Pyrenochaeta unguis-hominis-associated fungal keratitis: A rare case report with in vivo confocal microscopy findings.

Purpose: Pyrenochaeta unguis-hominis, also known as Neocucurbitaria unguis-hominis, is a rare fungal pathogen typically isolated from skin and nail infections. Recently, it has been identified as a cause of fungal keratitis, particularly among contact lens wearers. This case report documents the occurrence of Pyrenochaeta unguis-hominis keratitis in Austria and the visualization of changes in the corneal stroma using in vivo confocal microscopy (IVCM). Observations: A 48-year-old female patient presented with severe photophobia and acute pain in her left eye, following extended wear of soft contact lenses. Initial examination revealed a central corneal infiltrate. IVCM was performed prior to corneal scraping, which was then sent for direct staining, culture, and next-generation sequencing (NGS) and identified Pyrenochaeta unguis-hominis and Streptococcus oralis. Treatment included hourly topical voriconazole 2 %, natamycin 5 % and vancomycin 2.5 %, with additional epithelial debridement to enhance drug penetration. IVCM imaging allowed for real-time visualization and tracking of structures with the appearance of fungal hyphae, guiding the treatment course. Over several months, IVCM demonstrated a reduction in these structures, and the patient's condition stabilized, resulting in improved corneal clarity and Best Corrected Distance Visual Acuity from 0.8 to 0.9 (Snellen decimal scale). Conclusions and importance: This case contributes to the limited clinical literature on Pyrenochaeta unguis-hominis-associated keratitis and includes IVCM imaging of a cornea with this rare infection. While IVCM provided early, non-invasive visualization of stromal changes, definitive diagnosis was achieved through molecular testing. A conservative treatment regimen with topical antifungals and epithelial debridement was effective, emphasizing the importance of rapid diagnostics and targeted therapy in managing rare corneal infections.