Mycetoma
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Direct answer
A painless subcutaneous swelling of the foot, present for months to years, that eventually breaks down into sinuses discharging grains — black, white, yellow or red — in a barefoot agricultural worker is mycetoma, a chronic granulomatous infection of skin, subcutaneous tissue and bone endemic to the "mycetoma belt" of Sudan, Senegal, Mexico and India (the Madurai-Tamil Nadu corridor and Rajasthan desert belt among the classic reports). The grain colour and microscopy split the two families: eumycetoma caused by fungi such as Madurella mycetomatis (black grains, thick-walled septate hyphae) treated with long itraconazole plus wide surgical excision, and actinomycetoma caused by filamentous bacteria such as Nocardia brasiliensis, Actinomadura and Streptomyces somaliensis (pale grains, thin filaments) treated with prolonged combined antibacterial therapy — cotrimoxazole with amikacin or rifampicin per current Mycetoma Research Centre protocols. Diagnosis is by grain examination, culture and matrix-assisted laser desorption ionisation or polymerase chain reaction where available, with radiography and magnetic resonance imaging mapping bone involvement.
What you must remember
- Triad definition: painless subcutaneous swelling, sinuses, and grains (sclerotia) in the discharge — the defining clinical triad, with the foot accounting for the majority of lesions ("Madura foot", named after Madurai in Tamil Nadu).
- Grain-to-organism map: black grains — Madurella mycetomatis and Trematosphaeria grisea (eumycetoma); white or yellow grains — Actinomadura madurae (white, large), Streptomyces somaliensis (yellow), Nocardia brasiliensis (white-pink, microabscess granules); red grains — Actinomadura pelletieri; the Indian viva loves this colour-key.
- Distinguishing features: eumycetoma — well-circumscribed lesions, slow growth, thick capsule, less bone destruction early; actinomycetoma — faster growth, more inflammatory, earlier bone invasion and more sinuses.
- Pathogenesis: traumatic inoculation of soil or thorn organisms into bare feet; thorn fragments embedded with grains are found histologically — occupation and footwear are the risk factors, and the male rural agricultural worker is the archetypal patient.
- Medical therapy: actinomycetoma — cotrimoxazole plus amikacin (the Welsh regime) or plus rifampicin, courses of many months; eumycetoma — itraconazole 200-400 mg daily for six months to a year or more; fosravuconazole has shown promise in trials. Surgery — wide local excision for localised eumycetoma, ray or below-knee amputation for advanced bone disease.
- Workup set: deep-needle or biopsy grain sampling with potassium hydroxide mount and histology, culture on Sabouraud agar, imaging with radiography (cavities, periosteal reaction) and magnetic resonance imaging (the "dot-in-circle" sign is characteristic), and serology where available.
- Programme recognition: mycetoma was added to the World Health Organization's list of neglected tropical diseases in 2016 — the first disease so added by a country's request (Sudan), an exam-worthy fact with the Mycetoma Research Centre in Khartoum anchoring global protocols.
Three confusions
Three confusions recur. First, mycetoma versus actinomycosis: the latter — Actinomyces israelii, a commensal of the mouth and gut — forms sinuses and yellow "sulphur" granules but is endogenous, cervicofacial or ileocaecal, and penicillin-responsive, whereas mycetoma is exogenous, traumatic, pedal and grain-colour-keyed. Second, eumycetoma versus actinomycetoma therapy is swapped: giving antifungals for actinomycetoma or antibiotics alone for eumycetoma wastes the disease's best chance at cure; the grain on potassium hydroxide is the pivot of the entire management plan. Third, chromoblastomycosis enters the differential — also traumatic implantation mycosis of bare limbs, but presenting as verrucous plaques with coppery sclerotic Medlar bodies on biopsy, not sinuses and grains, and the dot-in-circle sign on magnetic resonance imaging is the radiology one-liner worth remembering.
Frequently asked questions
What is the classical triad of mycetoma?
Painless subcutaneous swelling, multiple sinuses, and discharge containing grains — usually on the bare foot of an agricultural worker.
Which organism causes black-grain eumycetoma most commonly?
Madurella mycetomatis, seen as thick-walled septate hyphae within black grains.
How does treatment differ between eumycetoma and actinomycetoma?
Eumycetoma needs prolonged itraconazole with surgical excision; actinomycetoma responds to combined antibacterial therapy such as cotrimoxazole with amikacin or rifampicin.
What is the dot-in-circle sign?
A magnetic resonance imaging sign of tiny hyperintense foci within circular lesions, characteristic of mycetomatous granulomata.
Why is mycetoma called a neglected tropical disease?
It was added to the World Health Organization's neglected tropical disease list in 2016 after Sudan's request, reflecting its burden among the poorest barefoot farming populations.