Unilateral Rash in a Toddler

Correct Answer: E. Unilateral laterothoracic exanthem of childhood (ULE)

Based primarily on the one-sided presentation, the patient was diagnosed with unilateral laterothoracic exanthem of childhood (ULE). The patient’s recent history of an upper respiratory infection supported the rationale of a viral etiology. Serologic testing for specific viruses was not performed because it would not have changed our treatment plan.

One of the most common misdiagnoses of ULE is contact dermatitis. Contact dermatitis can be unilateral like ULE, but it would be significantly more pruritic and typically presents with vesicles and oozing, which is not seen here.¹ Contact dermatitis is one of the most commonly diagnosed dermatological conditions, but it is triggered by exposure to allergenic substances and does not have a viral prodrome.²

The morbilliform appearance of ULE can mimic drug-related eruptions, miliaria, scabies, and atypical pityriasis rosea. These all would be more symmetrical in distribution, and not unilateral like ULE. Regarding pityriasis rosea, ULE does have similarities in seasonality and duration, but it would be more common in school-aged children and young adults.¹

Miliaria is often self-limited, like ULE. It is also known as heat rash or sweat rash and is triggered by blocked eccrine sweat glands.³ A notable diagnostic difference in miliaria compared to ULE is its symmetric distribution and would generally be seen on the neck and upper body.¹

Gianotti-Crosti syndrome could also be mistaken for ULE because it appears in the same age group and is also a papular exanthem. However, Gianotti-Crosti syndrome is symmetric, typically spares the trunk, and most commonly involves the face, buttock, and extensor extremities. It is typically accompanied by lymphadenopathy, with the potential of accompanying hepatosplenomegaly.¹

Treatment and Management. The patient’s condition did not require pharmacologic treatment, but the family was counseled on the use of antihistamines or pramoxine lotion if it became pruritic, and that it was approved to use desonide as needed. The patient’s mother was counseled on the expected course of ULE, that it could last 6 weeks, and may peel as it resolves. The family was reassured that the rash would resolve in that timeframe. The patient was not seen back at the clinic.

Discussion. ULE of childhood, also known as asymmetric periflexural exanthem of childhood, is an uncommon disease, typically affecting children between 1 and 5 years of age. This eruption often begins in the axillary region, then develops into a widespread skin eruption.⁴ The exanthem can also begin in other skin flexures, and has been found to originate from the thigh, flank, and inguinal folds.¹ Spontaneous regression of the exanthem is typically expected to happen between the third and sixth week of the eruption.⁴ As ULE is resolving, the lesions appear dusky and then desquamate. It is important to note that this eruption typically will spare the face, palms, soles, and mucous membranes. Throughout the course of ULE, local lymphadenopathy and pruritus are possible but not required to make a diagnosis.¹

A viral etiology of ULE has been suggested in previous cases, with triggers including adenovirus, parainfluenza virus, parvovirus B19, human herpesvirus 6 and 7, Epstein-Barr virus, and COVID-19.^4,5 Evidence to back up a viral etiology includes upper respiratory tract or gastrointestinal symptoms as a prodromal finding, peaks during the winter and spring months, and the frequent involvement of several children in single family homes.¹

The progression of ULE has been described in three phases before it regresses. The first phase describes the first signs of ULE, which is often a patch of small, papular, pink lesions on one side of the thorax. The second phase describes the inflammatory progression of the initial lesions. In this phase, the most central lesions begin to clear but leave behind a faint brown or violaceous scale. The third phase describes the eruption within 1 to 3 weeks of the initial onset. At this point, similar lesions have spread to the contralateral thorax and extremities with a focus on extensor surfaces. It should also be noted that a pallid halo may surround individual papules of all phases, which can be an important diagnostic feature of the exanthem.⁶

Conclusion. This case report illustrates the clinical presentation and management of unilateral laterothoracic exanthem of childhood. A viral prodrome with a unilateral distribution is strongly indicative of the diagnosis. Although self-limited, the appearance can cause concern for the patient’s family. In a toddler presenting with a unilateral skin eruption, the diagnosis of ULE should be considered.

AUTHORS:
Dana Simon, BS¹ • Michelle Gallagher, DO²

AFFILIATIONS:
¹Osteopathic Medical Student, Michigan State University College of Osteopathic Medicine

²Associate Professor, Michigan State University College of Osteopathic Medicine, Department of Pediatrics

CITATION:
Simon D, Gallagher M. Unilateral rash in a toddler Consultant. Published online XX. doi:XX

Received July 18, 2024. Accepted October 28, 2024.

DISCLOSURES:
The authors report no relevant financial relationships.

ACKNOWLEDGEMENTS:
None.

CORRESPONDENCE:
Dana Simon, BS, Michigan State University College of Osteopathic Medicine, 965 Wilson Road, East Lansing, MI 48824 (Simond10@msu.edu)

References

1. Chaabani M, Souissi A. Asymmetric periflexural exanthem in childhood. StatPearls. Published November 6, 2019. Available from: https://www.statpearls.com (Include direct URL if available).
2. Massochin AR, Oliveira CW de M, Valentim LÁ, et al. Allergic contact dermatitis: Causes, symptoms, and specific therapies. Rev Gestão Socioambiental. 2024;18(8):e06282. doi:10.24857/rgsa.v18n8-057.
3. Guerra KC, Toncar A, Krishnamurthy K. Miliaria. In: StatPearls. Treasure Island, FL: StatPearls Publishing; 2023. Available from: https://www.statpearls.com (Include direct URL if available).
4. Prćić S, Gajinov Z, Radulović A, Matić M, Matić A. Unilateral laterothoracic exanthem: A case report and literature review. Serbian J Dermatol Venereol. 2017;9(2):49-52. doi:10.1515/sjdv-2017-0007.
5. Yelich A, Dazé R, Moon S. An asymmetric morbilliform eruption in an adult male. JAAD Case Rep. 2023;31:142-145. doi:10.1016/j.jdcr.2022.11.037.
6. Laur WE. Unilateral laterothoracic exanthem in children. J Am Acad Dermatol. 1993;29(5):799-800. doi:10.1016/s0190-9622(08)81712-4.

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