What is the likely diagnosis for a 30-month-old child with a history of eczema (atopic dermatitis) presenting with multiple itchy vesicles and pustules on the hand with an erythematous base?

Eczema Herpeticum (Herpes Simplex Superinfection)

The most likely diagnosis is eczema herpeticum, a potentially life-threatening herpes simplex virus superinfection that occurs in children with underlying atopic dermatitis and requires immediate antiviral treatment. 1, 2

Clinical Recognition

This 30-month-old child presents with the classic triad for eczema herpeticum:

• Pre-existing atopic dermatitis (eczema) - the primary risk factor 1, 2
• Multiple vesicles and pustules - characteristic morphology 1
• Erythematous base with pruritus - typical inflammatory presentation 1

Grouped, punched-out erosions or vesiculation in a child with known eczema generally indicate herpes simplex infection. 1 The hand location is consistent with eczema herpeticum, which can affect any area of compromised skin barrier. 2, 3

Why This Diagnosis Takes Priority

Eczema herpeticum carries a 10% mortality rate if untreated and can lead to systemic compromise, making it a medical emergency that must be recognized promptly. 2 The condition is frequently missed or overlooked in clinical practice, leading to potentially catastrophic outcomes. 2

Diagnostic Confirmation

• Send swabs for virological screening immediately if herpes simplex infection is suspected 1
• Electron microscopy of a smear can provide rapid confirmation 1
• Clinical diagnosis is often sufficient to initiate treatment given the urgency 2, 3

Immediate Management

Systemic antiviral therapy with acyclovir is the cornerstone of treatment:

• Intravenous acyclovir is indicated for this child given the widespread eruptions and likely systemic symptoms (fever, malaise) 3
• Oral acyclovir may be considered only for very limited disease without systemic symptoms 3
• Hospital admission is warranted for patients with widespread eruptions or any systemic symptoms such as fever, malaise, or poor oral intake 3

Critical Pitfalls to Avoid

Do not mistake eczema herpeticum for:

• Bacterial superinfection - which presents with crusting and weeping rather than discrete vesicles 1
• Worsening atopic dermatitis - which lacks the characteristic punched-out erosions and uniform vesicles 1, 2
• Allergic contact dermatitis - which can cause vesicular hand lesions but typically lacks the grouped, monomorphic appearance 1, 4

The key distinguishing feature is the presence of multiple, very similar shaped and sized eroded vesicles in grouped patterns - this uniformity is pathognomonic for viral infection rather than other eczematous conditions. 3

Why Other Diagnoses Are Less Likely

While this child could theoretically have:

• Allergic contact dermatitis superimposed on atopic dermatitis 1, 4
• Bacterial superinfection (Staphylococcus aureus) 1
• Endogenous vesicular hand eczema 4

The description of "multiple itchy vesicles and pustules" with erythematous base in a child with known eczema is classic for eczema herpeticum until proven otherwise. 1, 2 The vesicular morphology specifically points away from bacterial infection (which causes crusting/weeping) and toward viral etiology. 1

Clinical Urgency

Maintain extremely high clinical suspicion when encountering any child with atopic dermatitis who presents with vesicular lesions, punched-out erosions, or systemic symptoms. 2 This is an acute, rapidly progressive disease that requires immediate recognition and treatment to prevent life-threatening complications. 2, 3