Neonate with Vesicles on the Scalp: Herpes Simplex Versus Erythema Toxicum
A 9-day-old term girl is brought to the clinic by her mother for a rash that appeared 24 hours ago. She has been feeding well, is afebrile (36.9 °C rectal), and the mother reports no lethargy or irritability. On exam, there are 6 to 8 grouped 2-3 mm vesicles with an erythematous base clustered on the left parietal scalp, plus a few scattered 1-2 mm pustules on the trunk. The scalp lesions do not cross the midline. The mother had no known history of genital herpes, but she reports a 'cold sore' 2 weeks before delivery. The infant is otherwise thriving. A Wright-stained smear of a pustule on the trunk shows eosinophils only. The scalp vesicle fluid is being sent for HSV PCR. The family lives 45 minutes from the nearest pediatric emergency department.
1. Does the presence of eosinophils on the trunk pustule smear and an afebrile, feeding infant allow you to conclude the scalp lesions are benign and send the infant home? Justify your reasoning.
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No. Eosinophils on a Wright stain of a trunk pustule are characteristic of erythema toxicum neonatorum (ETN), which is benign and self-limited. However, ETN does not produce grouped vesicles on an erythematous base, and it does not typically localize as a unilateral scalp cluster. The presence of ETN-like pustules elsewhere does not exclude a second, more serious process.
Key reasoning:
- Grouped vesicles in a neonate must be treated as HSV until proven otherwise, regardless of afebrile status. Neonatal HSV can present with skin, eye, and mouth (SEM) disease without systemic signs early on, but can progress to CNS or disseminated disease.
- Maternal history of a cold sore 2 weeks before delivery (even without known genital HSV) is a relevant risk factor; primary or recurrent HSV can be asymptomatic and can be transmitted perinatally or postnatally.
- Age < 28 days is the critical threshold: any neonate with vesicular lesions warrants a full sepsis/HSV evaluation (surface swabs, blood PCR, CSF PCR, ALT, and empiric IV acyclovir) until PCR results return.
- The 45-minute distance from an ED is a safety constraint: if the infant deteriorates, delay in access to care is dangerous.
Conclusion: The correct action is not reassurance and discharge. The infant needs urgent evaluation with HSV PCR of the vesicle, surface cultures/swabs, and consideration of empiric IV acyclovir pending results, with close follow-up.
2. If the scalp vesicle HSV PCR returns positive at 24 hours, what is the immediate management, and what determines the duration of therapy?
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A positive HSV PCR from a neonatal vesicle confirms neonatal HSV disease and mandates admission and intravenous acyclovir (typically 20 mg/kg/dose every 8 hours in neonates, per local protocol).
Immediate steps:
- Full diagnostic evaluation if not already done: HSV PCR of blood and CSF, surface swabs (conjunctiva, mouth, rectum), liver enzymes (ALT), and CBC. Ophthalmologic exam and, if CNS involvement suspected, neuroimaging.
- Initiate IV acyclovir without waiting for CSF results; do not delay for LP if the infant is unstable.
- Supportive care and monitoring for disseminated disease (hepatitis, coagulopathy, pneumonitis).
Duration depends on disease category:
- SEM (skin, eye, mouth) disease: IV acyclovir for 14 days.
- CNS disease or disseminated disease: IV acyclovir for 21 days, with repeat CSF PCR near end of therapy to confirm clearance in CNS disease.
Prognosis is best with early treatment; SEM disease has the best outcomes, while CNS and disseminated disease carry higher morbidity and mortality. Close neurodevelopmental follow-up is warranted.