Possibly the first case of onychomycosis by Fusarium lactis: Case presentation and literature review of onychomycosis by Fusarium species.

Fusarium species (spp.) is frequently found in soil and plant residues and on plant bodies in all climatic zones worldwide. Although there have been few reports of onychomycosis caused by Fusarium spp., it is characterized by drug sensitivity and other characteristics. Here, we report what may be the first case of onychomycosis caused by Fusarium lactis. We analyzed the mycology and characterized previously reported cases of onychomycosis caused by Fusarium spp. A 73-year-old otherwise healthy woman presented with discoloration and thickening of her right thumbnail with paronychia. Direct microscopy revealed unevenly swollen hyphae, and a Grocott-stained nail specimen showed septate hyphae. Based on the morphological features and gene analysis of fungus isolated from the nail, we diagnosed onychomycosis caused by F. lactis belonging to Fusarium fujikuroi species complex. Partial nail removal and topical application of 1% luliconazole solution resolved the condition in 6 months. Minimum inhibitory concentrations for isolated F. lactis showed high sensitivity to luliconazole but not itraconazole or terbinafine. The isolated F. lactis was temperature-sensitive. A search of the literature revealed 57 cases of onychomycosis caused by Fusarium spp. with delineated clinical characteristics. Since those cases were investigated using morphological and/or molecular methods, we analyzed them by species complex as well as species. Onychomycosis caused by Fusarium spp. is predominantly found on the big toe, with Fusarium solani species complex and Fusarium oxysporum species complex accounting for over 70% of cases. Infection of only one digit with paronychia is a characteristic clinical manifestation of onychomycosis caused by Fusarium spp. Since there has been an increase in instances of molecular determination of Fusarium spp., it is deemed necessary to clarify its clinical and fungal nature. Due to its characteristic drug sensitivity and temperature-sensitive nature, new treatments are expected to be developed.