Question
Etiology, clinical features and laboratory diagnosis of Mycetoma
Answer
Mycetoma
Etiology: a chronic, progressive, granulomatous subcutaneous infection caused by either true fungi (eumycetoma) — e.g., Madurella mycetomatis — or filamentous, higher bacteria/actinomycetes (actinomycetoma) — e.g., Nocardia species, Actinomadura, Streptomyces. Acquired via traumatic inoculation (e.g., a thorn prick) with soil-derived organisms.
Clinical features: classically affects the foot (“Madura foot”), or occasionally the hand, characterized by the triad of tumefaction (progressive, non-tender swelling), multiple sinus tracts, and discharge containing “grains” (granules) — compact colonies of the causative organism, whose colour (black, white, yellow, red) can provide a clue to the likely causative agent. The infection progresses slowly over years, potentially involving underlying bone.
Laboratory diagnosis:
- Direct examination of grains — crushed and examined microscopically; eumycetoma grains show broad, septate fungal hyphae, while actinomycetoma grains show fine, thin (<1 μm), Gram-positive branching filaments.
- Gram stain and Modified Ziehl-Neelsen stain of crushed grains — helps distinguish actinomycetoma (Gram-positive filaments, variably acid-fast for Nocardia) from eumycetoma.
- Culture — grains cultured on Sabouraud dextrose agar (for fungi) and appropriate bacteriological media (for actinomycetes), for definitive species identification — essential since treatment differs substantially (antibacterial for actinomycetoma vs antifungal for eumycetoma).
- Histopathology — biopsy showing granulomatous inflammation with grains, using special stains (PAS/GMS for fungal elements).
- Imaging (X-ray/MRI) — assesses bone involvement and extent of disease.
Treatment: actinomycetoma responds well to prolonged combination antibacterial therapy (e.g., Streptomycin plus Cotrimoxazole); eumycetoma is generally less responsive to antifungal therapy and often requires surgical intervention.