Residency · Residency · Dermatology

Common Pediatric Papulosquamous Disorders

Introduction

Papulosquamous disorders are characterized by scaly papules and plaques arising from abnormal epidermal differentiation or inflammation. In children, these conditions present with unique features that often differ from their adult counterparts, requiring age-specific diagnostic and management considerations. This lecture covers psoriasis, pityriasis rosea, pityriasis lichenoides, and lichen striatus in the pediatric population.

Pediatric Psoriasis

Epidemiology

Psoriasis affects approximately 1% of children under age 18, and one-third of adult psoriasis patients had onset before age 16. There is a strong genetic component, with HLA-Cw6 serving as the major susceptibility allele for early-onset psoriasis. Pediatric psoriasis is associated with higher rates of obesity, metabolic syndrome, depression, and anxiety compared to age-matched controls.

Clinical Subtypes in Children

Plaque Psoriasis

Plaque psoriasis is the most common subtype, accounting for 70 to 80% of cases. It presents as well-demarcated, erythematous plaques with silvery-white micaceous scale. In children, plaques are often thinner and smaller than in adults, and scale may be less prominent. Facial involvement is more common in children than adults, occurring in up to 50%. Diaper psoriasis in infants presents as well-demarcated, glazed erythema in the diaper area with minimal scale due to occlusion, and is often the first presentation of psoriasis.

Guttate Psoriasis

Guttate psoriasis is an acute eruption of small (1 to 10 mm), drop-like, salmon-pink papules with fine scale over the trunk and proximal extremities. The classic presentation occurs 2 to 3 weeks after Group A streptococcal pharyngitis. It is self-limited in many children, resolving within 3 to 4 months, but one-third progress to chronic plaque psoriasis. A throat culture or rapid strep test and ASO titers should be obtained, and confirmed streptococcal infection should be treated.

Other Subtypes

Inverse psoriasis features erythematous, smooth, shiny plaques in flexural areas and is often misdiagnosed as a fungal infection. Scalp psoriasis produces thick, adherent scale that may extend beyond the hairline, in contrast to seborrheic dermatitis, which is typically confined within it. Nail psoriasis presents with pitting, onycholysis, oil-drop discoloration, and subungual hyperkeratosis, affecting 40% of pediatric psoriasis patients. Pustular psoriasis is rare in children, with annular pustular psoriasis being the most common pediatric variant.

Management of Pediatric Psoriasis

Topical therapy is first-line for mild-to-moderate disease. Low-to-mid potency TCS are used for the face and intertriginous areas, while mid-to-high potency formulations are used for the trunk and extremities. Calcipotriol (vitamin D analog) may be used alone or in combination with betamethasone dipropionate, and topical calcineurin inhibitors are appropriate for facial and genital psoriasis. Phototherapy with NB-UVB is safe and effective in children for widespread disease. For moderate-to-severe or recalcitrant disease, systemic therapy is indicated. Methotrexate (0.2 to 0.4 mg/kg/week) is the most commonly used traditional systemic agent, with monitoring for hepatotoxicity and bone marrow suppression. Biologics including etanercept (age 4+), adalimumab (age 4+), ustekinumab (age 6+), ixekizumab (age 6+), and secukinumab (age 6+) are increasingly used as first-line systemic therapy given their superior efficacy and safety profiles.

<image>Clinical montage showing pediatric psoriasis subtypes: plaque psoriasis on the knee with silvery scale, guttate psoriasis with widespread small papules on the trunk, and diaper psoriasis with well-demarcated glazed erythema</image>

Pityriasis Rosea

Overview

Pityriasis rosea is a self-limited, acute papulosquamous eruption primarily affecting children and young adults (ages 10 to 35). There is strong evidence for an association with HHV-6 and HHV-7 reactivation. The eruption typically resolves spontaneously within 6 to 8 weeks, occasionally up to 12 weeks.

Clinical Features

The eruption begins with a herald patch, a solitary, oval, 2 to 5 cm pink plaque with central clearing and peripheral collarette scale, which precedes the generalized eruption by 1 to 2 weeks. The secondary eruption consists of smaller, oval, salmon-colored patches following the "Christmas tree" pattern along skin tension lines (Langer's lines) on the trunk. The collarette (trailing) scale is attached at the periphery with the free edge pointing inward. In darker skin tones, the eruption may present as inverse pityriasis rosea (predominantly involving the extremities and face) or with papular morphology. It is usually asymptomatic or mildly pruritic.

Differential Diagnosis

Secondary syphilis must always be considered and tested (RPR/VDRL) in sexually active adolescents, with mucosal patches and condylomata lata serving as distinguishing features. Tinea corporis should be excluded with a KOH preparation. Guttate psoriasis presents with thicker scale and extensor predominance, often following streptococcal infection. A drug eruption should be considered if the distribution is atypical or lesions persist beyond 12 weeks.

Management

Most patients require only reassurance and observation. Topical corticosteroids and oral antihistamines may be used for symptomatic pruritus. Erythromycin and acyclovir have shown some efficacy in shortening disease duration in limited studies but are not routinely recommended. NB-UVB or natural sunlight exposure may accelerate resolution. Post-inflammatory hypo- or hyperpigmentation is common in darker skin tones and resolves over months.

Pityriasis Lichenoides

Classification

Pityriasis lichenoides exists on a spectrum ranging from the acute form, pityriasis lichenoides et varioliformis acuta (PLEVA), to the chronic form, pityriasis lichenoides chronica (PLC). It is more common in children and young adults with a male predominance. The pathogenesis is incompletely understood and may represent a T-cell lymphoproliferative disorder or an inflammatory response to infection (EBV, HIV, toxoplasma).

PLEVA (Mucha-Habermann Disease)

PLEVA presents with an acute onset of polymorphic papules at various stages of evolution: erythematous papules, vesicles, necrotic crusts, and varioliform (pox-like) scars. Lesions favor the trunk and proximal extremities and appear in crops. Mild systemic symptoms such as fever and malaise may accompany the eruption. Febrile ulceronecrotic Mucha-Habermann disease (FUMHD) is a rare, severe variant with high fever, extensive skin necrosis, and potential mortality that requires aggressive management.

PLC

PLC is more indolent, presenting with small, red-brown papules with characteristic mica-like adherent scale. Lesions come in crops over months to years, and individual lesions resolve with hypopigmentation. PLC is less symptomatic than PLEVA.

Histopathology

Histopathology shows interface dermatitis with a wedge-shaped lymphocytic infiltrate, extravasated erythrocytes, and parakeratosis. PLEVA shows more pronounced necrosis and vasculitis. It is important to rule out lymphomatoid papulosis (LyP), in which CD30+ atypical lymphocytes are present.

Management

Observation is appropriate for mild cases, as most resolve spontaneously over months to years. Phototherapy (NB-UVB) is effective for widespread disease. Erythromycin or azithromycin, used for their anti-inflammatory properties, are appropriate for children. Methotrexate is reserved for recalcitrant PLEVA or FUMHD, and dapsone serves as an alternative systemic agent. Regular follow-up is warranted to monitor for the rare transformation to mycosis fungoides or lymphomatoid papulosis.

<image>Clinical comparison of pityriasis lichenoides et varioliformis acuta (PLEVA) showing polymorphic necrotic papules in various stages on the trunk, versus pityriasis lichenoides chronica (PLC) with red-brown papules and mica-like scale</image>

Lichen Striatus

Lichen striatus is a self-limited, linear dermatosis following the lines of Blaschko, primarily affecting children ages 2 to 15 with a female predominance. It presents as a unilateral, linear band of flat-topped, skin-colored to erythematous papules extending along an extremity. Nail involvement may occur, presenting as longitudinal ridging, splitting, or onycholysis. Histopathology shows a band-like lichenoid and perivascular lymphocytic infiltrate with spongiosis. Management requires only reassurance, as the condition resolves spontaneously within 6 to 24 months. TCS may be used for symptomatic cases. Post-inflammatory hypopigmentation is common and may persist longer than the eruption itself.

Key Clinical Pearls

Diaper psoriasis in infants is commonly the first sign of psoriasis, and these patients should be monitored for future plaque development. Always obtain RPR/VDRL in sexually active adolescents with a pityriasis rosea-like eruption to exclude secondary syphilis. PLEVA can be confused with varicella because both present with lesions in multiple stages of evolution simultaneously. Lichen striatus following Blaschko lines reflects genetic mosaicism and should not be confused with a dermatome distribution. Guttate psoriasis following streptococcal pharyngitis may self-resolve, but persistent cases should be managed as chronic psoriasis.

References

1. Bronckers IMGJ, Paller AS, van Geel MJ, et al. Psoriasis in children and adolescents: diagnosis, management, and comorbidities. Paediatr Drugs. 2015;17(5):373-384.
2. Drago F, Broccolo F, Rebora A. Pityriasis rosea: an update with a critical appraisal of its possible herpesviral etiology. J Am Acad Dermatol. 2009;61(2):303-318.
3. Bowers S, Warshaw EM. Pityriasis lichenoides and its subtypes. J Am Acad Dermatol. 2006;55(4):557-572.
4. Patrizi A, Neri I, Fiorentini C, Bonci A, Ricci G. Lichen striatus: clinical and laboratory features of 115 children. Pediatr Dermatol. 2004;21(3):197-204.

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