Neonatal pustular and vesiculobullous eruptions — formative SAQs

SAQ 1 (10 marks)

A ten-day-old term neonate presents with a one-day history of fever, lethargy and poor feeding, and is found to have clustered vesicles on an erythematous base on the scalp at the site of a fetal scalp electrode. The baby was born vaginally to a mother who reported a first episode of genital herpes in the week before delivery. [6]

Question: Outline the diagnosis, the immediate investigations, and the management of this neonate, including the aciclovir regimen and the principle that governs the decision to start it. (10 marks) [6] [7]

Model answer

Diagnosis and recognition (2 marks). The most likely diagnosis is neonatal herpes simplex. The clustered vesicles on an erythematous base at the scalp-electrode site, the fever and lethargy, and the maternal primary first-episode genital herpes near delivery (the highest-risk scenario for transmission) together make this herpes simplex until proven otherwise. This is a neonatal emergency. [6]

Immediate investigations (3 marks). Perform a full sepsis evaluation — full blood count and differential, C-reactive protein, blood culture, urinalysis and urine culture, and liver function tests looking for the hepatitis of disseminated disease. The herpes-specific workup is HSV PCR taken from surface swabs (conjunctiva, mouth, nasopharynx, rectum) and from any skin vesicle, blood PCR, and cerebrospinal fluid for cell count, protein, glucose and HSV PCR. PCR has replaced viral culture as the diagnostic standard because it is faster and more sensitive. [7] [6]

Management and the aciclovir regimen (3 marks). Start intravenous aciclovir at 20 mg/kg every eight hours promptly after taking samples, without waiting for the PCR results, because delayed aciclovir increases mortality and long-term neurodevelopmental morbidity. Add broad-spectrum antibiotics to cover neonatal sepsis while results are pending. The total duration is guided by disease category: 14 days for skin-eye-mouth disease and 21 days for central-nervous-system and disseminated disease, with follow-on specialist-led suppression and surveillance. Admit, monitor for disseminated disease, and involve paediatric infectious diseases. [6] [7]

The governing principle and safety-net (2 marks). The principle is that a vesicle on an ill neonate is herpes simplex until proven otherwise, and the well-or-ill call is the single most powerful discriminator in this topic — treatment cannot wait for the confirmatory test. On recovery, arrange the follow-up surveillance for recurrence and neurodevelopment, and coordinate with paediatric infectious diseases for the long-term plan. [6]

SAQ 2 (10 marks)

A two-day-old term neonate on the postnatal ward is noted to have scattered pale-yellow pustules on an erythematous base across the trunk and proximal limbs. The baby is feeding well, is afebrile, pink and warm, and behaves normally. The palms and soles are spared. [2]

Question: Discuss the differential diagnosis, the bedside assessment including the smear, and your management of this neonate, contrasting it with the dangerous blistering presentations you must not miss. (10 marks) [1] [2]

Model answer

Likely diagnosis and differential (2 marks). The most likely diagnosis is erythema toxicum neonatorum — the follicular, erythema-based pustule peaking at 24 to 48 hours in a completely well neonate, sparing the palms and soles, and the commonest benign neonatal pustular eruption. The differential includes transient neonatal pustular melanosis (present at birth, no erythematous base, involves palms and soles, leaves hyperpigmentation) and neonatal cephalic pustulosis (facial, first weeks), the other benign eruptions. [2] [3]

Bedside assessment and the smear (2 marks). Confirm the wellness of the baby using a neonatal assessment approach — feeding, temperature stability, tone, perfusion and behaviour — and characterise the lesion (follicular pustule on an erythematous base, sparing palms and soles). Where doubt remains, a Wright or Giemsa-stained smear of the pustule contents settles it: erythema toxicum shows eosinophils and transient neonatal pustular melanosis shows neutrophils, and both are culture-negative, distinguishing them from a bacterial pustule or herpetic vesicle. [2] [3]

Management of this neonate (2 marks). Confirm the benign diagnosis clinically (and with the smear if in doubt), give no active treatment, explain the natural history and self-resolution, and provide a clear safety-net for return — fever, poor feeding, lethargy, or any change in the lesions. Reassuring the well baby with a secure diagnosis is correct stewardship; the only error is reassuring an insecure diagnosis. [1] [2]

The dangerous presentations not to miss (3 marks). Contrast this with the dangerous blistering neonate: an ill or febrile neonate with clustered or disseminated vesicles (neonatal herpes simplex — full sepsis workup, HSV PCR and empiric intravenous aciclovir); widespread tender erythema with flaccid bullae, sheet-like desquamation and a positive Nikolsky sign with spared mucosae (staphylococcal scalded skin syndrome — admit for intravenous anti-staphylococcal therapy and burn-style care); blistering from birth at friction sites (epidermolysis bullosa — minimise handling, non-adherent dressings, biopsy and specialist referral); and a linear blaschkoid vesicular eruption in a female (incontinentia pigmenti — dermatology, IKBKG testing and extracutaneous screens). [6] [10]

Governing principle (1 mark). The single most powerful discriminator is the well-or-ill call: the well baby with a clearly benign morphology is reassured with a safety-net, while the ill or atypical baby is escalated to a full sepsis workup and empiric aciclovir. A benign-looking lesion on a sick baby is still a sick baby. [1] [6]