Review
Fungal melanonychia

https://doi.org/10.1016/j.jaad.2010.11.018Get rights and content

Fungal melanonychia is a relatively rare nail disorder caused by nail infection that produces brown-to-black pigmentation of the nail unit. The number of organisms implicated as etiologic agents of fungal melanonychia is increasing, and the list currently tops 21 species of dematiaceous fungi and at least 8 species of nondematiaceous fungi. These superficial infections may clinically mimic subungual melanoma and are often not responsive to traditional antifungal therapy. This article reviews the literature on fungal melanonychia and the role of fungal melanin in infection.

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

References (97)

  • A. Tosti et al.

    Nail matrix nevi: a clinical and histopathological study of twenty-two patients

    J Am Acad Dermatol

    (1996)
  • J.E. Arrese et al.

    Fungi in onychomycosis: a study by immunohistochemistry and dual flow cytometry

    J Eur Acad Dermatol Venereol

    (1995)
  • P.R. De Doncker et al.

    Itraconazole therapy is effective for pedal onychomycosis caused by some nondermatophyte molds and in mixed infection with dermatophytes and molds: a multicenter study with 36 patients

    J Am Acad Dermatol

    (1997)
  • R.C. Pritchard et al.

    Black fungi: a survey of dematiaceous hyphomycetes from clinical specimens identified over a five year period in a reference laboratory

    Pathology

    (1987)
  • R. Baran et al.

    Longitudinal melanonychia (melanonychia striata): diagnosis and management

    J Am Acad Dermatol

    (1989)
  • E. Punithalingam et al.

    Pyrenochaeta unguis-hominis sp.nov. on human toenails

    Transactions of the British Mycological Society

    (1975)
  • G. Badillet

    Mélanonychies superficielles

    Bulletin de la Societe Française de Mycologie Medicale

    (1988)
  • M.E. Brandt et al.

    Epidemiology, clinical manifestations, and therapy of infections caused by dematiaceous fungi

    J Chemother

    (2003)
  • R.J. Hay et al.

    Clinical features of superficial fungal infections caused by Hendersonula toruloidea and Scytalidium hyalinum

    Br J Dermatol

    (1984)
  • N.L. Sharma et al.

    Subcutaneous pheohyphomycosis in India–a case report and review

    Int J Dermatol

    (2002)
  • R. Kotrajaras et al.

    Hendersonula toruloidea infection in Thailand

    Int J Dermatol

    (1988)
  • A.R. Costa et al.

    Cutaneous and ungual phaeohyphomycosis caused by species of Chaetomium Kunze (1817) ex Fresenius, 1829

    J Med Vet Mycol

    (1988)
  • M.G. Little et al.

    Scytalidium dimidiatum in Australia

    Australas J Dermatol

    (1995)
  • J.E. Arrese et al.

    Onychomycosis and keratomycosis caused by Alternaria sp.: a bipolar opportunistic infection in a wood-pulp worker on chronic steroid therapy

    Am J Dermatol

    (1996)
  • S.M. Singh et al.

    Ungual and cutaneous phaeohyphomycosis caused by Alternaria alternata and Alternaria chlamydospora

    J Med Vet Mycol

    (1990)
  • C. Romano et al.

    Onychomycosis caused by Alternaria spp. in Tuscany, Italy from 1985 to 1999

    Mycoses

    (2001)
  • K. Wadhwani et al.

    Some cases of onychomycosis from North India in different working environments

    Mycopathologica

    (1985)
  • C. Romano et al.

    Retrospective study of onychomycosis in Italy: 1985-2000

    Mycoses

    (2005)
  • M.K. Moore

    Hendersonula toruloidea and Scytalidium hyalinum infections in London, England

    J Med Vet Mycol

    (1986)
  • M. Kombila et al.

    Hendersonula toruloidea as an agent of mycotic foot infection in Gabon

    J Med Vet Mycol

    (1990)
  • V.Y. Allison et al.

    Hendersonula toruloidea and Scytalidium hyalinum infections in Tobago

    Br J Dermatol

    (1984)
  • M.K. Moore

    Skin and nail infections by nondermatophyte filamentous fungi

    Mykosen Suppl

    (1978)
  • T. Matsumoto et al.

    Fungal melanonychia: ungual phaeohyphomycosis caused by Wangiella dermatitidis

    Clin Exp Dermatol

    (1992)
  • R. Baran et al.

    Uncommon clinical patterns of Fusarium nail infection: report of three cases

    Br J Dermatol

    (1997)
  • J.R. Vierira

    Onychomycose por Aureobasidium pullulans (De Bary) Arnaud

    Proceedings of the Congress for Tropical Medicine and Malaria

    (1961)
  • O. Male et al.

    Nagelveranderungen durch Schimmelpilze

    Dermatologische Wochenschrift

    (1965)
  • L. Gip et al.

    Onychomycosis caused by Phyllostictina sydow

    Acta Derm Venereol

    (1967)
  • G. Badillet et al.

    Etude retrospective des Trichophyton rubrum á pigment noir diffusible isolés á Paris de 1971 á 1980

    Bulletin de la Societe Française de Mycologie Medicale

    (1984)
  • M. Baxter

    The stimulation of pigment production by Trichophyton rubrum on a new medium

    Sabouraudia

    (1963)
  • A.C. Ray et al.

    Studies on the biosynthesis of aspergillin by Aspergillus niger

    Appl Microbiol

    (1975)
  • J.J. Finch et al.

    Toenail onychomycosis: current and future treatment options

    Dermatol Ther

    (2007)
  • A.H. Parlak et al.

    A case of melanonychia due to Candida albicans

    Clin Dermatol

    (2006)
  • A. Velez

    Melanonychia due to Candida humicola

    Br J Dermatol

    (1996)
  • P. Gautret et al.

    Case report and review: onychomycosis due to Candida parapsilosis

    Mycoses

    (2000)
  • S.W. Lee et al.

    Fungal melanonychia

    J Dermatol

    (2004)
  • R. Morris-Jones et al.

    Synthesis of melanin pigment by Candida albicans in vitro and during infection

    Infect Immun

    (2005)
  • K.E. Lyke et al.

    A case of cutaneous ulcerative alternariosis: rare association with diabetes mellitus and unusual failure of itraconazole treatment

    Clin Infect Dis

    (2001)
  • B.E. Taylor et al.

    Evidence for pentaketide melanin biosynthesis in dematiaceous human pathogenic fungi

    Mycologia

    (1987)
  • Cited by (0)

    Funding sources: None.

    Conflicts of interest: None declared.

    View full text