Background: Four years ago, we began seeing young children with an unu
sual, predominantly unilateral, morbilliform and eczematous, self-limi
ted cutaneous eruption. It appeared to correspond to unilateral latero
thoracic exanthem (ULE) reported from France and to an eruption descri
bed as ''a new papular erythema of childhood'' in the United States. O
bjective: We conducted a prospective study of ULE to define its clinic
al evolution, pathology, and therapy. In addition, we performed epidem
iologic and microbiologic investigations in an attempt to determine th
e cause of ULE. Method: We studied 48 children with ULE. In some patie
nts, blood, urine, stool, as well as skin biopsy specimens were analyz
ed. Results: ULE is a morbilliform, eczematous eruption that often beg
ins close to the axilla and spreads to become bilateral, although it u
sually retains a unilateral predominance. Patients' mean age at onset
is 24.3 months, with a female predominance (2:1) and mean duration of
5 weeks, followed by spontaneous resolution that may or may not be imp
roved with topical corticosteroids. It is characterized by a unique ec
crine lymphocytic infiltration. Although signs of infection were repor
ted by most patients, no one infectious agent was identified. No signi
ficant epidemiologic factor was found. Conclusion: ULE, in young child
ren, is a self-limited morbilliform and scarlatiniform eruption that m
ay represent a specific skin reaction to one or more infectious agents
.