What is the diagnosis and appropriate treatment for crusted erythematous lesions in an 18‑month‑old child?

Diagnosis and Management of Crusted Erythematous Lesions in an 18-Month-Old

The most likely diagnosis is impetigo, and treatment should consist of either topical mupirocin applied three times daily for 8-12 days or oral antibiotics (cephalexin or dicloxacillin) for 7-10 days if lesions are numerous or widespread. 1, 2

Diagnostic Approach

The clinical presentation of crusted erythematous lesions in an 18-month-old child most commonly represents impetigo, which typically manifests as erythematous papules that evolve into vesicles and pustules, then rupture to form characteristic honey-colored crusts on an erythematous base 1. This age group falls within the peak incidence period, as 60-80% of certain pediatric skin conditions develop during the first year of life, with continued susceptibility through early childhood 1.

Key Distinguishing Features to Assess:

• Impetigo characteristics: Honey-colored crusts, lesions on exposed areas (face and extremities), absence of systemic symptoms, possible regional lymphadenitis 1
• Bullous vs. nonbullous pattern: Bullous impetigo shows flaccid bullae that rupture leaving thin brown crusts; nonbullous shows thick crusts from ruptured pustules 1
• Distribution pattern: Impetigo remains well-localized but frequently multiple; if perioral distribution with ongoing topical steroid use, consider perioral dermatitis 3, 4
• Associated symptoms: Presence of pruritus suggests atopic dermatitis; absence of itch is atypical for eczema but does not exclude it 1, 5

Critical Differential Diagnoses to Exclude:

Atopic dermatitis presents with symmetrical distribution, chronic relapsing course (>2 months in infancy), and typically involves cheeks, neck, trunk, and extensor surfaces in this age group, with notable sparing of the diaper area 1, 6. However, acute AD lesions show erythema with serous exudates rather than honey-colored crusts 6.

Bacterial superinfection of atopic dermatitis is suggested by crusting, weeping, purulent exudate, or pustules, requiring systemic antibiotics 3. This represents Staphylococcus aureus superimposed on underlying eczema.

Staphylococcal scalded skin syndrome (SSSS) presents with extremely tender flaccid bullae that are Nikolsky sign-positive, affecting flexures with a scalded appearance after rupture 7. This is a medical emergency requiring immediate hospitalization.

Treatment Algorithm

First-Line Management for Impetigo:

For localized lesions (few in number):

• Topical mupirocin ointment applied three times daily for 8-12 days achieves 71-93% clinical efficacy with 94-100% pathogen eradication 1, 2
• Alternative: topical retapamulin if mupirocin resistance suspected 1

For numerous or widespread lesions:

• Oral cephalexin or dicloxacillin for 7-10 days (most S. aureus isolates from impetigo are methicillin-susceptible) 1, 3
• If MRSA suspected or confirmed: clindamycin, trimethoprim-sulfamethoxazole, or doxycycline (though doxycycline avoided in children <8 years due to tooth staining) 1
• Systemic therapy is preferred for multiple lesions or outbreaks to decrease transmission 1

Obtain Cultures Before Treatment:

Culture vesicle fluid, pus, or erosions to establish the causative organism, particularly if treatment failure occurs or MRSA is suspected 1. However, do not delay antibiotic initiation while awaiting culture results if clinical infection is evident 3.

Adjunctive Skin Care:

• Gently cleanse affected areas with mild, pH-neutral non-soap cleansers 3
• Apply fragrance-free emollients to surrounding dry skin after gentle washing 3
• Avoid occlusive dressings over active lesions 1

Management if Atopic Dermatitis is Suspected

If the presentation suggests atopic dermatitis with secondary bacterial infection rather than primary impetigo:

1. Treat bacterial superinfection first with oral flucloxacillin or cephalexin for 7-10 days 3
2. Liberal application of fragrance-free emollients immediately after 10-15 minute lukewarm baths, regardless of severity 1, 5
3. Topical corticosteroids appropriate for age and site once infection is controlled 1
4. Avoid all topical steroids on facial skin if perioral dermatitis is suspected, as this represents an iatrogenic condition from inappropriate facial steroid application 3, 4

Critical Pitfalls to Avoid

• Never use topical antibiotics alone for extensive impetigo: Systemic therapy is required for numerous lesions to prevent complications and reduce transmission 1
• Do not assume all crusted lesions are impetigo: Grouped punched-out erosions or vesiculation indicate viral superinfection (eczema herpeticum) requiring acyclovir 3, 6
• Avoid restarting topical steroids on facial skin if perioral dermatitis is present, as this causes steroid-induced atrophy and worsens the condition 3
• Do not delay treatment for SSSS: If extremely tender flaccid bullae with positive Nikolsky sign are present, this is a medical emergency with 4% mortality in children requiring immediate hospitalization and IV antibiotics 7
• Obtain bacteriological swabs from crusted areas before antibiotics, but do not delay treatment if clinical infection is evident 3

Follow-Up and Monitoring

• Reassess within 48-72 hours to evaluate response to antibiotics 3
• If no improvement after completing appropriate antibiotic course, consider MRSA, treatment non-adherence, or alternative diagnosis 1
• Refer to dermatology if diagnostic uncertainty exists or no improvement after 4 weeks of appropriate treatment 3