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Pathology of Pigmented (Dematiaceous) Fungi - Chromomycosis and Phaeohypomycosis

Dr Sampurna Roy MD

 

 

Pathology of Chromoblastomycosis - [Infographic]

                                                                                                                      

 

 

6 Important features of Dematiaceous Fungi:

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.

 

Pathology of 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. 

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 (Lupus Vulgaris) .  

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.

Pathology of Phaeohyphomycosis

 

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: 

i)  Superficial
ii) Cutaneous and corneal
iii) Subcutaneous
iv) Visceral

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. 

Image Link (Chromomycosis and Phaeohyphomycosis)- Dr Yutaka Tsutumi MD

 

Further reading:

Chromoblastomycosis and phaeohyphomycosis: new concepts, diagnosis, and mycology.

Chromomycosis caused by Exophiala spinifera.

Subcutaneous phaeohyphomycosis due to Exophiala spinifera in a renal transplant recipient.

An unusual dematiaceous fungal infection of the skin caused by Fonsecaea pedrosoi: a case report and review of the literature.  

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

 

 

 

Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)


 

 

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