The most informative test is to scrape the lesion and add potassium hydroxide (KOH), then examine under a microscope. (KOH scrapings are commonly used to examine fungal infections.) The pathognomonic finding is observing Medlar bodies, sclerotic cells. Scrapings from the lesion can also be cultured to identify the organism involved. Blood tests and imaging studies are not commonly used.

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  SEM reveals some of the ultrastructural morphology this pigmented, or dematiaceous mould, Xylohypha nigrescens, know to cause phaeohyphomycosis, chromoblastomycosis, and mycetoma. From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph of the dematiaceous, or dark colored fungi Fonsecaea pedrosoi. From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph of the dematiaceous, or dark colored fungi Fonsecaea pedrosoi. From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph of Cladophialophora carrionii (475X mag). From Public Health Image Library (PHIL). ^[1]
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  Petri dish culture plate inoculated with a culture of the fungal organism, Exserohilum rostratum, extracted from a foot lesion of a phaeohyphomycosis patient. From Public Health Image Library (PHIL). ^[1]
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  Histopathologic changes associated with phaeohyphomycosis due to P. parasitica using methenamine silver stain. From Public Health Image Library (PHIL). ^[1]
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  Histopathologic changes associated with phaeohyphomycosis due to P. parasitica using H&E stain. From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph depicts conidia-laden conidiophores of a Phialophora verrucosa fungal organism from a slide culture. From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph depicts a conidia-laden conidiophore of a Phialophora verrucosa fungal organism from a slide culture. From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph prepared with gomori staining technique reveals histopathologic changes indicative of the presence of the dematiaceous fungal organism, Phialophora parasitica, a known causative agent for chromoblastomycosis (50x mag). From Public Health Image Library (PHIL). ^[1]
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  Gridley-stained photomicrograph reveals histopathologic changes, indicative of the chronic fungal disease process known as chromoblastomycosis, or chromomycosis. From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph reveals morphologic details displayed by the fungal organism, Phialophora parasitica, which is known to be a cause of chromoblastomycosis (1125x mag). From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph revealed some of the ultrastructural morphology exhibited by a cluster of Phialophora parasitica fungal conidia (1125x mag). From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph revealed some of the ultrastructural morphology displayed by the dematiaceous filamentous fungus, Phialophora richardsiae (1125x mag). From Public Health Image Library (PHIL). ^[1]
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  Photomicrograph revealed some of the ultrastructural morphology displayed by the dematiaceous filamentous fungus, Phialophora richardsiae (1125x mag). From Public Health Image Library (PHIL). ^[1]
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  Pathologic changes in a Brazilian patient’s right hand after having been infected by what was determined to be Phialophora verrucosa fungal organisms. From Public Health Image Library (PHIL). ^[1]
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  Histopathologic changes, which were indicative of the chronic fungal disease process known as chromoblastomycosis, or chromomycosis (1188x mag). From Public Health Image Library (PHIL). ^[1]