ReviewFungal melanonychia
Section snippets
Etiology
Although the vast majority of onychomycosis is a result of dermatophytes, the incidence of onychomycosis caused by nondermatophytic molds such as dematiaceous fungi is increasing. Nondermatophytic molds account for 1.5% to 17.5% of onychomycosis.1, 2 The number of organisms implicated as etiologic agents of fungal melanonychia is increasing, and the list currently tops 21 species of dematiaceous fungi (Table I) and at least 8 species of nondematiaceous fungi (Table II). The dematiaceous fungi
Epidemiology
The geographic distribution of the etiologic agents of phaeohyphomycosis is widespread, increasing with proximity to the equator. As with dermatophyte onychomycosis, the prevalence of fungal melanonychia increases with age, has a higher incidence in men than in women, and more frequently involves toenails than fingernails. However, although infections as a result of dermatophytes are contagious, infections caused by dematiaceous fungi have not been shown to be contagious.3
Given our knowledge of
The role of fungal melanin in infection
There is growing evidence that melanin may play an important role in the pathogenesis of fungal melanonychia. Melanins are high molecular–weight brown-to-black pigments that are found in human beings, plants, and fungi alike, although their molecular structure and synthesis vary. Fungal melanins are synthesized in the cytoplasm and subsequently excreted as extracellular polymers or deposited in the cell wall. In most dematiaceous fungi, melanin is incorporated into the cell wall.
Unlike
Clinical presentation
The nail in fungal melanonychia is typically brown to black in color, sometimes dystrophic, and may be raised as a result of subungual hyperkeratosis (Fig 2). Periungual inflammation is common. The clinical pattern of nail involvement can raise clues as to the origin of infection. For example, longitudinal melanonychia is more common with strains of dermatophyte such as T rubrum varietas nigricans that produce a soluble, nongranular pigment that impregnates the nail bed, staining it brown to
Differential diagnosis
Several noninfectious conditions can cause brown-to-black pigmentation of the nail that may resemble fungal melanonychia and are worthy of mention. A detailed patient history is an important part of the clinical examination of a pigmented nail. Occupational exposures, athletic activities, medications, and changes in the nail over time can contribute to the differential diagnosis of the pigmentation. For a detailed summary of the differential diagnosis of nail pigmentations, refer to the recent
Diagnosis
With the ever-lengthening list of causative agents of fungal melanonychia and their resistance to most antifungal therapy, it is important to accurately identify the causative organism to aid in appropriate treatment. Direct microscopic examination (eg, with potassium hydroxide or chlorazol black E) is essential to confirm infection by ascertaining the presence of fungal hyphae/filaments or yeast pseudohyphae. With dematiaceous organisms, the pigmentation is often clearly seen in direct
Treatment
Ungual phaeohyphomycosis is notoriously difficult to treat. Given the low incidence of fungal melanonychia, most of the knowledge of treatment efficacy has been derived from case reports or small open clinical trials. It is unlikely that large prospective randomized trials will be conducted. There have been many in vitro studies of antifungal therapy directed at a wide range of dematiaceous molds, but because of variability in nail penetration and drug metabolism, results of in vitro studies do
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