Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2024;14(1):e2024013 1 Paradoxical Psoriasis: A Dermoscopic and Histopathologic Teaching Point Marco Adriano Chessa1,2, Luca Rapparini1,2, Federica Filippi1, Carlotta Baraldi1, Bianca Maria Piraccini1, Iria Neri1 1 Dermatology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy 2 Department of Medical and Surgical Sciences, Alma Mater Studiorum University of Bologna, Italy Citation: Chessa MA, Rapparini L, Filippi F, Baraldi C, Piraccini BM, Neri I. Paradoxical psoriasis: A Dermoscopic and Histopathologic Teaching Point. Dermatol Pract Concept. 2024;14(1):e2024013. DOI: https://doi.org/10.5826/dpc.1401a13 Accepted: June 12, 2023; Published: January 2024 Copyright: ©2024 Chessa 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: Luca Rapparini, MD, Dermatology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Department of Medical and Surgical Sciences, Alma Mater Studiorum University of Bologna, Via Massarenti 1, 40138 Bologna, Italy. ORCID 0000-0002- 4029-941X. Phone: +390512144838 E-mail: luca.rapparini2@studio.unibo.it Case Presentation A 50-year-old woman presented an erythematous desquama- tive plantar eruption occurred 6 months prior to the visit (Figure 1A). Several treatments with topical potent cortico- steroids and antimycotics were given in the clinical suspect of dyshidrotic eczema, without improvement. Dermoscopy showed white scales and regularly dis- tributed red dots, a pattern usually detected in psoriasis (Figure 1B) [1]. Histological examination showed parakeratosis, hy- pogranulosis and psoriasiform epidermal hyperplasia and neutrophils in the stratum corneum, forming Munro micro-abscesses, confirming the diagnosis of psoriasis (Figure 1C). A further investigation of medical history revealed that the patient was affected by Crohn disease, and successfully treated with adalimumab in the last 5 years. A diagnosis of paradoxical psoriasis was proposed, and in agreement with the gastroenterologist, biological therapy was switched to ustekinumab. In addition, calcipotriol/betamethasone dipropionate ointment was started. At 3 months of follow- up, the plantar lesions were completely resolved, without Crohn’s disease relapses. Teaching Point Paradoxical psoriasis is a well-documented manifestation in patients with inflammatory bowel disease treated with anti-TNF-α agents [2]. The pathological mechanism of the onset of psoriasis due to anti-TNF-α seems related to the migration of T cells to the skin induced by IFN-α produced by plasmacytoid dendritic cells. Dermoscopy in palmoplantar localization could be crucial for a differential diagnosis: in chronic dyshidrotic eczema yellow scales and brownish dots/globules are usually detected (Figure 1D) corresponding to tiny spongiotic vesi- cles; while psoriasis is characterized by white scales and reg- ular distributed red dots. In these cases, the withdrawal from anti-TNF-α usually induces a complete remission of the skin lesions, thus con- firming a reversible and drug-related side effect. 2 Image Letter | Dermatol Pract Concept. 2024;14(1):e2024013 In our case, given the personal history of Crohn disease, a switch to a biological drug of another class was successfully undertaken. Patient Consent: Informed consent for the use of informa- tion and images has been obtained from the patient. References 1. Çetinarslan T, Türel Ermertcan A, Temiz P. Dermoscopic clues of palmoplantar hyperkeratotic eczema and palmoplantar psoriasis: A prospective, comparative study of 90 patients. J Dermatol. 2020;47(10):1157-1165. DOI: 10.1111/1346-8138.15487. PMID: 32691449. 2. Pugliese D, Guidi L, Ferraro PM, et al. Paradoxical psoriasis in a large cohort of patients with inflammatory bowel disease re- ceiving treatment with anti-TNF alpha: 5-year follow-up study. Aliment Pharmacol Ther. 2015;42(7):880-888. DOI: 10.1111 /apt.13352. PMID: 26235565. Figure 1. (A) Erythematous desquamative plantar eruption with rhagades. (B) Dermoscopy of palmoplantar psoriasis: white scales (white arrows) and regular distributed red dots (red arrows). (C) Histology of palmoplantar psoriasis: parakeratosis, hypogranulosis, psoriasiform epidermal hyperplasia, neutrophil in the stratum corneum, dilated capillaries and perivascular lymphocytes in the dermis (H&E, 10x). (D) Dermoscopy of dyshidrotic eczema: yellow scales (yellow arrows) and brownish dots/globules (brown arrows).