Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2025;15(3):5370 1 Unilateral Laterothoracic Exanthem in an Adult Following Recombinant Zoster Vaccination Xinjin Liu1,2, Deyu Song1,2, Xian Jiang1,2 1 Department of Dermatology, West China Hospital, Sichuan University, Chengdu, China 2 Laboratory of Dermatology, Clinical Institute of Inflammation and Immunology, Frontiers Science Center for Disease-related Molecular Network, West China Hospital, Sichuan University, Chengdu, China Key words: Unilateral laterothoracic exanthem, ULE, Zoster vaccine adult, Herpes zoster vaccination, Recombinant zoster vaccine side effects Citation: Liu X, Song D, Jiang X. Unilateral Laterothoracic Exanthem in an Adult Following Recombinant Zoster Vaccination. Dermatol Pract Concept. 2025;15(3):5370. DOI: https://doi.org/10.5826/dpc.1503a5370 Accepted: January 13, 2025; Published: July 2025 Copyright: ©2025 Liu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: This study was funded by the National Natural Science Foundation of China (82273559). Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Prof. Xian Jiang, Department of Dermatology, West China Hospital, Sichuan University, No. 37 Guoxue Xiang, Chengdu, China, 610041. ORCID: 0000-0001-5109-6055. E-mail: jiangxian@scu.edu.cn Introduction Unilateral laterothoracic exanthem (ULE) is a self-limiting unilateral rash with a suspected viral etiology [1]. In chil- dren, it is often termed asymmetric periflexural exanthem of childhood (APEC). Herein, we present an adult case of ULE following recombinant zoster vaccination. Case Presentation A 57-year-old male presented with a red eruption on the right side of his trunk for 10 days, with mild pruritus but no other discomfort. He had received a recombinant herpes zoster vaccine in his upper right arm two weeks before rash onset. One day post-vaccination, he experienced myalgia and a fever of 38° C, both resolving spontaneously within five days. Subsequently, a rash rapidly developed and spread unilaterally to the right lateral trunk. Loratadine was taken but did not improve symptoms. Physical examination revealed diffuse erythematous papules on his right lateral trunk, with no involvement of other body areas (Figure 1, A and B). Complete blood count, C-reactive protein, and erythrocyte sedimentation rate were within normal limits. Serological tests for COVID-19 and in- fluenza were negative. The diagnosis of ULE was considered. The patient declined a skin biopsy. Remarkably, the lesions resolved within one week without further treatment. Con- sidering the rash distribution, the vaccination history, and the self-limiting course, a diagnosis of ULE was established. Conclusion ULE typically presents with a unilateral erythematous rash originating near the axilla or groin and spread along the af- fected side [1]. In children aged 1–5 years, this condition is commonly referred to as APEC. ULE is generally self-limiting, with a typical duration of 3–6 weeks, and may be accompa- nied by pruritus or mild lymphadenopathy in about 50% of 2 Research Letter | Dermatol Pract Concept. 2025;15(3):5370 cases [2]. Some may also develop dry skin, post- inflammatory hyperpigmentation, and other systemic symptoms, but these usually resolve quickly [2]. Although its etiology re- mains unclear, associations with viral infections and vac- cinations, including COVID-19, have been reported [1,3]. In our case, the patient developed ULE ipsilateral to the re- combinant herpes zoster vaccine injection site. While previous reports have highlighted injection site re- actions, and systemic symptoms as common adverse effects, the occurrence of a rash is rare [4]. The vaccine contains G-protein derived from varicella-zoster virus along with an adjuvant [5]. Most injection-site adverse reactions reported were associated with the adjuvant component [5]. Since the etiology of ULE in previous studies was linked to the viral component, the role of the G-protein in zoster vaccine re- mains unclear. The diagnosis of ULE is primarily clinical, with labora- tory tests typically within normal ranges. Skin biopsy is not required as histological changes are non-specific [2]. Nota- bly, the unilateral distribution of the rash may complicate its association with vaccination or viral infections, potentially leading to misdiagnosis. The potential differential diagnoses include allergic contact dermatitis, superficial fungal infec- tions, and granular parakeratosis [1,2]. Treatment is mainly symptomatic due to its self-limiting nature. This case represents a report of adult ULE following re- combinant herpes zoster vaccination. Clinicians should rec- ognize ULE’s distinct rash and potential triggers. As herpes zoster vaccination becomes more widespread, monitoring for adverse effects is essential. Acknowledgment: This study was supported by the National Natural Science Foundation of China (82273559). Ethics Statement and Informed Consent: This study was ap- proved by the Ethics Committee Biomedical Research, West China Hospital of Sichuan University. We have received and archived written patient consent. References 1. Chuh A, Zawar V, Sciallis GF, Kempf W, Lee A. Pityriasis Rosea, Gianotti-Crosti Syndrome, Asymmetric Periflexural Exanthem, Papular-Purpuric Gloves and Socks Syndrome, Eruptive Pseudo- angiomatosis, and Eruptive Hypomelanosis: Do Their Epidemi- ological Data Substantiate Infectious Etiologies? Infect Dis Rep. Mar 21 2016;8(1):6418. DOI:10.4081/idr.2016.6418. PMID: 27103975 2. Duarte AF, Cruz MJ, Baudrier T, Mota A, Azevedo F. Unilateral laterothoracic exanthem and primary Epstein-Barr virus infec- tion: case report. Pediatr Infect Dis J. Jun 2009;28(6):549-50. DOI:10.1097/INF.0b013e318193eca7. PMID: 19483526 3. Sechi A, Bassi A, Mazzatenta C, et al. Covid-19 and Covid-19 vaccine can slide along sides: a report of two cases of unilateral periflexural exanthema. J Eur Acad Dermatol Venereol. Aug 2022;36(8):e595-e596. DOI:10.1111/jdv.18093. PMID: 35305031 4. James SF, Chahine EB, Sucher AJ, Hanna C. Shingrix: The New Adjuvanted Recombinant Herpes Zoster Vaccine. Ann Pharma- cother. Jul 2018;52(7):673-680. DOI:10.1177/10600280187 58431. PMID: 29457489 5. Jeong SK, Ham SJ, Baek SH, et al. Lipo-pam™ adjuvanted her- pes zoster vaccine induces potent gE-specific cellular and hu- moral immune responses. NPJ Vaccines. Aug 17 2024;9(1):150. DOI:10.1038/s41541-024-00939-4. PMID: 39154056 Figure 1. Clinical image showing multiple erythematous papules diffusely distributed over the right lateral trunk, with no involvement of the contralateral side or other regions.