Onychomycosis, the Active Invasion of a Normal Nail Unit by a Dermatophytic Versus the Colonization of an Existing Abnormal Nail Unit by Environmental Fungus.

Onychomycosis was described by early investigators as the presence of an abnormal nail unit and a member of the order Mycota, producing the abnormality. This interpretation has caused more than 50 years of confusion in the dermatologic literature. Unquestionably, the clinician sees more abnormal toenails than fingernails, and investigators have described a multitude of fungi as the cause of the clinically abnormal toenail. In 2010, developmental scientists proved, what we have long recognized, that there is no bilateral symmetry in living organisms and, therefore, one sole is different from the other. This causes a gait asymmetry, coupled with the pressure the closed shoe exerts on toenails while walking. This produces a series of abnormalities, which are clinically identical to what has been described for dermatophytic onychomycosis. These are fungus free and result in toenail niches. These toenail abnormalities were recently described as the asymmetric gait nail unit syndrome (AGNUS). It is possible that environmental fungi can colonize these toenail niches and, therefore, were described by investigators as a new onychomycosis entity In the normal host, onychomycosis should be only used to describe the active invasion of the nail bed (NB) corneocytes by a dermatophyte, as seen in dermatophytic onychomycosis. Dermatophytes only affect those hosts who have inherited the dermatophytosis susceptibility gene, transmitted as an autosomal dominant trait. In studies encompassing 3,000 abnormal toenails, only 27%-30% were found as dermatophyte culture positive, 25% were negative and the rest environmental fungi were recovered.