Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2023;13(2):e2023099 1 Pustular Psoriasis Triggered by a Subcutaneous Tissue Expander Mario Alessandri-Bonetti1, Claudio Conforti2, Francesco Amendola1, Riccardo Carbonaro1, Manuela Cirami3, Luca Vaienti1 1 Department of Reconstructive and Aesthetic Plastic Surgery, University of Milan, I.R.C.C.S. Istituto Galeazzi, Milan, Italy 2 Dermatology Clinic, Maggiore Hospital of Trieste, Trieste, Italy 3 Department of Pathology, I.R.C.C.S. Policlinico San Donato, Piazza Edmondo Malan, San Donato Milanese, Italy Citation: Alessandri-Bonetti M, Conforti C, Amendola F, Carbonaro R, Cirami M, Vaienti L. Pustular Psoriasis Triggered by a Subcutaneous Tissue Expander. Dermatol Pract Concept. 2023;13(2):e2023099. DOI: https://doi.org/10.5826/dpc.1302a99 Accepted: September 23, 2022; Published: April 2023 Copyright: ©2023 Alessandri-Bonetti 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: Mario Alessandri-Bonetti, MD, Department of Reconstructive and Aesthetic Plastic Surgery, University of Milan, IRCSS Istituto Galeazzi, Via Riccardo Galeazzi 4 - 20161 Milan, Italy. Telephone number: +393385033483; E-mail: m.alessandribonetti@gmail.com Case Presentation An African 50-year-old female presented to our department complaining of retracting, painful and dystrophic scarring caused by a previous childhood burn in the right pectoral area. Past medical history was unremarkable. We chose a two-step approach to treat her burn sequelae. First, we inserted a 400-cc silicone smooth rectangular tissue expander (Mentor, Irvine, USA) in the right suprascapular area. The expander was progressively filled during ambu- latory visits. Secondly, three months later, the dystrophic area was excised and reconstruction was performed using the expanded skin flap. At 12-months follow-up, the patient complained of itch above the advancement flap. We noticed an indurated purple plaque within the distal part of the flap, measuring 15x16 cm and surrounded by erythematous bor- ders (Figure 1A). Multiple pruritic pustules were noted in the upper arms, abdomen and dorsum (Figure 1B). Biopsies of the right pectoral plaque and of a left supraclavicular pustule were taken. Histology revealed parakeratosis, acanthosis, epidermal spongiotic pustules, perivascular inflammatory infiltrate with neutrophils in the epidermis and psoriasiform hyperplasia. Although the negative family history of the patient, our findings were compatible with pustular psoriasis (Figure 1, C and D). Teaching Point Pustular psoriasis (PP) is clinically characterized by sterile pustules corresponding to a neutrophilic infiltrate in the dermis. Usually, PP affects palms and soles while sometimes it may present in a generalized form associated with systemic symptoms. We hypothesized that the keratinocytes stretching and skin insult provoked by tissue expansion could have triggered the development of cutaneous psoriasis presenting as a plausible Koebner phenomenon [1,2]. 2 Image Letter | Dermatol Pract Concept. 2023;13(2):e2023099 References 1. Okamoto T, Ogawa Y, Kinoshita M, et al. Mechanical stretch- induced ATP release from keratinocytes triggers Koebner phe- nomenon in psoriasis. J Dermatol Sci. 2021;103(1):60-62. DOI: 10.1016/j.jdermsci.2021.06.001. PMID: 34187740 2. Qiao P, Guo W, Ke Y, et al. Mechanical Stretch Exacerbates Pso- riasis by Stimulating Keratinocyte Proliferation and Cytokine Production. J Invest Dermatol. 2019;139(7):1470-1479. DOI: 10.1016/j.jid.2018.12.019. PMID: 30641039 Figure 1. (A) Hyperchromic psoriatic plaque in the right pectoral area, developed above the expanded skin flap. (B) Multiple psoriatic pustules developed above abdominal area and upper arms. (C) Psoriasiform acanthosis and thinning of suprapapillary plates. Mild inflam- matory infiltrate (H&E, x10). (D) Subcorneal pustules, parakeratosis and hypogranulosis. Mild inflammatory perivascular and interstitial infiltrate composed predominantly of lymphocytes (H&E, x20).