A mycotic infection of humans and animals caused by a number of different fungi and actinomycetes characterized by draining sinuses, granules and tumefaction. The disease results from the traumatic implantation of the aetiologic agent and usually involves the cutaneous and subcutaneous tissue, fascia and bone of the foot or hand. Sinuses discharge serosanguinous fluid containing the granules which vary in size, colour and degree of hardness, depending on the aetiologic species, and are the hallmark of mycetoma. World-wide distribution but most common in bare-footed populations living in tropical or subtropical regions. Aetiological agents include Madurella, Acremonium, Pseudallescheria, Exophiala, Leptosphaeria, Curvularia, Fusarium, Aspergillus etc.
Mycetoma is a chronic, suppurative infection of the subcutaneous tissue and contiguous bone. The clinical features are fairly uniform, regardless of the organism involved. The feet are the most coomon site for infection and account for at least two-thirds of cases. Other sites include the lower legs, hands, head, neck, chest, shoulder and arms. Most cases start out as a small hard painless nodule which over time begins to soften on the surface and ulcerate to discharge a viscous, purulent fluid containing grains. The infection slowly spreads to adjacent tissue, including bone, often causing considerable deformity. Sinuses continue to discharge serosanguinous fluid containing the granules which vary in size, colour and degree of hardness, depending on the aetiologic species. These grains are the hallmark of mycetoma.
Mycetoma showing numerous draining sinuses. There is destruction of bone, distortion of the foot, and hyperplasia at the openings of the sinus tracts. (Courtesy John Rippon USA).
Excised mycetoma showing a draining sinus (cut open in this preparation) containing black grains.
1. Clinical Material: Tissue biopsy or excised sinus, serosanguinous fluid containing the granules which vary in size, colour and degree of hardness, depending on the aetiologic species.
2. Direct Microscopy: Serosanguinous fluid containing the granules should be examined using either 10% KOH and Parker ink or calcofluor white mounts, and tissue sections should be stained using H&E, PAS digest, and Grocott's methenamine silver (GMS).
H&E stained tissue section showing blacked grained eumycotic mycetoma caused by Madurella mycetomatis.
Interpretation: The presence of white to yellow or black pigmented grains, from a patient with supporting clinical symptoms should be considered significant. Biopsy and evidence of tissue invasion is of particular importance. Remember direct microscopy or histopathology does not offer a specific identification of the causative agent.
3. Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar.
4. Serology: There are currently no commercially available serological procedures for the diagnosis of mycetoma.
5. Identification: Characteristic clinical, microscopic and culture features.
Acremonium sp., Aspergillus nidulans, Madurella grisea, Madurella mycetomatis, Scedosporium apiospermum.
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Richardson MD and DW Warnock. 1993. Fungal Infection: Diagnosis and Management. Blackwell Scientific Publications, London.
Rippon JW. 1988. Medical Mycology WB Saunders Co.