Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2024;14(1):e2024016 1 An Unusual Case of Lichen Striatus Onset Under Dupilumab in a Patient With Alopecia Areata Vittorio Tancredi1, Graziella Babino1, Elisabetta Fulgione1, Stefano Caccavale1, Giuseppe Argenziano1 1 Dermatology Unit, Department of Mental and Physical Health and Preventive Medicine, University of Campania Luigi Vanvitelli, Naples, Italy Citation: Tancredi V, Babino G, Fulgione E, Caccavale S, Argenziano G. An Unusual Case of Lichen Striatus Onset Under Dupilumab in a Patient With Alopecia Areata. Dermatol Pract Concept. 2024;14(1):e2024016. DOI: https://doi.org/10.5826/dpc.1401a16 Accepted: May 15, 2023; Published: January 2024 Copyright: ©2024 Tancredi 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: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Vittorio Tancredi, MD, Dermatology Unit, Department of Mental and Physical Health and Preventive Medicine, University of Campania Luigi Vanvitelli, Via Sergio Pansini, 5, 80131 Naples, Italy; phone: +39 3313919797; fax: +39 081 987252; E-mail: tancredivittorio@ymail.com Case Presentation In October 2022 a 15-year-old boy acceded in our Department. He was already our patient for the management of his universal alopecia areata, handled from May 2022 with dupilumab, an anti-IL-4 and IL-13 receptor inhibitor [1]. After 5 months only partial improvement signs of his alopecia areata were detected. However, he showed us a curious skin rash on his lower left limb which had onset in August. Clinical examination revealed pink-red small papules, slighty wrinkled, grouped in plaques and in blaskhoid fashioned distribution, from his left groin to the calf. Due to patient’s parents had refused skin biopsy, a clin- ical diagnosis of lichen striatus (LS) was made (Figure 1). LS is a rare cutaneous eruption of unknown etiology, that has been as- sociated with some conditions like atopic dermatitis and so on. Teaching Point Some authors retained that post zygotic somatic mutations of skin cells may determinate the genesis of a mosaicism, presenting different keratinocyte antigens. A mosaicism is that condition marked by the presence of more than one genetic line as a result of a DNA mutation, in a multicellular organism [2]. A blaskhoid eruption may appear, when this clone is target by a not specific immune system response, probably triggered by unknown factors2. Dupilumab is able to switch the immune response from a Th2 to a Th1 and Th17 pathway which, in our opinion, may induce autoim- mune responses against mosaic cells and thus blaskhoid eruption in predispose patients [1]. 2 Image Letter | Dermatol Pract Concept. 2024;14(1):e2024016 References 1. Kychygina A, Cassagne M, Tauber M, et al. Dupilumab-Associated Adverse Events During Treatment of Allergic Diseases. Clin Rev Allergy Immunol. 2022;62(3):519-533. DOI: 10.1007 /s12016-022-08934-0. PMID: 35275334. Figure 1. (A, B) papules and plaques in blaskhoid distribution, from the left calf to the groin. (C) dermatoscopic evaluation displayed papules and plaques characterized by dotted and linear vessels on a pink-yellow background and faint erythema. 2. Darsha AK, Cohen PR. Blaschkolinear Acquired Inflammatory Skin Eruption (BLAISE): Case Report of a Young Man Whose Dermatosis had Features of Lichen Striatus and Blaschkitis. Cureus. 2020;12(10):e10785. DOI: 10.7759/cureus.10785. PMID: 33154852. PMCID: PMC7606174.