Mycetoma fungi

Introduction

Mycetoma fungi is a chronic, granulomatous infection of the skin, subcutaneous tissue, and sometimes deeper structures like bone. It is characterized by the formation of tumor-like masses, sinus tracts, and the discharge of grains (microcolonies of causative organisms).

Types:

• • • Eumycetoma: Caused by fungi.
    • Actinomycetoma: Caused by filamentous bacteria (actinomycetes).
  • The term “Madura foot” is often used because the disease frequently affects the foot and was first described in Madurai, India.

 

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Epidemiology

1. Geographic Distribution:
   • • Mycetoma is endemic in tropical and subtropical regions, often referred to as the “mycetoma belt”, which includes:
       • Sudan, India, Mexico, Venezuela, and parts of Africa, Asia, and Latin America.
     • Eumycetoma is more common in Africa.
     • Actinomycetoma is prevalent in Central and South America, India, and the Middle East.
2. Reservoir:
   • • Soil, decaying organic material, and plant debris.
3. Mode of Transmission:
   • • Traumatic inoculation of the causative agent through wounds, cuts, or punctures (e.g., stepping on sharp objects, thorns, or splinters).
     • No person-to-person transmission.
4. At-Risk Populations:
   • • Farmers, agricultural workers, and individuals exposed to soil and plant material are at higher risk.
     • More common in males, likely due to occupational exposure.
5. Incidence:
   • • Rare in developed countries but a significant public health concern in endemic areas.

 

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Pathogenesis

1. Traumatic Inoculation:
   • • The causative organism enters the skin and subcutaneous tissues through a break in the skin.
2. Microcolony Formation:
   • • Organisms form grains (microcolonies) surrounded by neutrophils, macrophages, and a fibrotic capsule.
3. Chronic Inflammation:
   • • Persistent inflammation leads to the formation of granulomas and sinus tracts.
     • The infection slowly spreads to deeper tissues, including fascia, tendons, and bones, causing extensive damage.
4. Granuloma Formation:
   • • A granulomatous immune response attempts to contain the infection.
     • Eumycetoma elicits a more robust granulomatous response compared to actinomycetoma.
5. Dissemination:
   • • Rare but hematogenous or lymphatic spread to distant organs may occur in immunosuppressed patients.

 

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Clinical Manifestations

The clinical course is slow and indolent, with symptoms developing over months to years.

1. Classic Triad:
   • • Swelling: A painless, localized mass or swelling of the affected area (often the foot or hand).
     • Sinus tracts: Draining sinuses develop over time.
     • Discharge of grains: Yellow, white, black, or red grains (microcolonies) are exuded from the sinuses, depending on the causative organism.
2. Commonly Affected Sites:
   • • Feet (most common), hands, legs, and back.
3. Eumycetoma vs. Actinomycetoma:
   • • Eumycetoma:
       • Caused by fungi like Madurella spp., Exophiala, Curvularia, etc.
       • Progresses slowly and causes more fibrotic tissue and larger grains.
     • Actinomycetoma:
       • Caused by bacteria like Nocardia, Actinomyces, or Streptomyces.
       • More aggressive, with faster spread and more purulent discharge.
4. Complications:
   • • Bone invasion: Osteomyelitis.
     • Deformities and loss of function in the affected limb.
     • Secondary bacterial infections.

 

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Laboratory Diagnosis

Accurate diagnosis requires microbiological, histopathological, and radiological investigations.

1. Clinical Diagnosis

• • Observation of swelling, sinus tracts, and characteristic grain discharge provides strong diagnostic clues.

2.  Microscopy

• • Specimens: Grains or discharge from sinuses.
  • Procedure:
    • Direct Examination:
      • KOH mount or wet mount of grains.
      • Eumycetoma grains are pigmented (black, brown) or pale.
      • Actinomycetoma grains are white, yellow, or red.
    • Stains:
      • Gram stain: Actinomycetoma organisms appear gram-positive.
      • Lactophenol cotton blue: Fungi appear as pigmented hyphae.

3. Culture

• • Specimens: Grains, pus, or tissue biopsy.
  • Media:
    • Actinomycetes: Grows on Sabouraud dextrose agar, brain-heart infusion agar, or blood agar.
    • Fungi: Grows on Sabouraud dextrose agar or potato dextrose agar.
  • Growth Characteristics:
    • Actinomycetes: Faster growth (7–10 days).
    • Fungi: Slow growth (2–6 weeks).

4. Histopathology

• • Biopsy Specimens: Tissue surrounding grains.
  • Findings:
    • Granulomas with microcolonies surrounded by inflammatory cells.
    • Stains like H&E, PAS, and Gomori methenamine silver (GMS) reveal fungal hyphae or bacterial filaments.

5. Molecular Diagnostics

• • PCR: Used to identify fungal or bacterial DNA.
  • Useful for rapid, specific identification.

6. Imaging

• • X-ray:
    • Shows soft tissue swelling and bone involvement (osteomyelitis).
  • Ultrasound:
    • Detects subcutaneous masses and sinus tracts.
  • MRI/CT:
    • Provides detailed images of soft tissue and bone invasion.

 

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Common Causative Organisms

Eumycetoma (Fungal):

• • Madurella mycetomatis
  • Exophiala jeanselmei
  • Curvularia lunata
  • Scedosporium apiospermum

Actinomycetoma (Bacterial):

• • Nocardia brasiliensis
  • Actinomadura madurae
  • Actinomadura pelletieri
  • Streptomyces somaliensis