Onychomycosis Classification


The first classification of onychomycosis was proposed by Zaias, and is based on the clinical
appearance of the nails (Zaias, 1972). He described four clinical types: [1] distal subungual
onychomycosis (DSO), [2] white superficial onychomycosis (WSO), [3] proximal subungual
onychomycosis (PSO) and [4] Candida sp. onychomycosis. Since the publication of this
paper, some modifications have been added. In 1998, Baran et al. proposed [I] distal and
lateral subungual onychomycosis (DLSO), [II] superficial onychomycosis, [III] proximal
subungual onychomycosis (PSO), [IV] endonyx onychomycosis and [V] total dystrophic
onychomycosis (TDO). The most used these days is the following: DLSO, white superficial
onychomycosis (WSO), PSO, Candida onychomycosis (paronychia) and TDO (Table 1) ,
(Baran et al 1998). WSO and PSO are also known as mycotic leukonychia. Further
subdivisions are included in almost all the categories, and will be discussed further when
necessary (Gupta & Summerbell, 1999).
In 1976, English described a classification based on etiology, instead of the clinical aspect of
the fungal invasion. The categories are: (a) dermatophytes causing tinea unguium, (b) moulds
(Non-dermatophyte moulds [NDM]) and (c) yeasts (Crozier et al. 1979). At this moment, the
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Distal and lateral subungual onychomycosis (DLSO)
Proximal white subungual onychomycosis (PWSO)
Superficial white onychomycosis (SWO)
Total dystrophic onychomycosis (TDO)
Candida paronychia
Table 1. Current clinical classification

current classifications are not being specific enough to describe the clinical picture, etiology
or prognostic factors regarding response to treatment (Grossman & Scher, 1990). Fungal or
mycotic leukonychia was rather infrequent until the AIDS pandemia. PWSO is the least
common form of onychomycosis in the HIV negative population, and DLSO is the most
prevalent form of onychomycosis in patients living with HIV/AIDS. Since the identification
of this disease in the 1980´s, many case reports and studies have been done. Although
onychomycosis is not considered an AIDS-defining illness, and its presence is not useful for
clinical classification, the presence of fungal leukonychia should alert the physician about
possible immunosuppression. However, PSWO heralds advanced HIV disease and can be
an early clinical marker of HIV infection (Chang & Arenas, 1995).
For some patients and even some physicians, onychomycosis

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