Dermatology: Practical and Conceptual Research Letter | Dermatol Pract Concept. 2025;15(3):5302 1 Black Superficial Onychomycosis Caused by Neoscytalidium Dimidiatum: A Clinical Overview Hugo Monteiro Faver1, Aline Barbosa de Almeida1, João Paulo Monteiro Yamagata1, Dávson Aguilar Guimarães1, Paula Sá1, Danilo Luis Boechat Marins1 1 Department of Tropical Dermatology, Central Army Hospital, Rio de Janeiro, Brazil Key words: Superficial onychomycosis, Dematiaceous fungus, Neoscytalidium dimidiatum Citation: Faver HM, Almeida AB, Yamagata JPM, Guimarães DA, Sà P, Boechat Marins DL. Black Superficial Onychomycosis Caused by Neoscytalidium Dimidiatum: A Clinical Overview. Dermatol Pract Concept. 2025;15(3):5302. DOI: https://doi.org/10.5826/ dpc.1503a5302 Accepted: February 18, 2025; Published: July 2025 Copyright: ©2025 Faver 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: Hugo Monteiro Faver, MD, Department of Tropical Dermatology, Central Army Hospital, R. Francisco Manuel, 126 - Benfica, Rio de Janeiro - RJ, 20911-270. Orcid ID: 0009-0004-5405-612X. E-mail: hmfaver@hotmail.com Introduction Dematiaceous fungi cause several diseases in humans. Spe- cies identification can be a challenge, since colonies do not always grow in conventional culture media, and even when they do, identification can be impaired due to the atypical appearance, making it necessary to resort to other methods for diagnosis [1,2]. This case highlights an unusual presentation of a rare su- perficial onychomycosis in an elderly patient and illustrates the role of advanced diagnostic methods in identifying rare fungal pathogens. Case Presentation During a routine dermatological examination, a 71-year-old Caucasian man with a history of frequent beach exposure and recreational fishing presented with a pigmented alter- ation on the third toenail of his left foot (Figure 1A). He had no known comorbidity or history of immunosuppressive conditions that could predispose him to fungal infections. On dermatological examination, there was an irregular superficial brownish pigmentation of the nail plate. There was no evidence of subungual hyperkeratosis and periun- gual inflammation, and fingernails were spared. The rest of the mucocutaneous examination was noncontributory. The patient reported occasionally rubbing the nail surface to re- move the discoloration, but the pigmentation would recur within weeks. Dermoscopy revealed an asymmetric, reticu- lated brown pattern (Figure 1B). Based on the suspicion of superficial onychomycosis, a direct scraping was performed on the nail plate, removing all brownish material. The collected specimen was then processed for direct my- cological examination (DME) and cultured on Sabouraud and Mycosel media. DME showed septate branched brown hyphae. Culture yielded a cottony, loose, disorganized col- ony with a black surface and reverse, consistent with a dematiaceous fungus (Figure 2). Microculture did not reveal reproductive structures, thus preventing phenotypic charac- terization. To further clarify the species, MALDI-TOF mass 2 Research Letter | Dermatol Pract Concept. 2025;15(3):5302 spectrometry was utilized, which identified Neoscytalidium dimidiatum as the causative agent. No type of specific antifungal treatment was necessary, as mechanical removal was effective for the patient to re- main free of the fungus. The patient was also advised on how to take care of local humidity and take care of closed shoes. Conclusion This case illustrates an unusual presentation of superficial black onychomycosis, a form of onychomycosis rarely re- ported in the literature [3]. Dermoscopy helped rule out un- gual melanoma, and species identification was not possible after colony growth, making it necessary to employ other methods for the correct diagnosis and management of the case. This case emphasizes the importance of dermoscopy and advanced mycological techniques, such as MALDI-TOF, in diagnosing atypical presentations of superficial onycho- mycosis, particularly with dematiaceous fungi like Neoscy- talidium dimidiatum. References 1. Revankar SG. Dematiaceous fungi.  Mycoses. 2007;50(2):91- 101. DOI:10.1111/j.1439-0507.2006.01331.x 2. Singh A, Singh PK, Kumar A, et al. Molecular and Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry- Based Characterization of Clinically Significant Melanized Fungi in India.  J Clin Microbiol. 2017;55(4):1090-1103. DOI:10.1128/JCM.02413-16 3. Di Chiacchio N, Noriega LF, Gioia Di Chiacchio N, Ocampo- Garza J. Superficial black onychomycosis due to Neoscytalid- ium dimidiatum.  J Eur Acad Dermatol Venereol. 2017;31(10): e453-e455. DOI:10.1111/jdv.14273 Figure 2. (A) Septate branched brown hyphae were observed on direct mycological examination. (B) The culture shows a cottony, loose, disorganized colony with a black surface and black reverse, characteristic of a dematiaceous fungus. Figure 1. (A) Irregular superficial brownish pigmentation on the nail plate of the left third toe. (B) Asymmetric brownish reticular pattern observed on dermoscopy.