Laboratory Studies
Because of the distinctive appearance of the lesions, the nontoxic status of the neonate, and the evanescent nature of the eruption, the diagnosis is usually clear. If any doubt about the diagnosis exists, further studies may be needed to evaluate for an underlying bacterial, viral, or fungal disease.
A simple Gram stain or Wright stain should reveal evidence of a sterile pustule populated primarily by eosinophils. The presence of neutrophils suggests an infectious cause. Peripheral blood studies may also reveal a circulating eosinophilia.
Results from a direct slide (fluorescent antibody testing) of a smear or a Tzanck preparation should be negative for herpes simplex (or, rarely, varicella-zoster virus) because these are reasonably sensitive tests for these particular viruses.
A simple potassium hydroxide preparation can be performed to evaluate for fungal infection, such as congenital cutaneous candidiasis.
Blood cultures and appropriate workup for neonatal sepsis from group B Streptococcus, Listeria, Escherichia coli, and other pathogens should be considered in the appropriate context of illness in a neonate.
A skin biopsy may be necessary if the diagnosis is unclear.
Histologic Findings
Hyperkeratosis, follicular plugging, and accumulation of primarily eosinophils with some neutrophils in the follicular epithelium.
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A 5-day-old newborn with erythematous papules with surrounding indistinct blotchy erythema visible on the abdomen. Image courtesy of Jining I. Wang, MD.
