A one-sided story

March 7, 2015

Clinical Vignette

An anxious father schedules an urgent office visit for his 5-year-old boy who has a total body red bumpy rash. It started on the left flank 3 weeks ago and is still most prominent in this area (fig. 1). The boy appears well and the rash is only minimally itchy. The father refuses to leave the office until you give him the answer. What’s the diagnosis?

Diagnosis and Clinical Presentation

Diagnosis: Unilateral Laterothoracic Exanthem Unilateral laterothoracic exanthem, also known as asymmetric periflexural exanthem of childhood, is a skin eruption which typically originates unilaterally on the trunk often near the axillary region (1). Lesions then extend centrifugally to become bilateral in nearly all patients, but maintain a predominance on the initial side. The lesions consist of discrete papules which are typically 2–4 mm in diameter, and are usually erythematous. These eruptions may have various morphologies including morbilliform, scarlatiniform or eczematous papules which may become confluent.2 Diffuse asymptomatic lymphadenopathy may develop, and pruritis, which is usually mild, occurs in about half of the patients (1).

Epidemiology and pathogenesis

An infectious etiology has been assumed, but no viral or bacterial agent has ever been conclusively linked with the exanthem (2). In a prospective case-control study from Pediatric Dermatology in 2000, the authors found no statistically significant differences between cases and controls for multiple viruses and bacteria investigated as possible etiologic agents (3).The exanthem also appears to have seasonality, with predominance of cases in late winter and early spring (2). Moreover, the common association with mild fever, upper respiratory and/or gastrointestinal symptoms suggests a viral trigger.

Differential Diagnosis

The most common initial misdiagnosis is a contact dermatitis. The differential diagnosis also includes pityriasis rosea, scarlet fever, miliaria, erythema infectiosum, tinea corporis, and Gianotti-Crosti syndrome (4). Pityriasis rosea(PR) may persist for 2-3 months and clinically overlaps with unilateral laterothoracic exanthema, but in PR the eruption is symmetric with a predilection for involvement of the lower torso and is often preceded by a solitary herald patch. Gianotti-Crosti syndrome tends to involve the extensor surfaces of the arms and leg as well as the face and buttocks, while erythema infectiosum is characterized by a lacy reticulated erythema on the extremities and slapped cheek erythema which waxes and wanes for several months during epidemics which tend to occur in the late spring and early summer. The sandpaper rash of scarlet fever followed 2 weeks later by diffuse desquamation is distinctive, and tinea corporis is usually very localized and intensely pruritic.


Within 2–3 weeks, the eruption displays its greatest intensity followed by a late desquamative phase. Treatment is supportive care. Antihistamines may be beneficial when significant pruritus is present, and moisturizers can be helpful during desquamation. The response to topical corticosteroids is variable (4). Lesions are self-limited and resolve spontaneously within 3–6 weeks of the initial eruption (2). Occasionally the eruption may persist for several months.

Our Patient

The eruption persisted for another 4 weeks and then resolved without treatment. Minimal itching was managed with topical moisturizers and occasional oral antihistamines at bedtime.


A healthy child presenting with a unilateral morbilliform viral exanthem should suggest the diagnosis of self-limited unilateral laterothoracic exanthem.


  1. Paller A, Mancini A. Unilateral Laterothoracic Exanthem. Hurwitz Clinical Pediatric Dermatology, 3rd edition. 2006:436-438.
  2. Nahm W, Paiva C, Golomb C, Badiavas E, Laws W. Asymmetric Periflexural Exanthem of Childhood: A Case Involving a 4-Month-Old Infant. Pediatric Dermatology. 2002;19(5):461-462.
  3. Coustou D, Masquelier B, Lafon M, Labreze C, Roul S, Bioulac-Sage P, Megraud F, Fleury H, Taieb A. Asymmetric Periflexural Exanthem of Childhood: Microbiologic Case-Control Study. Pediatric Dermatology. 2002;17(3):169-173.
  4. McCuaig C, Russo P, Powell J, Pedneault L, Lebel P, Marcoux D. Unilateral Laterothoracic Exanthem: A Clinicopathologic study of forty-eight patients. Journal of the American Academy of Dermatology. 1996;34(6):979-984.




Body Site

Anatomic Depth