appearance of hands and feet; may develop contractures | May be congenital and familial. May arise in first few years of life |
| Acute post-infectious | Initially resembles superantigen-mediated disease followed by classic features similar to type III | Infants and young children. Follows infection |
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