Case Report: Primary cutaneous infection caused by Microascus trigonosporus

Background Microascus trigonosporus is an emerging opportunistic filamentous fungus, with most reported cases involving invasive pulmonary infections in solid organ transplant recipients. Worldwide, cutaneous infections caused by this organism are extremely rare. This case highlights an unusual presentation of primary cutaneous infection in a non-transplant host. Methods We report a case of a 67-year-old woman who presented with progressive skin erythema and pustules for two months, unresponsive to topical halometasone. Her medical history included glaucoma, hypertension, and coronary heart disease. The diagnostic workup included microscopic examination of skin lesion scrapings, skin biopsy for histopathology, fungal culture, and metagenomic next-generation sequencing (mNGS) for pathogen identification. The patient was treated sequentially with oral fluconazole for 2 weeks, followed by itraconazole for 8 weeks, and was followed up for 1 year. Results Microscopic examination of skin scrapings revealed abundant, branched, and septate fungal hyphae. Skin biopsy revealed chronic inflammation with neutrophil infiltration in the superficial dermis. Fungal culture results were positive, and the isolate exhibited morphological features consistent with the genus Microascus . The pathogen was definitively identified as M. trigonosporus using mNGS. The skin lesions completely resolved after sequential antifungal therapy (fluconazole for 2 weeks, followed by itraconazole for 8 weeks). No drug-related adverse events were observed, and no recurrence was noted during the 1-year follow-up. Conclusion This case expands the disease spectrum of M. trigonosporus , demonstrating that primary cutaneous infections can occur in non-transplant hosts. mNGS facilitates the rapid identification of rare filamentous fungi in chronic, undiagnosed skin lesions, enabling earlier and more precise diagnoses.