[Unusual fungal species causing onychomycosis.]

Dermatomycoses caused by non-dermatophytic mycelial fungi are very rare with the exception of onychomycoses. Controversies regarding the pathogenic role often arise when these species and yeasts are isolated from nail scrapings. Candida albicans and Candida parapsilosis are the species identified more frequently from nails, particularly from finger nails. Because they could be resident flora of the skin, cultures should be interpreted according to clinical data, direct microscopic observation of clinical samples, and quantification of colonies. The recognition of other yeasts, such as Candida guillermondii, Candida famata or Candida krusei is more problematic. Isolation of moulds form toe nails accounts for 2 to 12% in different studies, with a prevalence of 7.6% in Barcelona being Scopulariopsis brevicaulis the most frequent species, but Aspergillus versicolor is also a particular etiologic agent of onychomycosis (2.5%). To confirm the etiology of any onychomycosis, standard criteria for mycological diagnosis and identification of moulds should be strictly applied. Experience in the diagnosis of superficial mycosis due to new species of fungi is required for improving current knowledge on the prevalence and clinical importance of this type of infections.