Question
Mycotic mycetoma
Answer
Mycotic mycetoma (eumycetoma) is the fungal form of mycetoma — a chronic, slowly progressive granulomatous infection of subcutaneous tissue, most often affecting the foot (“Madura foot”), caused by true fungi (as opposed to actinomycetoma, caused by filamentous aerobic actinomycete bacteria) — distinguishing the two is essential since treatment differs completely.
Causative organisms: Madurella mycetomatis is the most common cause worldwide, along with other fungi (e.g., Madurella grisea, Exophiala jeanselmei, Pseudallescheria boydii).
Clinical presentation: a classical triad of tumefaction (swelling), multiple sinus tracts, and discharge containing grains — eumycetoma grains are typically black or dark-coloured.
Laboratory diagnosis:
- Direct examination of grains — crushed between two slides, showing broad, septate fungal hyphae on microscopy (distinguishing from the fine, thin, branching bacterial filaments of actinomycetoma).
- Histopathology — biopsy showing the grain surrounded by neutrophilic infiltrate/granulomatous inflammation; special stains (PAS, Gomori methenamine silver) highlight fungal elements.
- Culture — on Sabouraud dextrose agar, identifying the specific causative fungal species; growth can be slow.
- Imaging (X-ray, ultrasound, MRI) — assesses bone involvement.
Treatment: prolonged antifungal therapy (itraconazole) often combined with surgical excision; eumycetoma generally has a poorer prognosis and higher recurrence rate than actinomycetoma, which typically responds better to antibacterial therapy alone.