Photoclinic: Asymmetric Periflexural Exanthem

This day-old, macular, blanching, nonpruritic rash had developed in the right axilla and on the right arm and right side of the trunk of a 3 1/2-year-old boy. He was otherwise asymptomatic. Other physical examination findings were unremarkable.

Sairah Chachad, MD, of Lakeland, Fla, and Deepak M. Kamat, MD, PhD, of Detroit diagnosed asymmetric periflexural exanthem--also known as unilateral laterothoracic exanthem.¹ This exanthem affects children between the ages of 1 and 4 years (mean age at onset, 2 years).² It seems to occur predominantly in females and to have seasonal variation, with peak occurrences in the spring.^1,2 Only 2 familial cases have been reported.¹

Most affected children are asymptomatic, although some complain of mild to moderate pruritus. A prodrome of GI or upper respiratory tract symptoms usually precedes the rash; further questioning showed this was the case in this patient. Regional lymph node enlargement and low-grade fever may occur at the time of the eruption.^2,3 Despite an active search for a causative agent, the etiology remains unknown.⁴

The initial eruption is classically unilateral. The rash usually appears near the axilla or thorax, but it can begin in other flexures, such as the thigh, flank, or inguinal fold.² The face, palms, and soles are spared.² The discrete, tiny erythematous papules may become confluent patches, with a serpiginous, annular, or reticulate pattern.¹ At the end of the first week, the lesions spread centrifugally to contralateral areas. The pattern is asymmetric: the side of original involvement is usually more extensively affected. After 1 to 2 weeks, the outbreak may look more scarlatiniform, morbilliform, or eczematous.² As the lesions resolve, they leave residual dry skin.

Histologic findings are nonspecific: analysis reveals a mild to moderate mononuclear interface dermatitis with occasional necrotic and apoptotic keratinocytes.³ The dermal infiltrate is predominantly around sweat glands; there is less pronounced involvement around blood vessels and hair follicles.³ Epidermal spongiosis, as well as perivascular and periappendageal inflammation, is also present. Diagnosis is usually clinical. Establishing the diagnosis limits unnecessary testing.¹

Although several conditions may mimic asymmetric periflexural exanthem, they do not share its unique unilateral distribution:

• Pityriasis rosea is often preceded by a "herald patch," and the lesions are larger and more symmetric. Older children are typically affected, and the histopathologic findings differ.²

• Unilateral eczematous conditions, such as allergic contact dermatitis and atopic dermatitis, cause much more itching; the lesions are weepy or crusted and respond well to topical corticosteroid therapy.²

• Miliaria, which typically occurs on the face, may resemble the morbilliform lesions of asymmetric periflexural exanthem.

• Roseola is transient and generalized.

• Gianotti-Crosti syndrome: the lesions of this syndrome usually develop on the face and extremities--in an acral distribution.

The prognosis for children with asymmetric periflexural exanthem is excellent. The eruption usually resolves spontaneously in 3 to 6 weeks and does not recur.¹ This child's rash resolved within 2 weeks. No hypopigmented or hyperpigmented areas were noted.

References:

REFERENCES:

1.

Pride HB. When a rash is more than a rash: skin signs of systemic disease.

Contemp Pediatr.

Nov 2000.

2.

Carder KR, Weston WL. Atypical viral exanthems: new rashes and variations on old themes.

Contemp Pediatr.

Feb 2002.

3.

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.

4.

Coustou D, Masquelier B, Lafon MD, et al. Asymmetric periflexural exanthem of childhood: microbiologic case-control study.

Pediatr Dermatol.

2000;17:169-173.