Fever and clustered vesicles in a toddler with atopic dermatitis
A 14-month-old boy with moderate-to-severe atopic dermatitis since 4 months of age, managed with emollients and intermittent topical corticosteroids, is brought in with 3 days of fever to 38.7 C, poor feeding, and a striking eruption on the face and neck. Examination shows his usual flexural eczematous patches plus, on both cheeks, the perioral area, and the anterior neck, tightly clustered 1-2 mm monomorphic umbilicated vesicles and punched-out erosions, some with hemorrhagic crusts. A single 6 mm eroded plaque without satellite lesions sits on the upper back. He is irritable but alert, with normal capillary refill and no hypotension. His 5-year-old brother has had recurrent cold sores. He has received no varicella or MMR vaccine; his record is otherwise current. He weighs 11 kg. A rapid influenza test is negative.
1. State your leading diagnosis and use specific features to argue against three alternatives.
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This is eczema herpeticum (Kaposi varicelliform eruption): monomorphic umbilicated vesicles and punched-out erosions clustered exactly within active eczematous skin, with fever and poor feeding, in a child whose sibling has active herpes labialis.
Against impetiginization: impetigo produces honey-colored crusts and irregular erosions rather than tightly clustered umbilicated vesicles, and a febrile toxic presentation is unusual unless there is extensive cellulitis. The two often coexist, so a bacterial swab is still warranted. Against varicella: chickenpox is centripetal, with lesions at multiple stages on trunk and scalp, not confined to eczematous areas, and the sibling history is cold sores, not chickenpox. Against hand-foot-mouth disease: coxsackievirus causes an oral enanthem with acral vesicles and is typically less facial; it does not produce perioral umbilicated vesicles tightly grouped on eczema. A primary inoculation site or bacterial coinfection could explain the solitary back plaque, which lacks the satellite lesions of disseminated herpes.
The monomorphism and the predilection for barrier-disrupted skin are the discriminating features; do not wait for virology to treat.
2. Which tests and consults do you arrange, and what treatment do you start now? Give drug, dose, and route.
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Admit him and start IV acyclovir immediately without waiting for results: 20 mg/kg per dose (equivalent to 1,500 mg/m2/day divided every 8 hours) is roughly 220 mg IV every 8 hours for 11 kg. Ensure hydration and check renal function before and during dosing.
Diagnostics: unroof a fresh vesicle and swab the base for HSV PCR - far more sensitive than Tzanck smear - and send VZV PCR if the picture is uncertain. Swab crusted or purulent areas for bacterial culture, since Staphylococcus aureus coinfection is common and is a major cause of deterioration. Send CBC, electrolytes, BUN/creatinine, and liver enzymes. Obtain urgent ophthalmology assessment with fluorescein staining, because herpetic keratitis can occur without eye complaints and needs antiviral and topical management.
Add empiric antistaphylococcal cover (for example clindamycin or cephalexin, chosen for local resistance patterns) if there is purulence or extensive crusting. Continue emollients; topical corticosteroids to eczematous areas may continue under antiviral cover but never as treatment for the vesicles. Use contact precautions and advise the family that the brother's cold sores should be covered and hands washed.
3. Counsel the parents on recurrence risk and the long-term plan.
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Eczema herpeticum recurs in a minority of children, with reported rates in the range of 10-25%, and the risk tracks with poorly controlled atopic dermatitis and skin barrier disruption. The most effective prevention is therefore proactive eczema control: liberal emollients, adequate topical corticosteroid potency and duration for active lesions, and proactive intermittent topical anti-inflammatory therapy to previously involved sites.
Routine antiviral prophylaxis is not indicated after a single episode; it can be considered for frequent or severe recurrences, in discussion with pediatric infectious diseases. Practical advice: avoid direct contact with active cold sores, no sharing of towels or utensils, hand hygiene, and short fingernails to limit autoinoculation. Teach the red flags - fever with new clustered vesicles or punched-out erosions - and instruct them to return the same day rather than wait, because early acyclovir prevents severe disease and keratitis.
Once he has recovered, ensure varicella and MMR vaccination; live vaccines are postponed during acute illness and high-dose systemic corticosteroid therapy, but atopic dermatitis itself is not a contraindication. Arrange follow-up within 1-2 weeks to reassess eczema control and the need for a step-up regimen.