Mycetoma

Mycetoma is a chronic, progressive, granulomatous infection of the subcutaneous tissue, most commonly affecting the foot (though any site of traumatic inoculation can be affected). It is caused by either fungal organisms (eumycetoma) or filamentous bacteria (actinomycetoma).

It is acquired through traumatic inoculation of the organism from contaminated soil or vegetation, typically in barefoot agricultural workers in endemic tropical and subtropical regions. The geographical distribution is often termed the "mycetoma belt," spanning parts of Africa, the Indian subcontinent and Central and South America.

It is characterised by the classical clinical triad of subcutaneous swelling, multiple sinus tracts, and discharge of characteristic grains, which are aggregates of the causative organism.

Distinguishing fungal from bacterial aetiology is essential, because the treatment approaches are fundamentally different.

Pathophysiology and classification

• Inoculation is typically through a minor penetrating injury, such as a thorn prick while barefoot. The organism establishes chronic, localised infection in the subcutaneous tissue and spreads progressively along tissue planes.
• This produces subcutaneous swelling with multiple discharging sinus tracts. The grains discharged are dense aggregates of the organism bound together by host tissue material.
• Eumycetoma (fungal mycetoma) is caused by various fungal species, including Madurella mycetomatis, the commonest single causative organism globally. It typically produces black grains. The course is generally more indolent, with a characteristically poorer response to antifungal treatment than the bacterial form.
• Actinomycetoma (bacterial mycetoma) is caused by filamentous bacteria including Nocardia, Actinomadura and Streptomyces species. Grains vary in colour (white, yellow or red depending on the organism). The response to antibiotics is generally more favourable than in the fungal form, though still often prolonged.

• The typical initial presentation is a slowly progressive, painless (or minimally painful) subcutaneous swelling, most commonly of the foot. It develops over months to years after a traumatic inoculation injury that is often unremembered or unrecognised.
• The affected area enlarges progressively. Multiple sinus tracts develop and discharge characteristic grains. Grain colour is a useful, though not definitive, clue to the organism category: black grains suggest eumycetoma and lighter grains suggest actinomycetoma.
• Established disease shows progressive tissue distortion and, in advanced disease, involvement of underlying bone (osteomyelitis).
• The disease remains localised to the site of inoculation and adjacent tissue for a prolonged period, without the systemic spread or constitutional symptoms of many other chronic infections. Local tissue destruction and deformity can nevertheless be severe, and secondary bacterial infection of the chronically discharging sinus tracts is a recognised complication.
• Untreated, progressive disease can cause severe limb deformity and significant functional impairment. In longstanding, advanced cases it may necessitate amputation. Early recognition and treatment are therefore important.

• Examine discharged grains by direct microscopy or, more definitively, by histopathology of a biopsy specimen. Grain and organism morphology distinguish fungal (eumycetoma) from bacterial (actinomycetoma) causation, a critical distinction because the treatment approaches are fundamentally different.
• Culture of grain material is technically challenging and needs prolonged incubation, particularly for fungi. Where successful, it gives definitive species level identification. Molecular polymerase chain reaction based techniques are increasingly used for more rapid, specific identification where available.
• Ultrasound can show characteristic findings supporting the diagnosis and assess the extent of subcutaneous involvement.
• Plain radiography or, for more detail, magnetic resonance imaging assesses bone involvement, which is essential for staging and treatment planning.
• In endemic regions, other chronic granulomatous conditions overlap geographically and clinically, including chromoblastomycosis and certain other deep fungal infections. With bone involvement, chronic osteomyelitis from other causes is also a differential.
• Confirm mycetoma and its fungal or bacterial subtype before committing to a prolonged treatment course.

• Actinomycetoma (bacterial mycetoma) is treated with prolonged combination antibiotic therapy. Regimens vary with the causative organism and local protocols.
• Commonly, trimethoprim with sulfamethoxazole is combined with an aminoglycoside (such as amikacin or streptomycin) for an initial period. This is followed by prolonged oral combination therapy, often trimethoprim with sulfamethoxazole combined with rifampicin or another agent. Total duration frequently extends to many months to a year or longer, guided by clinical response.
• Eumycetoma (fungal mycetoma) is treated with prolonged antifungal therapy, with itraconazole a commonly used first-line agent. Response is generally less favourable and more protracted than for actinomycetoma, frequently needing a year or more of treatment.
• Antifungal treatment alone has generally limited efficacy in eumycetoma, so it is often combined with surgical excision of affected tissue.
• Surgery ranges from localised excision to more radical debridement in advanced, extensive disease unresponsive to medical treatment alone. In severe cases with extensive destruction not amenable to conservative management, amputation is required.
• Surgery is particularly important in eumycetoma and may also be needed as an adjunct in extensive or treatment-refractory actinomycetoma.
• Treatment is prolonged and the condition frequently occurs in resource-limited settings. Adherence support, monitoring for adverse effects of prolonged courses of potentially toxic antimicrobials, and regular reassessment of response are essential.
• Early diagnosis and treatment, before extensive tissue destruction and bone involvement, substantially improve the likelihood of success with more limited surgery.
• Community education and healthcare access in endemic regions support earlier presentation and diagnosis. Rehabilitation addresses residual functional impairment after treatment of more advanced disease.