Diagnosis: Molluscum Contagiosum
The most likely diagnosis is molluscum contagiosum, based on the pathognomonic presentation of flesh-colored, dome-shaped, pearly papules with central umbilication (depressions) on the upper extremities in an otherwise healthy 2-year-old child. 1
Clinical Reasoning
The clinical presentation is classic for molluscum contagiosum:
- Characteristic morphology: Flesh-colored, dome-shaped, pearly lesions with central depressions (umbilication) are the hallmark features of molluscum contagiosum 1, 2
- Location: Upper extremities are a common site for molluscum contagiosum, which is transmitted by direct skin contact and autoinoculation 1
- Absence of pruritus: Unlike the patient's known atopic dermatitis (which is pruritic by definition), these new lesions are not itchy, making them distinct from an atopic dermatitis flare 3
- Different from baseline atopic dermatitis: The parents correctly note these lesions differ from his usual eczema, which affects flexural areas (inside of elbows) and is itchy 3
Why Other Diagnoses Are Less Likely
- Atopic dermatitis requires pruritus as a mandatory diagnostic criterion, and typically presents with erythema, xerosis, and excoriations in age-specific distributions (cheeks/forehead in infants, flexural areas in older children) 3
- Contact dermatitis would present with erythema, vesicles, and pruritus in areas of exposure to irritants, not discrete dome-shaped papules with central umbilication 4
- Scabies presents with intense pruritus (especially at night), burrows, and predilection for web spaces, wrists, and axillae—not dome-shaped umbilicated papules 2
- Insect bites typically show erythematous papules or wheals with central punctum, often pruritic, and lack the pearly dome-shaped appearance with umbilication 2
Important Clinical Context
- Self-limited course: Molluscum contagiosum is typically self-limited in immunocompetent children, resolving spontaneously in 6-9 months, though duration is variable 1
- Atopic dermatitis association: Children with atopic dermatitis (like this patient) have higher numbers of molluscum lesions and increased likelihood of developing molluscum dermatitis (eczematous reaction around lesions) 5
- No acute intervention required: In an otherwise healthy, immunocompetent child with localized disease and no complications, active treatment is not mandatory 1
Red Flags to Monitor
- Extensive or atypical lesions: Giant, ulcerating, or rapidly spreading molluscum can indicate immunodeficiency and warrants HIV testing, especially in high-risk populations 6, 7
- Molluscum dermatitis: Watch for eczematous changes around lesions, which occur in 38.8% of patients and are more common in those with atopic dermatitis 5
- Secondary bacterial infection: Look for crusting, weeping, or honey-colored discharge requiring antibiotic coverage 8, 9