Pathology of Pigmented (Dematiaceous) Fungi - Chromomycosis and Phaeohypomycosis
|6 Important features of
1) Fungal infection caused by dematiaceous fungi has been described worldwide, although the incidence is higher in countries with tropical and subtropical climate.
2) The fungal organisms are usually found in the soil and decaying vegetable matter.
3) These fungi have darkly pigmented hyphae, spores or both.
4) The brown pigment in the fungi is a melanin which can be clearly demonstrated in tissue section by the stains for melanin.
5) Infection usually occurs due traumatic inoculation of the organism into the skin.
6) They cause primarily two groups of infections- Chromomycosis and Phaeohyphomycosis.
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.
Clinically, the lesion starts as a scaly papule which later grows into warty nodule or plaque at the site of implantation.
Microscopically the skin shows hyperkeratosis and pseudoepitheliomatous hyperplasia and a diffuse chronic inflammatory infiltrate.
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.
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, Exophiala spinifera, Wangiella dermatitidis.
The four main clincal variants:
The cutaneous lesions usually present as solitary cystic, nodular or verrucous growths.
Histologically, there is a circumscribed cystic space or abscess in the lower dermis or subcutis.
Histopathologic changes in phaeohyphomycosis due to Wangiella dermatitidis using PAS stain. (CDC/Dr. Libero Ajello)
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.
due to Exophiala spinifera in a renal transplant recipient.
Chromoblastomycosis and phaeohyphomycosis. Semin Dermatol 1985;4: 240-251
Phaeohyphomycosis; definition and etiology. In Mycoses. Pan American Health Organization Scientific Publication No. 304. Washington DC; 1975; 126-130
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