Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2023;13(3):e2023164 1 Abrupt Bullous Cutaneous Eruption After Application of Tacrolimus Ointment and Sun Exposure Cristina Beatrice Spigariolo1, 2, Francesca Barei1, 2, Angelo Valerio Marzano1,2, Silvia Ferrucci1 1 Unit of Dermatology, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy 2 Department of Pathophysiology and transplantation, University of Milan, Milan, Italy Citation: Spigariolo CB, Barei F, Marzano AV, Ferrucci S. Abrupt Bullous Cutaneous Eruption After Application of Tacrolimus Ointment and Sun Exposure. Dermatol Pract Concept. 2023;13(3):e2023164. DOI: https://doi.org/10.5826/dpc.1303a164 Accepted: January 10, 2023; Published: July 2023 Copyright: ©2023 Spigariolo 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 work was supported by Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico of Milan/Italian Ministry of Health (RC2023). Competing interests: None. Authorship: All authors have contributed significantly to this publication. Acknowledgement: The patient in this manuscript have given written informed consent to publication of her case details. Corresponding author: Cristina B. Spigariolo, Unit of Dermatology, Via Pace 9, 20122 Milan (Italy). E-mail: cristina.spigariolo@unimi.it Case Presentation A 46-year-old woman complained of an acute bullous der- matitis, which appeared after sun exposure, localized in the areas where she applied tacrolimus 0.03% ointment (for her vitiligo) in the previous days. After about 20 minutes of solar exposure (using sunscreen SPF50+), she felt a burn- ing sensation, followed by the appearance of vesiculobul- lous lesions on the abdomen, groins and axilla (Figure 1A). No other topical or systemic drugs had been used. She was treated with Prednisone 25 mg/day tapered in 15 days with scarring resolution in eight weeks (Figure 1B)]. After clinical resolution, broadband UV) photopatch testing (PPT) was performed. The patient sunscreen and the Tac- rolimus ointment 0.03% used by the patient, together with Chemotechnique-Diagnostics® photopatch series were tested. An erythematous reaction was seen on the UVA- irradiated skin where tacrolimus 0.03% ointment was ap- plied (Figure 1C). Based on medical history, clinical ex- amination and the results of the PPT, we made diagnosis of photosensitive reaction. The patients’ medical history (acute onset, clinical bullous aspects and lack of prior sensitization) was better compatible with a hyperacute phototoxic reaction induced by the Tacrolimus ointment 0.03% rather than a photoallergic one [1]. Teaching Point Even if tacrolimus ointment is widely used, only one case of contact dermatitis was described [2]. To the best of our knowledge, this is the first case of bullous reaction to Tacro- limus ointment after sun exposure. 2 Image Letter | Dermatol Pract Concept. 2023;13(3):e2023164 Figure 1. (A) Erythematous-bullous eruption localized on abdomen, groins and axilla characterized by blisters of 1-6 cm in di- ameter and serous content. (B) Scarring outcome after 8 weeks. (C) Results of photopatch-testing: an erythematous reaction was seen on UVA-irradiated-skin (left side of the patient’s back) where tacrolimus 0.03% ointment was applied, no reactions were present on both irradiated and non-irradiated areas where sunscreen and Chemotechnique Diagnostics® photopatch testing series were applied. Image Letter | Dermatol Pract Concept. 2023;13(3):e2023164 3 References 1. Monteiro AF, Rato M, Martins C. Drug-induced photosensi- tivity: Photoallergic and phototoxic reactions. Clin Dermatol. 2016;34(5):571-581. DOI: 10.1016/j.clindermatol.2016.05.006. PMID: 27638435. 2. Shaw DW, Eichenfield LF, Shainhouse T, Maibach HI. Aller- gic contact dermatitis from tacrolimus. J Am Acad Dermatol. 2004;50(6):962-965. DOI:10.1016/j.jaad.2003.09.013. PMID: 15153904.