Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2022;12(4):e2022175 1 Lichenoid Keratosis Simulating Melanoma: a Case Report Leire Barrutia1,2, Nelson Lobos1, Josep Malvehy1, Sebastian Podlipnik1 1 Melanoma Unit, Dermatology Department, Hospital Clínic de Barcelona, IDIBAPS, Universitat de Barcelona, Barcelona, Spain. 2 Dermatology Department, Clinical University Hospital of Valladolid, Valladolid, Spain. Citation: Barrutia L, Lobos N, Malvehy J, Podlipnik S. Lichenoid keratosis simulating melanoma: A case report. Dermatol Pract Concept. 2022;12(4):e2022175. DOI: https://doi.org/10.5826/dpc.1204a175 Accepted: January 5, 2022; Published: October 2022 Copyright: ©2022 Barrutia 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: Leire Barrutia, MD, Dermatology Department, Clinical University Hospital of Valladolid – Edificio Rondilla. Calle Rondilla Sta Teresa s/n, 47010, Valladolid, Spain. E-mail: leirebarrutia4@gmail.com Case presentation An 80-year-old male was referred to the Dermatology De- partment for a pigmented lesion on his right arm that had been present for over twenty years but had rapidly grown and become more pigmented in the last three months. Physi- cal examination showed a 10 mm dark, bluish-brown plaque and dermoscopy revealed a multicomponent pattern with multiple colors and pseudopods (Figure 1B). Reflectance confocal microscopy was performed, and the most prom- inent findings were a regular epidermal architecture, rem- nants of cord-like pattern in the dermoepidermal junction, and abundant aggregates of plump-bright cells in the pap- illary dermis, corresponding to melanophages (Figure 1C). An excisional biopsy was performed, and histopathological analysis showed epidermal hyperplasia with hyperkeratosis, vacuolar-interface dermatitis, and a dense dermal infiltrate of melanophages and lymphocytes. SOX10 stain high- lighted dermal melanophage-aggregates (Figure 1, D and E). Therefore, both confocal microscopy and histopathology were compatible with lichen planus-like keratosis (LPLK). Teaching point The diagnosis of seborrheic keratosis is typically straightfor- ward. However, in cases of regression, also known as LPLK, these lesions may mimic melanoma or other malignancies [1]. Dermoscopic findings of lichenoid keratosis change as regression progresses, and several patterns have been described, such as light-brown or gray pseudo-networks, annular-granular structures and blue-gray globules [2]. We present a case in which some of those features were pres- ent, but were accompanied by other structures than have not been described yet in LPLK and that can be very misleading, such as pseudopods and blue-gray veil. Confocal microscopy was particularly useful in this challenging case, and diagno- sis was confirmed by histopathology. 2 Image Letter | Dermatol Pract Concept. 2022;12(4):e2022175 References 1. Ramirez-Fort MK, Al Jalbout S, Kittler H, Pellacani G. Lichenoid keratosis: non-invasive imaging in the setting of diagnostic uncer- tainty. Dermatol Pract Concept. 2013;3(2):63-65. DOI: 10.5826/ dpc.0302a10. PMID: 23785648. PMCID: PMC3663400. 2. Watanabe S, Sawada M, Dekio I, Ishizaki S, Fujibayashi M, Tanaka M. Chronology of lichen planus-like keratosis features by dermoscopy: a summary of 17 cases. Dermatol Pract Con- cept. 2016;6(2):29-35. DOI: 10.5826/dpc.0602a06. PMID: 27222769. PMCID: PMC4866624. Figure 1. (A) Physical examination showed a 10 mm bluish-brown plaque. (B) Dermoscopy revealed a multicomponent pattern with mul- tiple colors, and asymmetrically distributed blue-gray globules. Moreover, diffuse peripheral projections coalescing into pseudopods were observed on the left bottom side, and blue-gray veil and annular-granular structures in the center. (C) Reflectance confocal microscopy showed remnants of cord-like pattern, and aggregates of small-bright particles in the papillary dermis, corresponding to melanophages. (D) Histopathology, H&E 200x. Epidermal hyperplasia with hyperkeratosis, vacuolar-interface dermatitis and a dense dermal infiltrate of melanophages and lymphocytes. (E) SOX10 (Sry-related HMg-Box gene 10), 400x. Absence of melanocytic hyperplasia, and dermal mela- nophage-aggregates can be observed.