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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z



Mycetoma

Mycetoma is a chronic infection of the skin, subcutaneous tissue and sometimes bone characterised by discharging sinuses filled with organisms. It is generally found on the foot where it is given the name watering can foot.

Mycetoma may be due to several fungi (when it is called eumycetoma) or actinomycetes (actinomycetoma). Actinomycetes are bacteria that produce filaments, like fungi. Both the fungi and the actinomycetes are found in soil and plant material in tropical regions.

The organism is inoculated into the skin by a minor injury, for example, a cut with a thorn when barefoot. It is not endemic in New Zealand but mycetoma is occasionally diagnosed in native Pacific Islanders.

Mycetoma
Long standing mycetoma
Mycetoma
Sinuses from Nocardia

The most common fungi to cause mycetoma with black grains are:

The most common fungi to cause mycetoma with white grains are:

The most common actinomycetes to cause mycetoma with white/yellow grains are:

Brown or red grains occur in mycetoma due to:

Clinical features of mycetoma

Mycetoma is more common in men than women, particularly those aged 20 to 50. It generally presents as a single lesion on an exposed site and may persist for years. Two thirds arise on the foot.

The infection is occasionally confused with other skin conditions such as:

Diagnosis of mycetoma

The diagnosis of mycetoma depends on identifying grains. These are obtained using a needle and syringe to extract material from a soft part of the lesion under the skin or by collecting pus. Occasionally a skin biopsy is necessary, which shows characteristic histopathological features of mycetoma and may reveal the organisms.

Laboratory tests

The colour of the grains may suggest the likely diagnosis; black grains suggest a fungal infection, minute white grains suggest nocardia and red grains are due to Actinomadura pelletieri. Larger white grains or yellow-white grains may be fungal or actinomycotic in origin.

Microscopy using potassium hydroxide (KOH) confirms the diagnosis and type of mycetoma.

Several agar plates are cultured at 25-30 degrees celcius and 37 degrees celcius for up to six weeks. Fungi grow more quickly than actinomycetes.

Treatment of mycetoma

Mycetoma does not resolve without active treatment.

Actinomycetoma responds well to treatment with appropriate antibiotics but they are required for months or years. The sinuses dry up, swelling and tenderness improves and the grains disappear. Deformity may persist.

Single or combination treatment is used:

Eumycetoma is more difficult to treat.

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