20.1 Common Pediatric Dermatology

Common Pediatric Dermatology

Why This Matters for the Exam

Skin findings are among the most frequent presenting complaints in general pediatric outpatient practice, and the ABHS Part 1 written paper regularly tests recognition of classic morphology, the ability to distinguish look-alike conditions, and knowledge of red-flag findings that change management. Expect several single-best-answer items built around a brief vignette plus a described lesion rather than a photograph.

Atopic Dermatitis (Brief Overview — See Allergy/Immunology Chapter)

Atopic dermatitis (AD), also called eczema, is a chronic, relapsing, intensely pruritic inflammatory skin condition driven by skin-barrier dysfunction and Type 2 (allergic) inflammation. The full pathophysiology, the atopic march, and the step-up treatment ladder (emollients, topical corticosteroids, topical calcineurin inhibitors, and biologic agents such as dupilumab) are covered in the Allergy and Immunology chapter. For this chapter, the exam-relevant points to retain are:

• Distribution changes with age. Infants (under 2 years) tend to have AD on the face, scalp, and extensor surfaces of the limbs, while diapered skin is typically spared. Older children and adolescents develop the classic flexural pattern — antecubital and popliteal fossae, neck, wrists, and ankles.
• Cardinal features: a chronic/relapsing course, intense pruritus, and dry skin (xerosis), usually with a personal or family history of atopy (asthma, allergic rhinitis, or AD itself).
• Secondary bacterial infection (usually with Staphylococcus aureus) is common because scratching breaks the skin barrier — look for weeping, crusting, or honey-colored crust superimposed on chronic eczematous plaques.

Diaper Dermatitis: Irritant vs Candidal

Diaper-area rashes are extremely common, and distinguishing simple irritant contact diaper dermatitis from candidal diaper dermatitis is a favorite exam distinction because the management differs.

Exam trap: a diaper rash that fails to improve after 2–3 days of barrier ointment and frequent changes should raise suspicion for candidal superinfection — the correct next step is to add a topical antifungal, not simply to intensify irritant-dermatitis measures.

Common Infectious Skin Conditions

Impetigo

Impetigo is the most common bacterial skin infection of childhood, caused by Staphylococcus aureus and/or Group A Streptococcus (GAS).

• Non-bullous impetigo (about 70% of cases): begins as a papule or vesicle that ruptures to leave a characteristic honey-colored crust; caused by S. aureus alone or a mix of S. aureus and GAS.
• Bullous impetigo: flaccid, easily ruptured bullae caused by exfoliative-toxin-producing S. aureus; more common in neonates and infants.
• Treatment: topical mupirocin for limited, localized disease; oral antibiotics (e.g., a first-generation cephalosporin) for extensive or bullous disease.
• Highly contagious through self-inoculation and close contact; children should be excluded from school or daycare until at least 24 hours of appropriate treatment.

Molluscum Contagiosum

Caused by a poxvirus, molluscum contagiosum presents as multiple small, flesh-colored, dome-shaped papules with a characteristic central umbilication. It spreads by direct skin contact, autoinoculation (scratching spreads lesions in a line), and fomites, and is common in school-age children. It is a self-limited condition, typically clearing within 6–18 months without any treatment; observation is appropriate for most children. Curettage, cryotherapy, or topical cantharidin can be offered for extensive, cosmetically troubling, or persistent lesions, or in immunocompromised children where lesions can be atypically large and numerous.

Tinea (Dermatophyte) Infections

• Tinea corporis (ringworm of the body): an annular, scaly plaque with a raised, advancing border and central clearing. Treated with a topical antifungal (e.g., terbinafine or clotrimazole).
• Tinea capitis: scalp scaling with patchy hair loss, sometimes with a black-dot pattern from hairs broken at the scalp surface, or a boggy, inflamed kerion if a strong host inflammatory response occurs. Unlike tinea corporis, tinea capitis requires an oral antifungal (griseofulvin or terbinafine) because topical agents cannot penetrate the hair follicle. A Wood's lamp fluoresces green only with Microsporum species; most tinea capitis worldwide is caused by non-fluorescing Trichophyton species, so a negative Wood's lamp does not exclude the diagnosis.

Exam trap: selecting a topical antifungal as monotherapy for suspected tinea capitis is a classic wrong-answer choice — oral therapy is mandatory.

Infantile Hemangioma

Infantile hemangioma (IH) is the most common benign vascular tumor of infancy, arising from proliferating endothelial cells.

Natural course:

• Often absent or only a faint pale or telangiectatic herald mark at birth, followed by a rapid proliferative phase in the first weeks of life (most rapid growth in the first 5–8 weeks), with most proliferation complete by around 5 months and maximum size typically reached by 9–12 months.
• Followed by a slow, spontaneous involuting phase over subsequent years, with substantial regression by age 4 and continued improvement up to age 10.
• Most infantile hemangiomas are small, uncomplicated, and require only observation and parental reassurance.

When to treat — red-flag indications:

• Vision-threatening lesions (periocular location, risk of deprivation amblyopia or astigmatism)
• Airway-threatening lesions (beard-distribution or subglottic hemangiomas presenting with stridor)
• Ulceration — the most common complication, causing pain, bleeding, and infection risk
• Large, segmental facial hemangiomas — screen for PHACE syndrome (Posterior fossa malformation, Hemangioma, Arterial anomalies, Cardiac defects/coarctation, Eye abnormalities)
• Lumbosacral segmental hemangiomas — screen for underlying spinal dysraphism (tethered cord) with spinal imaging
• Five or more cutaneous hemangiomas — screen for hepatic hemangiomas with abdominal ultrasound

Treatment: oral propranolol is first-line, started during the proliferative phase (typically 1 mg/kg/day titrated up to 2–3 mg/kg/day) and continued for 6–12 months to maximize effect.

Exam contrast: a vascular malformation (e.g., a port-wine stain/capillary malformation) is present at birth, grows proportionally with the child, and does not involute — unlike a true infantile hemangioma.