Objective: To analyze the epidemiology, responsible agents, clinical features, and outcome of white superficial onychomycosis (WSO). Design: Retrospective study. Setting: University hospital. Patients: A total of 79 patients with WSO seen at the Department of Dermatology of Bologna University from 1994 to 2002. Responsible agents included Trichophyton interdigitale in 58 cases (73%), Trichophyton rubrum in 4 (5%), Fusarium species in 9 (11%), Aspergillus species in 5 (6%), and Acremonium strictum in 3 (3%). Results: White superficial onychomycosis may have different clinical and epidemiological features. "Classic" WSO, characterized by superficial nail plate involvement, is usually due to Trichophyton mentagrophytes (var interdigitale), although Acremonium strictum or Onychocola canadiensis can sometimes be responsible. A deep and diffuse WSO, characterized by massive penetration of the nail plate by fungi, can be seen in nail infections by molds such as Fusarium species and Aspergillus species, or in nail infections by Trichophyton rubrum in healthy children and in patients infected with human immunodeficiency virus. Conclusions: Severity and spread of WSO is the result of complex host-parasite relationships. When dealing with a patient with WSO, we should always consider the causative organism and the host characteristics to choose the best therapeutic approach.
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