Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2025;15(1):4659 1 Pseudoxanthomatous Mastocytosis: A Rare Variant in a Hispanic Male Anabell Andrea Lima-Galindo1, Oralia Mariela Cárdenas-Torres1, Mariela Irabien-Zúñiga1, Alejandra Perales-González1, Jorge Ocampo-Candiani1, Erika Alba-Rojas1 1 Universidad Autónoma de Nuevo León, Dermatology Department, Hospital Universitario “Dr. José Eleuterio González,” Monterrey, Nuevo León, México Citation: Lima-Galindo AA, Cárdenas-Torres OM, Irabien-Zúñiga M, Perales-González A, Ocampo-Candiani J, Alba-Rojas E. Pseudoxanthomatous Mastocytosis: A Rare Variant in a Hispanic Male. Dermatol Pract Concept. 2025;15(1):4659. DOI: https://doi. org/10.5826/dpc.1501a4659 Accepted: September 30, 2024; Published: January 2025 Copyright: © González-Valdés 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: Erika Alba-Rojas, Department of Dermatology, Hospital Universitario ‘Dr. José Eleuterio Gonzàlez’, Universidad Autónoma de Nuevo León, Monterrey, México. Av. Madero and Gonzalitos S/N 64460 Mitras Centro, Monterrey, Mexico. Phone: +52 8183481465 ext 344. E-mail: eri9ar@gmail.com Case Presentation A 34-year-old Hispanic man presented to the dermatology de- partment with multiple itchy yellowish nodules on his trunk and extremities (Figures 1A and B), which had appeared at six months of age. No abnormalities were found on general lab- oratory tests, and serum tryptase was requested. Dermoscopy revealed a pigment network and brown streaks on a yellowish pink background (Figure 1C). During the physical examination, rubbing the lesions induced only erythema, indicating a nega- tive Darier sign. Histopathology showed a diffuse infiltration of mast cells in the dermis (Figure 1D), confirmed by Giemsa staining (Figure 1E) and CD117 immunohistochemistry (Figure 1F), which demonstrated a density of 70 mast cells per mm². The diagnosis of pseudoxanthomatous mastocytosis was estab- lished, and treatment was initiated with oral antihistamines. Teaching Point Pseudoxanthomatous mastocytosis (PXM) is an extremely rare variant of mastocytosis, first described in 1875 as “xanthelasmoid mastocytosis.” It is a form of diffuse cu- taneous mastocytosis characterized by multiple yellow- ish papules and flat nodules resembling xanthomas [1]. Notably, rubbing frequently triggers erythema without wheals (negative Darier sign) in this variant [1]. Histopatho- logically, PXM shows dermal mast cell infiltration, similar to other forms, but it is distinguished by a deeper infiltration, potentially contributing to the yellowish color of the lesions [2]. Clinical features and histopathological findings confirm the diagnosis. Treatment options include antihistamines, avoidance of triggers, topical or systemic steroids, photo- therapy, and interferon [1]. 2 Image Letter | Dermatol Pract Concept. 2025;15(1):4659 This case is interesting because it represents a highly uncommon variant, with only a few cases documented in the literature. Moreover, while certain forms of cuta- neous mastocytosis often resolve spontaneously, PXM typically persists into adulthood, as observed in our patient. No  additional systemic involvement has been reported [2]. References 1. Srivastava N, Chand S, Singh S. Pseudoxanthomatous mastocy- tosis. Int J Dermatol. 2008;47(1):50-51. DOI: 10.1111/j.1365 -4632.2007.03358.x 2. Chouk C, Souissi A, Raboudi A, Belkahia A, Boubaker S, Mokni M. Xanthelasmoid mastocytosis: A rare entity. Australas J Dermatol. 2021;62(2):229-230. DOI: 10.1111/ajd.13475 Figure 1. Male patient presenting with multiple yellowish and pink confluent nodules predomi- nantly located on the (A) lower back and (B) extremities. (C) Dermoscopy of the nodules revealed a pigment network and brown streaks on a yellowish pink background. (D) Skin biopsy stained with H&E shows infiltration of mast cells in the dermis (120x magnification). (E) Giemsa stain demon- strating the metachromatic granules of mast cells (200x magnification). (F) Immunohistochemical staining revealed CD117 positive cells (200x magnification), with a mast cell count of 70 per mm².