Atypical fingernail onychomycosis due to Aspergillus niger in a healthy adult: an unusual presentation of a non-dermatophyte mold infection.

BACKGROUND: Onychomycosis is commonly caused by dermatophytes, but nondermatophytic molds (NDMs) are increasingly recognized, even in immunocompetent individuals. These infections often present atypically, leading to delayed diagnosis. NDMs require accurate identification, as they may not respond to standard antifungal treatments used for dermatophyte infections. CASE REPORT: An immunocompetent man in his 40s presented with discoloration of a single right index fingernail. He reported no trauma, systemic illness, or immunosuppressive therapy. Examination revealed brown-black nail discoloration with a milky-white base and mild nail dystrophy, without onycholysis or subungual debris. Other nails were unaffected. A provisional diagnosis of nondermatophytic mold onychomycosis was made. Nail clippings were sent for fungal culture showing growth of Aspergillus niger. CONCLUSION: NDM onychomycosis should be considered in isolated nail discoloration, even in healthy individuals. Early laboratory evaluation is crucial for accurate diagnosis and effective, targeted antifungal therapy. CLINICAL TRIAL: Not applicable.