A 3-Year Old Girl with a Rash on Left Arm, Flank, and Thigh

A 3-year old girl presents with a 4-week history of rash on her left arm, flank, and thigh. The rash is non-pruritic and non-painful. The patient is taking no medications and is up-to-date on all immunizations. Her medical and family history are noncontributory. One week before the onset of the rash, the patient’s parents had taken her to her pediatrician because she had a runny nose and sore throat. A URI was diagnosed.

Discrete 1- to 2-mm erythematous papules unilaterally were distributed across the left axillae, arm, flank, and thigh. 

What’s Your Diagnosis?

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Answer: Asymmetric periflexural exanthem of childhood (APEC)

Etiology
Asymmetric periflexural exanthem of childhood (APEC) -- also known as unilateral laterothoracic exanthem -- is a fairly common childhood disorder that can rarely present in adults.^1,3-5 It tends to occur in children aged 1 to 5 years, with a mean age at diagnosis of 2 years.1,2 It affects girls twice as often as boys and occurs predominantly in the late winter and spring months.^1,2 Given the predilection of APEC for young children, seasonal occurrences, and reports of secondary cases among siblings, a viral origin seems probable; however a specific virus has not been isolated and the etiology remains unknown.^1,3,6

Clinical Course
Classically, the initial eruption starts from one axillary fold and spreads unilaterally and centrifugally on the trunk and the proximal part of the upper arm. After the first week the eruption tends to progress bilaterally, although the asymmetric pattern remains prominent.1, 2 Typically, the lesions consist of discrete 1- to 2-mm erythematous papules that coalesce to form morbilliform plaques with occasional reticulated or eczematiform aspects.1, 2 The eruption tends to spare the face and palms.^1,2 Viral-like prodromes are seen in the majority of cases; URI and GI type symptoms are the most common. Pruritus, regional lymphadenopathy, and low grade fevers often accompany the eruption.^1,2

APEC is self-limiting. Complete resolution occurs spontaneously between the 3rd and 6th week on average. Few recurrences have been reported.¹

Histology
The findings are nonspecific and include a mild-to-moderate lymphocytic infiltrate of the dermis with involvement of the sweat glands and, to a lesser extent, the hair follicles and blood vessels.¹

Differential Diagnosis
The differential diagnosis includes contact dermatitis, drug eruptions, Gianotti-Crosti syndrome (papular acrodermatitis of childhood), milia, pityriasis rosea, and scabies. The clinical features of APEC are distinct and diagnosis is usually made with little difficulty.

Treatment
APEC is self-limiting and specific treatment is not required. Topical corticosteroids and oral antibiotics are not effective; however oral antihistamines may relieve associated pruritus.

References:

References:

1. Coustou D, Leaute-Labreze C, Bioulac-Sage P, et al. Asymmetric periflexural exanthem of childhood: a clinical, pathologic, and epidemiologic prospective study. Arch Dermatol. 1999;135:799-803.
2. Carder KR, Weston WL. Atypical viral exanthems: new rashes and variations on old themes. Comtemp Pediatr. 2002;19:111-134.
3. Bodemer C, de prost Y. Unilateral laterothoracic exanthem in children: a new disease?
J Am Acad Dermatol. 1992;27(5 Pt1):693-696
4. Taieb A, Megraud F, Legrain V, et al. Asymmetric periflexual exanthem of childhood. J Am Acad Dermatol. 1993;29:391-393.
5. Chan PK, To KF, Zawar V, et al. Asymmetric periflexural exanthem in an adult. Clin Exp Dermatol. 2004;29:320-321.
6. Harangi F, Varszegi D, Szucs G. Asymmetric periflexural exanthem of childhood and viral examinations. Pediatr Dermatol. 1995;12:112-115.