Question
Mycetoma
Answer
Mycetoma is a chronic, slowly progressive granulomatous infection of subcutaneous tissue, most often affecting the foot (“Madura foot”), caused either by true fungi (eumycetoma) or filamentous aerobic actinomycete bacteria (actinomycetoma) — distinguishing between the two is essential, since treatment differs completely.
Clinical presentation: a classic triad of tumefaction (swelling), multiple sinus tracts, and discharge containing grains — grain colour, size, and consistency provide an important diagnostic clue.
Causative organisms:
- Eumycetoma: Madurella mycetomatis (most common), Madurella grisea, Exophiala jeanselmei, Pseudallescheria boydii — grains typically black/dark.
- Actinomycetoma: Nocardia species, Actinomadura species, Streptomyces somaliensis — grains typically white, yellow, or red.
Laboratory diagnosis:
- Direct examination of grains — crushed between slides: eumycetoma shows broad, septate fungal hyphae; actinomycetoma shows fine, thin, branching bacterial filaments.
- Histopathology — biopsy showing the grain surrounded by neutrophilic infiltrate/granulomatous inflammation; special stains (PAS, GMS for fungi; Gram/modified acid-fast for actinomycetes) differentiate the two categories.
- Culture — on Sabouraud dextrose agar (fungi) or specific media (actinomycetes), identifying the specific causative species.
- Imaging (X-ray, ultrasound, MRI) — assesses bone involvement.
- Molecular methods (PCR) — increasingly used where culture is difficult.
Treatment: actinomycetoma responds well to prolonged combination antibacterial therapy (sulfonamide plus aminoglycoside); eumycetoma requires antifungal therapy (itraconazole) often combined with surgical excision, and generally has a poorer prognosis.