Unilateral rash on a baby girl

Diagnosis: Asymmetric periflexural exanthem of childhood

Asymmetric periflexural exanthem of childhood (APEC) is a diagnosis defined by its unique clinical presentation. Since its original description in 1962 by Brunner ¹ as a new papular erythema of childhood, a number of names have been used to describe the same clinical process: unilateral laterothoracic exanthema,² asymmetric periflexural exanthem of childhood,³ and lichen miliaris.⁴

Clinical picture of APEC

The initial clinical finding is a unilateral erythematous macular and papular eruption, often beginning in or around the axilla. Over the following 1 to 3 weeks, centrifugal spread involves the upper and lower extremities. Approximately 70% of APEC cases have involvement of the contralateral trunk. Despite the progression to the contralateral side, the eruption remains asymmetric throughout its course.

Additional findings include lymphadenopathy and pruritus in 70% and 65% of cases, respectively. ^3-5 In contrast to other exanthems, APEC rarely involves the face.⁵ A study by Coustou reported that 60% of cases had a preceding prodrome including rhinitis, pharyngitis, otitis, and fever.^4,5

Cause is unknown

Although the precise cause of APEC is not known, it has features consistent with a viral exanthem. A viral source is supported by a springtime and pediatric predominance with spontaneous resolution. In addition, 1 adult case of APEC has been attributed to an acute Parvo B19 infection.⁶

However, consistent serologic evidence supporting a viral cause is lacking,^{2, 7} and no human transmissions have been documented except for reports of 2 familial cases.⁸ Some have proposed that this could be a childhood form of pityriasis rosea possibly caused by human herpes virus 7.⁴