A 48-hour-old term female newborn is evaluated in the nursery for a new skin eruption. The… — USMLE Step 2 CK

A $48$ -hour-old term female newborn is evaluated in the nursery for a new skin eruption. The infant was born at $39$ weeks gestation via uncomplicated vaginal delivery to a $25$ -year-old primigravid mother. The mother's prenatal screening laboratory tests were unremarkable, although she reports having had a mild, self-resolving upper respiratory tract illness $2$ weeks prior to delivery. The infant is exclusively breastfeeding every $2$ to $3$ hours and is producing normal wet and soiled diapers. Vital signs include a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), heart rate of $135\text{/min}$ , and respiratory rate of $42\text{/min}$ . On physical examination, the newborn appears comfortable and alert. Skin examination reveals a widely distributed rash consisting of $2$ - to $3$ -mm blanching, erythematous macules, many of which contain central, firm, $1$ -mm yellow-white pustules. The lesions are prominent on the trunk and face, but the palms and soles are completely spared. There is no associated lymphadenopathy, hepatosplenomegaly, or neurologic deficit. A complete blood count demonstrates a leukocyte count of $16,500/\text{mm}^3$ with an eosinophil fraction of $8\%$ . Which of the following is the most appropriate next step in the management of this patient?

A
Initiation of intravenous ampicillin and gentamicin
B
Initiation of intravenous acyclovir
C
Microscopic evaluation of a skin scraping with potassium hydroxide
Reassurance and routine newborn careAnswer
E
Application of topical mupirocin to the lesions

Answer

Reassurance and routine newborn care

The correct answer is reassurance and routine newborn care. This patient's presentation—a vigorous, afebrile

48

-hour-old neonate with a rash consisting of erythematous macules and central pustules that spares the palms and soles—is the classic description of erythema toxicum neonatorum (ETN). ETN is a benign, self-limited eruption that occurs in up to

50\%

of full-term infants, typically appearing within the first

24

72

hours of life. The pustules are notably sterile and filled with eosinophils, which corresponds to the mild peripheral eosinophilia seen in this patient's laboratory results. The elevated leukocyte count (

16,500/\text{mm}^3

) is within the normal physiological range for a newborn and does not indicate an underlying infection. Because ETN resolves spontaneously without sequelae, parental reassurance and observation are the only indicated interventions.

Step-by-Step Solution

Analyze the clinical stability and vital signs of the neonate.

The infant is vigorous, feeding well, and has normal age-adjusted vital signs with no evidence of systemic illness.

To rule out true neonatal infectious emergencies such as sepsis, which would dictate an immediate aggressive workup and empiric antibiotics.

Characterize the primary skin lesions and their distribution.

The rash consists of erythematous macules with central yellow-white pustules on the trunk and face, sparing the palms and soles, appearing on the second day of life.

To differentiate between benign neonatal rashes (e.g., erythema toxicum neonatorum) and infectious exanthems (e.g., herpes simplex virus, candidiasis, staphylococcal pustulosis).

Evaluate the laboratory findings in the context of neonatal physiology.

The leukocyte count of

16,500/\text{mm}^3

is entirely normal for a

48

-hour-old neonate (normal range

9,000

30,000/\text{mm}^3

). The

8\%

eosinophilia is an expected physiological finding strongly correlated with erythema toxicum neonatorum.

To prevent misinterpreting normal neonatal leukocytosis and condition-specific eosinophilia as a bacterial or parasitic infection.

Determine the appropriate management plan based on the synthesized clinical picture.

The diagnosis is erythema toxicum neonatorum, requiring only reassurance and routine care.

To avoid unnecessary, potentially harmful pharmacological interventions.

Key Concept

Erythema toxicum neonatorum is a benign, self-limited rash presenting in the first few days of life with erythematous macules and central pustules packed with eosinophils. It requires only clinical recognition and reassurance, avoiding unnecessary infectious disease workups and treatments.

Estimated Time:1m 15s

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