A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 4-day-old newborn is presented to the physician because of a generalized rash for the past day. He was born at term. The mother had no prenatal care and has a history of gonorrhea, which was treated 4 years ago. The newborn is at the 50th percentile for head circumference, 60th percentile for length, and 55th percentile for weight. The vital signs include: temperature 36.8°C (98.2°F), pulse 152/min, and respirations 51/min. Examination shows an erythematous maculopapular rash and pustules with an erythematous base over the trunk and extremities, sparing the palms and soles. The remainder of the examination shows no abnormalities. Which of the following is the most likely diagnosis?
-
A
AcropustulosisIncorrect. Acropustulosis of infancy involves pruritic vesiculopustules on the hands and feet of older infants, not generalized trunk/extremity rash sparing palms and soles in a 4-day-old.
-
B
Congenital syphilisIncorrect. Congenital syphilis classically involves the palms and soles and presents with snuffles, hepatosplenomegaly, and bony findings; the rash here spares palms and soles.
-
C
Erythema toxicumCorrect. A benign self-limited rash of erythematous macules, papules, and pustules sparing palms and soles in a healthy term newborn at day 4 is classic erythema toxicum neonatorum.
-
D
Pustular melanosisIncorrect. Pustular melanosis presents at or shortly after birth with rapidly rupturing pustules leaving hyperpigmented macules with a collarette of scale, more typical in Black infants.
-
E
Neonatal herpes simplex virus infectionIncorrect. Neonatal HSV presents with grouped vesicles, often with skin/eye/mouth or CNS involvement and systemic illness, not benign self-limited pustules on a well-appearing 4-day-old.
↑ Tap an answer to reveal the reasoning
Answer: C. A term newborn at day 4 of life with a generalized erythematous maculopapular rash and small pustules with an erythematous base over the trunk and extremities, sparing the palms and soles, with otherwise normal examination, has erythema toxicum neonatorum. ETN is a benign, self-limited rash that appears in 30–70% of full-term newborns, usually between days 1 and 4 of life. It is characterized by 1–3 mm yellow-white papules and pustules on an erythematous base ('flea-bitten' appearance) that wax and wane over 1–2 weeks and resolve without treatment.
The etiology is unknown but probably reflects a transient immune response in the newborn skin. A smear of pustule contents shows eosinophils — a key diagnostic clue distinguishing ETN from infectious causes. Reassurance is the only treatment.
Key differentials:
- Pustular melanosis: more common in Black newborns, present at birth, with pustules that rupture quickly to leave hyperpigmented macules surrounded by a collarette of scale; smear shows neutrophils.
- Congenital syphilis: rash on palms and soles (this rash explicitly spares them) with hepatosplenomegaly, snuffles, and bony abnormalities.
- Acropustulosis of infancy: recurrent pruritic pustules on the hands and feet of older infants (usually 2–10 months old).
**Why each option:**
**A.** Acropustulosis of infancy involves pruritic vesiculopustules on the hands and feet of older infants, not generalized trunk/extremity rash sparing palms and soles in a 4-day-old.
**B.** Congenital syphilis classically involves the palms and soles and presents with snuffles, hepatosplenomegaly, and bony findings; the rash here spares palms and soles.
**C.** Correct. A benign self-limited rash of erythematous macules, papules, and pustules sparing palms and soles in a healthy term newborn at day 4 is classic erythema toxicum neonatorum.
**D.** Pustular melanosis presents at or shortly after birth with rapidly rupturing pustules leaving hyperpigmented macules with a collarette of scale, more typical in Black infants.