During routine morning rounds in the newborn nursery, a physician evaluates a male neonate… — USMLE Step 2 CK

During routine morning rounds in the newborn nursery, a physician evaluates a male neonate at $48$ hours of life due to a newly developed cutaneous eruption. The infant was born at $39$ weeks gestation via an uncomplicated spontaneous vaginal delivery to a $26$ -year-old primigravida. The mother's prenatal laboratory screening was unremarkable. The infant has been breastfeeding robustly and passing normal transitional stools. Vital signs demonstrate a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), a heart rate of $138/\text{min}$ , and a respiratory rate of $38/\text{min}$ . Physical examination highlights a well-appearing, alert neonate. A widely disseminated rash consisting of prominent erythematous macules and papules is visible across the anterior thorax, back, and proximal thighs. Several of the erythematous bases contain small, $1\text{- to }2\text{-mm}$ central yellowish pustules. The palms and plantar surfaces are completely clear of lesions. A Wright-stained smear of the pustular contents is examined under light microscopy and demonstrates a striking predominance of eosinophils. Based on these findings, which of the following is the most appropriate next step in management?

A
Transfer to the intensive care unit and initiate intravenous acyclovir
Continue routine newborn care and reassure the familyAnswer
C
Obtain blood and cerebrospinal fluid cultures, then administer intravenous vancomycin and cefotaxime
D
Isolate the infant and administer the live-attenuated varicella-zoster vaccine
E
Prescribe a $5$ -day course of topical mupirocin ointment

Answer

Continue routine newborn care and reassure the family.

The clinical presentation of a well-appearing neonate with a widely disseminated rash consisting of erythematous macules and central pustules, sparing the palms and soles, is the classic description of erythema toxicum neonatorum (ETN). The diagnosis is confirmed by the presence of numerous eosinophils on a Wright-stained smear of the pustular contents. ETN is a completely benign, self-limited condition that typically appears in the first few days of life and resolves without any medical intervention. The infant's reassuring vital signs and normal feeding further rule out an infectious etiology. Therefore, the most appropriate management is reassurance and routine newborn care.

Step-by-Step Solution

Analyze the patient's clinical presentation and vital signs.

The patient is a well-appearing, afebrile

48

-hour-old neonate feeding normally, which significantly lowers the pre-test probability of severe systemic infections like neonatal sepsis or disseminated herpes simplex virus (HSV).

Vital signs and general appearance are critical primary branching points in neonatal care to separate benign physiologic variants from life-threatening emergencies.

Evaluate the morphological features and distribution of the rash.

The rash consists of erythematous macules with central pustules that spare the palms and soles.

Specific rash morphology helps narrow the differential diagnosis. Sparing of palms and soles strongly suggests erythema toxicum neonatorum (ETN), whereas involvement might point toward congenital syphilis or other infectious etiologies.

Interpret the laboratory findings from the pustular smear.

The Wright stain shows a predominance of eosinophils.

Microscopic analysis of pustular contents is the definitive diagnostic step. Eosinophils confirm ETN, whereas neutrophils would suggest transient neonatal pustular melanosis or staphylococcal pustulosis.

Determine the appropriate management based on the confirmed diagnosis.

Because ETN is a benign, self-limiting condition, the correct management is purely observational.

Intervening with antibiotics or antivirals would violate antimicrobial stewardship and introduce unnecessary iatrogenic risks.

Key Concept

Distinguishing benign neonatal rashes (Erythema Toxicum Neonatorum) from infectious pediatric dermatoses to avoid unnecessary pharmacological interventions.

Estimated Time:1m 0s

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