This is a chronic granulomatous disease commonly affecting the foot with extensive granulation tissue formation and bone destruction. The disease is common in the tropics and occurs through a prick in barefoot walkers in 90% of cases. The causative microorganisms for this infection are various fungi or actinomycetes found in road dust.
Several fungi can cause eumycetoma, including: Madurella mycetomatis, Madurella grisea, Leptosphaeria senegalensis, Curvularia lunata,Scedosporium apiospermum, Neotestudina rosatii, Acremonium spp. and Fusarium spp.. Diagnosis is by visualising the fungi under the microscope, biopsy, and culture.
Signs and symptoms
The initial lesion is a small swelling under the skin following minor trauma. It appears as a painless wet nodule, which may be present for years before ulceration, swelling and weeping from sinuses, followed by bone deformity. The sinuses discharge a grainy liquid of fungal colonies. These grains are usually black or white. Destruction of deeper tissues, and deformity and loss of function in the affected limbs may occur in later stages. It tends to occur in one foot. Mycetoma due to bacteria has similar clinical features.
- Firm, painless, pale nodule appears initially followed by others
- Vesicles surrounding the nodules which later burst and form sinuses
- Watery discharge, which may contain granules appearing yellow, red or black color
- Flattening of the convexity of inner foot
- Deep spread to bones subcutaneous plane leading to secondary infection.
Diagnosis is by visualising the fungi under the microscope, biopsy, and culture, which show characteristic fungal filaments and vesicles characteristic of the fungi. Molecular techniques may help to identify the infecting fungus
X rays and ultrasonography may be carried out to assess the extent of the disease. X rays findings are extremely variable. The disease is most often observed at an advanced stage that exhibits extensive destruction of all bones of the foot. Rarely, a single lesion may be seen in the tibia where the picture is identical with chronic osteomyelitis. Cytology of fine needle aspirate or pus from the lesion, and tissue biopsy may be undertaken sometimes. Some publications have claimed a “dot in a circle sign” as a characteristic MRI feature for this condition (this feature has also been described on ultrasound).
The following clinical conditions may be considered before diagnosing a patient with mycetoma:
- Tuberculous ulcer
- Kaposi’s sarcoma, a vascular tumour of skin usually seen in AIDS.
- Malignant neoplasm
- Tropical ulcer
- Botryomycosis, a skin infection usually caused by the bacteria Staphylococcus aureus.
- Sulphonamides and Dapson (prolonged course)
- Broad spectrum antibiotics for secondary infection
- Amputation if severe and disfiguring infection