Conditions · Infectious and tropical diseases
Mycetoma (actinomycetoma and eumycetoma) !
Mycetoma is a slow, painless infection under the skin, usually of the foot, that forms draining sinuses with grains and can destroy bone.
Updated 2026-11-01
Structures involved
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- Skin
- First metatarsal
- Fifth metatarsal
- Calcaneus
- Second metatarsal
- Third metatarsal
- Fourth metatarsal
- Talus
- Navicular
- Cuboid
- Medial cuneiform
- Plantar fascia
- Tibia
Microorganisms that cause it
Why it happens
- Granulomatous inflammation: caseating vs non-caseating, the causes to know
- Fibrosis in organs: TGF-β and the myofibroblast
- Bone tissue: cells, compact and spongy bone
What it is
A chronic, progressive granulomatous infection of the skin, subcutaneous tissue and later muscle and bone, caused by soil bacteria (actinomycetoma) or fungi (eumycetoma) that enter through minor wounds. Its classic triad is a painless swelling, multiple draining sinuses and discharge of grains.
Who gets it
It occurs in the tropical and subtropical "mycetoma belt", with Mexico and Sudan reporting most cases. In Latin America most cases are actinomycetoma, mainly from Nocardia species; in Colombia it is uncommon, with small case series from rural, warm areas. It mainly affects young adult men who work barefoot in agriculture. It is not contagious and is not a notifiable disease, so its true burden is unknown.
Causes
- Actinomycetoma: aerobic filamentous bacteria such as Nocardia (N. brasiliensis is the leading cause in Latin America), Actinomadura and Streptomyces
- Eumycetoma: true fungi such as Madurella mycetomatis, the leading cause in Africa
- Inoculation from soil or plant material through thorn pricks, splinters or small injuries
Risk factors
- Walking barefoot or in open footwear
- Farm work, herding and other manual outdoor labour
- Living in rural tropical areas with dry seasons and thorny vegetation
- Poverty and limited access to health services, which delay diagnosis
Pathophysiology
After inoculation the organisms form compact colonies (grains) surrounded by neutrophils, then granulomas and fibrosis. The infection spreads slowly along fascial planes to muscle and bone, forming abscesses that open to the skin as sinuses discharging pus with grains. Bone is invaded and destroyed, with periosteal reaction and lytic cavities. Pain is usually mild until secondary bacterial infection or bone involvement.
Classification
- Actinomycetoma (bacterial): usually faster and more inflammatory, with earlier bone involvement; responds to antibiotics
- Eumycetoma (fungal): slower and more encapsulated; needs antifungals plus surgery
- By grain colour: black grains point to a fungus and red grains to bacteria; white or yellow grains can be either
Symptoms and signs
- Slowly growing, firm, painless swelling of the foot (less often the hand, leg, back or head)
- Multiple nodules and sinuses that drain pus containing visible grains
- Scarring, deformity and swelling of the whole foot over months to years
- Pain when there is secondary infection or bone destruction
- Loss of function and difficulty walking in advanced disease
Diagnosis
- Clinical
- Suspected in a person from a rural tropical area with a chronic, painless swelling of the foot that has draining sinuses. Identifying the grains and their colour points to the cause.
- Tests
- Grains obtained by fine-needle aspiration, from the discharge or by deep surgical biopsy, examined directly (including Gram stain and potassium hydroxide), by histology and culture; PCR is the most accurate but is not widely available. Distinguishing bacterial from fungal disease is essential because treatment differs completely.
- Imaging
- Plain X-ray for periosteal reaction, bone cavities and destruction; ultrasound (grains appear as bright echoes in cavities) and MRI (the "dot-in-circle" sign) to map the extent before surgery.
Differential diagnosis
- Chronic bacterial osteomyelitis
- Chromoblastomycosis and sporotrichosis
- Botryomycosis (bacterial grains, usually Staphylococcus)
- Tuberculosis of skin or bone
- Soft-tissue tumours such as Kaposi sarcoma
Goal of treatment
Identify whether the cause is bacterial or fungal, give long targeted treatment, remove the infected tissue when needed and preserve the limb and its function.
Treatment
- Medical
- Actinomycetoma: prolonged combination antibiotics, typically trimethoprim-sulfamethoxazole, with an aminoglycoside such as amikacin added in extensive or deep disease.
- Medical
- Eumycetoma: long courses of azole antifungals (for example itraconazole), usually combined with surgery.
- Surgical
- Wide excision of localised lesions, mainly in eumycetoma; amputation is reserved for extensive bone destruction, uncontrolled infection or failure of medical treatment.
- Follow-up
- Follow-up for months to years for drug adverse effects (kidney function and hearing with aminoglycosides, liver tests with azoles), healing of sinuses and recurrence.
Complications
- Bone destruction, deformity and disability
- Secondary bacterial infection and sepsis
- Recurrence after surgery, especially in eumycetoma
- Amputation
- Spread to spine, lungs or brain from lesions of the back or head
Prognosis
Actinomycetoma often responds to antibiotics if treated early. Eumycetoma has lower cure rates, frequent relapse and more amputations. Late presentation, common in poor rural areas, worsens outcomes.
Prevention
- Wearing shoes and protective clothing during field work
- Prompt cleaning of thorn pricks and small wounds
- Early recognition of chronic foot swellings in endemic areas
Test yourself
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What is the classic triad of mycetoma?
A painless subcutaneous swelling, multiple draining sinuses and discharge of grains.
What is the main cause of mycetoma in Latin America?
Actinomycetoma, mainly due to Nocardia brasiliensis.
Why must actinomycetoma and eumycetoma be distinguished?
Actinomycetoma is treated with antibiotics, whereas eumycetoma needs antifungals, usually with surgery.
Which part of the body is most often affected, and how does infection start?
The foot, after inoculation of soil organisms through thorn pricks or small wounds, often in people walking barefoot.
Related conditions
- Osteomyelitis
- Cellulitis of the leg
- Diabetic foot
- Leishmaniasis
- Tuberculosis
- Sepsis and septic shock
- Kaposi sarcoma
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Mycetoma (World Health Organization, 2025); Mycetoma Basics | Mycetoma | CDC (Centers for Disease Control and Prevention, 2024).
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