Neonatal pustular and vesiculobullous eruptions — branching viva

Opening question

Examiner: Review this neonate for me. What is the most likely diagnosis, and how are you framing the problem? [1]

Candidate: The most likely diagnosis is erythema toxicum neonatorum — a follicular pustule on an erythematous base, peaking at 24 to 48 hours of life, in a completely well, afebrile, feeding neonate, sparing the palms and soles. It is the commonest of the benign neonatal pustular eruptions. My frame is two-pathway: first, confirm the baby is well and the morphology fits a benign pattern, and reassure with a safety-net; and second, keep a constant lookout for the dangerous patterns — the ill baby, the atypical vesicle, the friction blister from birth — that demand escalation. The well-or-ill call is the most powerful discriminator. [2] [1]

Examiner: How would you distinguish erythema toxicum from the other benign pustular eruptions? [2]

Candidate: Two features do most of the work — timing and the palms and soles. Erythema toxicum peaks at 24 to 48 hours and spares the palms and soles. Transient neonatal pustular melanosis is present at birth, has no erythematous base, involves the palms and soles, and evolves through a collarette of scale to hyperpigmentation; it is more common in Black newborns. Neonatal cephalic pustulosis sits on the cheeks and chin of a well baby in the first weeks. If I am still in doubt, a Wright-stained smear of the pustule settles it: erythema toxicum shows eosinophils, transient neonatal pustular melanosis shows neutrophils, and both are culture-negative. [2] [3]