Onychomycosis: classification and diagnosis.

Onychomycosis is a common infection of the nail predominantly caused by anthropophilic dermatophytes, and to a lesser extent by yeasts (Candida species) and non-dermatophyte molds. The treatment of onychomycosis is dependent on several variables, including the type of onychomycosis and the causative organism. Various techniques have been used to accurately diagnose onychomycosis, with microscopy and culture being used most frequently. Histological examination of the distal nail plate can aid in confirming the presence of invasive nail disease, but histological examination should not be limited to the nail plate as it may also be helpful in diagnosing subungual onychomycosis. Nucleic acid-based identification techniques may also be valuable when diagnosing onychomycosis; however, multiple steps may be necessary to determine the causative species. Confocal microscopy may also be a fast and reliable method of diagnosing onychomycosis, though it has very limited ability to distinguish between dermatophyte and mold infections. Prior to treatment an accurate diagnosis can provide guidance about the choice of antifungal agent, especially since the causative organism may vary in its response to the antifungal therapies available.