First Report of Nothophoma quercina as a Novel Pathogen in Onychomycosis

Onychomycosis is a prevalent fungal infection of the nail apparatus, predominantly caused by dermatophytes. However, nondermatophytic molds, while less common, represent an increasingly recognized etiological group. Among these, Aspergillus, Scopulariopsis, Neoscytalidium, and Fusarium species are frequently implicated. Advancements in molecular diagnostic techniques have facilitated the identification of rare and emerging fungal pathogens implicated in onychomycosis. This case report details the first recorded case of onychomycosis caused by Nothophoma quercina, a fungal species that was previously recognized only as a plant pathogen. A 44-year- old male with severe atopic dermatitis receiving long-term immunosuppressive therapy with cyclosporine and dupilumab developed persistent nail abnormalities. Mycological evaluation, which included potassium hydroxide testing, fungal culture, and molecular analysis, confirmed Nothophoma quercina as the causal organism. The presence of this rare fungus in a human infection underscores the expanding spectrum of nondermatophytic onychomycosis and emphasizes the need to consider atypical pathogens in immunocompromised individuals. The growing use of molecular techniques has facilitated the detection of novel fungal species that may have been previously misidentified or disregarded using conventional methods. This case highlights the need for clinicians to exercise caution while assessing refractory onychomycosis, particularly in high-risk patients. Greater awareness and continued research into rare fungal pathogens will enhance the diagnostic accuracy and developing appropriate antifungal management strategies.