[Nail histomycology. Protean aspects of a human fungal bed].

Onychomycosis exhibits considerable diversity when the disease is scrutinized using traditional, fluorescence or confocal microscopy. Histomycology is a non-invasive assessment performed on nail clippings. The location of and the density in fungal cells is variable. In some instances, these aspects remain clinically unsuspected. In vivo confocal microscopy can provide the same information. Computerized image analysis of histological sections is the most powerful means for quantifying the fungal load. Immunohistochemistry provides information about the identity of the fungus or the association of different fungi present in the nail plate. Mixed infections may be unifocal or located at different levels in the nail apparatus. The viability of fungi as assessed by vital stains can be visualized under the microscope and quantified by flow cytometry. The different aspects of nail histomycology are complementary and shed some light on sometimes unsuspected aspects of onychomycoses.