Onychomycosis, II: Diagnostic approach

Four main portals for fungi can be identified on the nail, each resulting i n different clinical patterns of infection: 1 - Via the distal subungual ar ea and the lateral nail groove leading to distal lateral subungual onychomy cosis. The fungus invades the horny layer of the hyponychium and/or the nai l bed, then the undersurface of the nail plate which becomes opaque. Endony x onychomycosis is a variant of this type. 2 - Via the dorsal surface of the nail prate, producing superficial onychom ycosis. Superficial white onychomycosis is normally confined to the toenail s. Superficial black onychomycosis, the counterpart of the latter, is very rare. 3 - Via the undersurface of the proximal nail fold which appears normal in proximal subungual onychomycosis. In patients with AIDS the term 'acute pro ximal nail dystrophy' might be appropriate for this type of infection. Prox imal leuconychia associated with paronychia is produced by non dermatophyte -moulds. 4 - Secondary total dystrophic onychomycosis represents the most advanced f orm of all the types described above. In contrast to this form, primary tot al dystrophic onychomycosis is observed only in patients suffering from chr onic mucocutaneous candidosis or in other immunodeficiency states. The diagnosis of onychomycosis always requires laboratory confirmation. Myc ological diagnosis is based on detection of fungal elements in direct micro scopy preparations and identification of the responsible fungus by culture. In repeated false negative mycological results, histopathological examinat ion of nail keratin may be helpful.