Neoscytalidium dimidiatum: a rare locally acquired deep cutaneous infection in a renal transplant recipient

Sir, A 76-year-old man from Gran Canaria underwent renal transplantation in May 2022 for chronic renal insufficiency and was maintained on tacrolimus, mycophenolate mofetil, and prednisone. In November 2024, he developed painful, progressive ulcerative and suppurative lesions on his right forearm with edema and blackish crusts after what the patient himself described as a ‘mild trauma caused by a rose bush at his home,’ which resulted in a superficial erosion on the distal forearm. No significant bleeding or systemic symptoms were reported at that time (Figure 1A).  He reported no international travel. Histological diagnosis of deep soft-tissue invasion was performed through visualization of septate hyphae extending down to the hypodermis using PAS and Grocott-Gomori stains. Cultures on Sabouraud Dextrose Agar with chloramphenicol at 28°C and 37°C yielded Neoscytalidium dimidiatum after 4 days, identified by macroscopic (dark, woolly colonies) and microscopic (arthroconidia and hyphae in lactophenol cotton blue; Figure 2) features, confirmed by MALDI-TOF MS (Bruker Daltonics™) and validated at the National Mycology Reference Center (ISCIII, Madrid).  Antifungal susceptibility testing (EUCAST v10.0) revealed minimum inhibitory concentration (MIC) values of liposomal amphotericin B 0.03 mg/L, terbinafine 0.5 mg/L, voriconazole 2 mg/L, itraconazole >8 mg/L, and caspofungin 4 mg/L [1].  Empirical treatment was initiated in December 2024 with oral terbinafine (250 mg every 48 hours, adjusted for renal function: creatinine 2.14 mg/dL, GFR 29 mL/min), followed by a switch to oral caspofungin (70 mg loading dose, then 50 mg/day) and discontinuation of mycophenolate mofetil due to lack of clinical response. The lesions showed mild improvement (Figure 1B); however, therapy was subsequently changed to liposomal amphotericin B (300 mg/day) after obtaining the antifungal susceptibility results, which showed greater sensitivity of the isolate to amphotericin B, and the treatment was therefore adjusted, switching to amphotericin B in order to optimize therapeutic efficacy [2].  By February 2025, voriconazole (200 mg every 12 hours) was initiated for maintenance, with tacrolimus monitoring for interactions, resulting in near-complete resolution with minimal hyperpigmentation (Figure 1C) and culture-negative follow-up biopsies.  Although multiple surgical debridements of necrotic areas were performed, extensive surgical excision was not pursued due to the large surface involved, affecting the entire dorsal aspect of the forearm. In the absence of fever, systemic symptoms, or elevated acute-phase reactants in blood tests, a multidisciplinary team (nephrology, dermatology, and infectious diseases units) decided not to conduct staging studies at the initial timepoint. This case, adhering to CARE guidelines with ethical approval (CHUIMI-2024-112, October 15, 2024) and informed consent, highlights N. dimidiatum as an opportunistic pathogen in transplant recipients. A 2025 systematic review identified only seven deep cutaneous and seven invasive cases globally over 25 years, mostly in tropical settings [3]. European reports of invasive infections are limited, such as a French series of five invasive cutaneous cases in renal transplant recipients (2001–2011), all linked to tropical origins and travel [4]. Published superficial infections in Europe are often imported [5], including four cases in Spain (onychomycosis and tinea pedis linked to South America) [6], 18 dermatomycoses in Switzerland (2009–2018, associated with migrant origins from Africa and Asia) [5], and superficial mycoses in French Guiana (2006–2009, with N. dimidiatum in onychomycoses) [7].  The absence of travel in this case suggests local acquisition, possibly influenced by Gran Canaria’s subtropical climate and ongoing warming trends facilitating fungal adaptation [8]. Diagnosis relied on culture, microscopy, and susceptibility testing, which helps explain initial terbinafine failure due to poor deep penetration and caspofungin’s suboptimal MIC, while amphotericin B and voriconazole aligned with reported efficacy [9]. Reduction of immunosuppression was key, mirroring successes in the French series [4] without the dissemination seen in some fatal cases [10]. Strengths include comprehensive diagnostics and multidisciplinary management; limitations are the single-case nature, lack of standardized breakpoints, and unconfirmed environmental source.  This report emphasizes the need for heightened suspicion of N. dimidiatum in non-endemic Europe, even without travel, and calls for susceptibility-guided therapy, immunosuppression modulation, and studies on climate-related fungal shifts to inform clinical practice.  Acknowledgments The authors would like to express their sincere gratitude to Dr. Ana Alastruei (CNM–ISCIII) for performing the confirmation and antifungal susceptibility testing of the isolate, whose expertise greatly contributed to the accuracy and quality of this work. Funding None to declare. Author contributions Conceptualization, L.R.R., A.S.R., D.A.R., and O.R.L.; methodology, L.R.R., and D.A.R.; validation, L.R.R., A.S.R., D.A.R., and O.R.L.; formal analysis, L.R.R., and D.A.R.; investigation, L.R.R., and A.S.R.; resources, L.R.R., and D.A.R.; data curation, L.R.R., and D.A.R.; writing—original draft preparation, L.R.R., and A.S.R.; writing—review and editing, D.A.R., and O.R.L.; visualization, L.R.R.; supervision, D.A.R., A.S.R., and O.R.L.; project administration, L.R.R., and A.S.R.; microbiological analysis and strain typing, D.A.R. and L.R.R. All authors have read and agreed to the published version of the manuscript. Conflict of interests The authors declare no conflicts of interest. 

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