Unilateral laterothoracic exanthem (ULE), also called unilateral periflexural exanthem of childhood, is a peculiar unilateral eruption that typically occurs on the trunk in young children.

It is most often seen in the winter or spring.

The exact etiology of ULE is unknown, but it is thought to be a distinct reaction pattern to a variety of potential infectious triggers, most likely viral.

A prodrome of low-grade fevers with respiratory or gastrointestinal symptoms may occur.

The eruption begins on one side of the trunk, usually near the axilla, but occasionally on the inguinal creases. Initially lesions are pink morbilliform or eczematous macules and papules that sometimes have a surrounding pale halo. The lesions may coalesce (Fig. 7.12).

The eruption spreads centrifugally and may become bilateral but always maintains predominance on the originating side.

Over time, lesions become scaly and may develop a central dusky or gray color.

Pruritus may occur and is usually mild.

Resolves with desquamation.

Diagnosis is based on clinical recognition.