Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2025;15(1):4847 1 Reflectance Confocal Microscopy in Tinea Nigra: A Diagnostic Teaching Point Samuel Ibáñez1, Dominga Peirano2, Rosario Agüero2, Cristián Navarrete-Dechent2,3, Álvaro Abarzúa-Araya2,3 1 Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 2 Departamento de Dermatología, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile 3 Unidad de Melanoma y Cáncer de Piel, Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile Citation: Ibáñez S, Peirano D, Agüero R, Navarrete-Dechent C, Abarzúa-Araya A. Reflectance Confocal Microscopy in Tinea Nigra: A Diagnostic Teaching Point. Dermatol Pract Concept. 2025;15(1):4847. DOI: https://doi.org/10.5826/dpc.1501a4847 Accepted: August 26, 2024; Published: January 2025 Copyright: © Ibáñez 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: Álvaro Abarzúa-Araya, MD, IFAAD, Department of Dermatology, Escuela de Medicina, Pontificia Universidad Católica de Chile, Diagonal Paraguay 362, 6th floor, Santiago, Chile 8330077. E-mail: alvaroabarzuaaraya@gmail.com Case Presentation A 24-year-old woman presented with a single asymptom- atic brown macule located on the sole of the right foot (Figure 1A) after returning from a trip to Brazil. Dermos- copy showed linear and dotted brown superficial struc- tures with homogeneous distribution, which did not follow furrows or ridges, a pattern compatible with tinea nigra (TN) (Figure 1B). Reflectance confocal microscopy (RCM) showed the presence of septate partitioned hyphae in stra- tum corneum (Figure 1C and D). Direct KOH test showed septate hyphae, confirming the diagnosis of TN. The lesion resolved completely after a course of topical terbinafine 1% twice daily for three weeks. Teaching Point TN is an uncommon superficial mycosis caused by Hortaea werneckii characterized by deeply pigmented macular non- scaly patches. It can be misdiagnosed as a malignant melanoma or a junctional melanocytic nevus based on clinical features alone [1]. RCM is a noninvasive imaging tool that allows for the observation of tissues with in vivo quasi- histological resolution. In the case of TN, it is possible to observe the characteristic filamentous, septate, elongated branching structures that correspond to the hyphae in the stratum cor- neum [2]. As noninvasive tools such as RCM become more readily available, we believe it is necessary to open discus- sion regarding the use of them in daily dermatology practice 2 Image Letter | Dermatol Pract Concept. 2025;15(1):4847 beyond skin cancer for the diagnosis of viral, fungal, and ectoparasitic infections, as it allows more precise diagnos- tics, reduces time and costs, and avoids potentially harmful invasive procedures. References 1. Xavier MH, Ribeiro LH, Duarte H, Saraça G, Souza AC. Der- matoscopy in the diagnosis of tinea nigra. Dermatol Online J. 2008;14(8):15. 2. Navarrete-Dechent C, Bajaj S, Marghoob AA, Marchetti MA. Rapid diagnosis of tinea incognito using handheld reflectance confocal microscopy: a paradigm shift in dermatology? Mycoses. 2015;58(6):383-386. DOI:10.1111/myc.12333. Figure 1. (A) Clinical photograph, (B) dermoscopy, and (C, D) reflectance confocal micros- copy of the lesion. In (A) a brown macule of 10 mm in diameter is observed. In (B) there are linear and dotted brown superficial structures with homogeneous distribution which do not follow grooves or ridges. In (C) there are septate hyphae septate in stratum corneum, with higher magnification and marked with arrows in (D).