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Characteristic
features of dematiaceous fungi:
- Fungal infection caused by dematiaceous fungi has been described
worldwide, although the incidence is higher in countries with tropical and
subtropical climate.
- The fungal organisms are usually found in the soil and decaying
vegetable matter.
- These fungi have darkly pigmented hyphae, spores or both.
- The brown pigment in the fungi is a melanin which can be clearly
demonstrated in tissue section by the stains for melanin.
- Infection usually occurs due traumatic inoculation of the organism into
the skin.
- They cause primarily two groups of infections- Chromomycosis and
phaeohyphomycosis.
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Chromomycosis/Chromoblastomycosis |
Chromomycosis is a
chronic slowly progressive and localised lesion of the skin and
subcutaneous tissue caused by traumatic implantation of dematiaceous fungi
into the skin. The lesion may also occur in immunocompromised patients.
The organisms that are known to cause chromoblastomycosis include
Fonsecaea pedrosoi, Fonsecaea compacta, Phialophora verrucosa and
Cladosporium carrionii.
The lesions are usually localized to the distal part of the extremities.
Rarely these are located on the hands, arms and the
buttocks.
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Clinically, the lesion starts as a scaly papule which later grows into
warty nodule or plaque at the site of implantation. Grossly the verrucous
plaque in chromomycosis may resemble sporotrichosis, cutaneous
leishmaniasis and cutaneous tuberculosis.
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Microscopically the skin shows hyperkeratosis and pseudoepitheliomatous
hyperplasia and a diffuse chronic inflammatory infiltrate.
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The organisms are round, golden brown in colour and thick walled. These
are known as sclerotic bodies,muriform cells or medlar bodies and are 5-12
micrometer in diameter. The muriform fungal cells are usually located
within the giant cells or lie within microabscesses.The organisms are
easily identified in hematoxylin and eosin stained sections.
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Most of the granulomas identified are tuberculoid in type, together with
a few suppurative granulomas. These are usually present in the upper and
mid dermis. Intraepidermal microabscesses are also identified. In
sporotrichosis microabscesses are more prominent.
There is transepithelial elimination of fungal bodies and inflammatory
debris.
Dermal fibrosis is prominent in treated cases.
It has been reported that very rarely malignant transformation may occur
in longstanding cases chromoblastomycosis.
Phaeohyphomycosis is
a collective term for a heterogeneous group of fungal infections caused by
dematiaceous fungi.
The infection is often seen following traumatic implantation of an
infected splinter or other vegetable matter.
The commonly isolated fungi include Exophiala jeanselmei, E. spinifera,
Wangiella dermatitidis.
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The four main
clincal variants:
i) Superficial
ii) Cutaneous and corneal
iii) Subcutaneous
iv) Visceral
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The cutaneous lesions usually present as solitary cystic, nodular or
verrucous growths.
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Link (Dr Tsutsumi MD)
Histologically there is a circumscribed cystic space or abscess in the
lower dermis or subcutis. A wood splinter may be present within the
cyst. There is a granulomation tissue reaction in the surrounding stroma.
The cyst wall contains chronic inflammatory cells together with some giant
cells. The fungal hyphae are brown and filamentous. These are present
within the giant cells or along the cyst wall or within inflammatory
debris.
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