Introduction
- Mycetoma is a long-term (chronic) infectious disease that mainly affects the skin, tissues under the skin (subcutaneous tissue), muscles, and bones.
- It usually starts after a small injury, such as a thorn prick, splinter, or cut, which allows microorganisms to enter the body.
The disease develops slowly and is characterized by three main features:
- A painless swelling (lump)
- Multiple draining sinuses (small openings in the skin)
- Discharge of colored grains (small granules containing the infecting organism)
There are two types of mycetoma:
- Eumycetoma – caused by fungi.
- Actinomycetoma – caused by filamentous bacteria.
Although both types have similar symptoms, their treatment is different. This article mainly discusses eumycetoma (fungal mycetoma).
What is Eumycetoma?
- Eumycetoma is a chronic fungal infection caused by different species of fungi.
- These fungi are naturally found in soil, dust, thorny plants, wood, and decaying plant material.
- The infection begins when fungal spores enter the body through a small injury, such as a thorn prick, splinter, cut, or puncture wound.
- Once inside the skin, the fungi grow slowly in the tissues beneath the skin.
Etiological Agents
Many fungi can cause eumycetoma, but only a few species are responsible for most cases worldwide.
| Fungus | Grain Color | Geographic Distribution |
|---|---|---|
| Madurella mycetomatis | Black | Africa, India, Middle East |
| Madurella grisea | Black | India, Africa |
| Trematosphaeria grisea | Black | Tropical countries |
| Falciformispora senegalensis | Black | Africa |
| Scedosporium apiospermum | White | Worldwide |
| Acremonium species | White | Tropical regions |
| Fusarium species | White | Worldwide |
Important Fungi
Madurella mycetomatis
- Most common cause of eumycetoma worldwide.
- Produces black-colored grains.
- Common in Africa, India, and the Middle East.
- Can spread to bones if not treated.
Madurella grisea
- Produces black grains.
- Causes slow-growing infections of the feet and legs.
- Less common than Madurella mycetomatis.
Trematosphaeria grisea
- Produces black grains.
- Causes chronic infection of the skin and underlying tissues.
Falciformispora senegalensis
- Mainly found in Africa.
- Produces black grains.
- Can cause severe tissue damage.
Scedosporium apiospermum
- Produces white grains.
- Found in many countries.
- May be resistant to some antifungal medicines.
Acremonium species
- Produce white grains.
- Usually enter the body after skin injury.
Fusarium species
- Common fungi found in soil.
- Produce white grains.
- Sometimes cause serious infections in people with weak immunity.
Epidemiology
- Mycetoma is mainly found in hot and dry tropical and subtropical regions of the world.
- The area where the disease is most common is called the “Mycetoma Belt.”
Countries with many reported cases include:
- Sudan
- India
- Mexico
- Senegal
- Somalia
- Yemen
- Ethiopia
- Chad
People at higher risk include:
- Farmers
- Agricultural workers
- Shepherds
- Gardeners
- Construction workers
- People who walk barefoot
Risk Factors
Several factors increase the chance of developing eumycetoma.
- Walking Barefoot – Walking without shoes is the biggest risk factor because the feet can easily be injured by thorns or sharp objects contaminated with fungi.
- Thorn Injuries – Thorns from plants, especially acacia trees, can carry fungal spores into the skin.
- Agricultural Work – People working in farms regularly come into contact with soil and plants that contain fungi.
- Repeated Skin Injuries – Small cuts, puncture wounds, splinters, and scratches make it easier for fungi to enter the body.
- Rural Living – People living in villages have more exposure to soil and often have limited access to healthcare.
- Warm and Dry Climate – The fungi grow well in hot, dry environments, making these regions more suitable for the disease.
- Poor Protective Clothing – Not wearing shoes, boots, or gloves while working increases the risk of infection.
Mode of Transmission
Mycetoma does not spread from one person to another. It is not a contagious disease.
The infection occurs when fungal spores enter the body through broken skin.
Common ways the fungus enters the body include:
- Thorn pricks
- Splinter injuries
- Cuts
- Puncture wounds
- Soil-contaminated injuries
- Contact with infected plant materials
The fungi are directly implanted into the skin, where they slowly grow and cause infection.
There is no evidence that mycetoma spreads through:
- Touching an infected person
- Coughing or sneezing
- Blood transfusion
- Food or drinking water
Pathogenesis
The disease develops slowly in several steps.
Step 1: Entry of the Fungus
The fungus enters the skin through a small injury such as a thorn prick or cut.
Step 2: Growth in the Tissue
The fungi begin to grow slowly in the tissues beneath the skin.
Step 3: Body’s Immune Response
The immune system reacts to the fungi, causing long-term inflammation.
Step 4: Formation of Fungal Grains
The fungi form small compact colonies called grains, which are surrounded by inflammatory cells.
Step 5: Formation of Sinus Tracts
As the infection grows, abscesses develop and eventually open through the skin, forming multiple draining sinuses.
Step 6: Spread of Infection
Without treatment, the infection spreads to nearby muscles, joints, and bones. This may lead to bone destruction, deformity, difficulty walking, and permanent disability.
Laboratory Diagnosis
1. Clinical Examination
The first step in diagnosis is a careful clinical examination by the doctor.
The doctor asks about:
- Duration of swelling
- History of thorn prick or skin injury
- Occupation (farmer, gardener, laborer, etc.)
- Residence in tropical or rural areas
- Previous treatment history
During the physical examination, the doctor looks for:
- Painless swelling
- Multiple draining sinus tracts
- Discharge of black or white grains
- Size and location of the lesion
- Signs of bone involvement
- Joint deformity or restricted movement
The presence of the classical triad—painless swelling, multiple sinuses, and grain discharge—strongly suggests mycetoma.
2. Specimen Collection
A good-quality specimen is essential for an accurate diagnosis.
Common specimens include:
- Pus from draining sinuses
- Fungal grains discharged from the lesion
- Deep tissue biopsy
- Fine-needle aspiration (FNA) from the swelling
Collection Tips
- Collect the specimen using sterile techniques.
- Fresh grains should be collected before starting antifungal treatment.
- Deep tissue biopsy usually provides the best sample for diagnosis.
The collected specimen is used for microscopy, culture, and histopathological examination.
3. Gross Examination of Grains
The discharged grains are examined with the naked eye or under a stereomicroscope.
Important features include:
- Color (black, white, or yellow)
- Size
- Shape
- Consistency
Significance of Grain Color
| Grain Color | Common Organisms |
|---|---|
| Black | Madurella mycetomatis, Madurella grisea |
| White | Scedosporium apiospermum, Acremonium, Fusarium |
| Yellow | Rare; may occur in mixed infections |
The color of the grains provides an important clue about the causative organism.
4. Direct Microscopy
- Direct microscopic examination is a simple and rapid method for detecting fungal elements.
- Potassium Hydroxide (10–20% KOH) Mount
- The grains or tissue are placed on a glass slide with 10–20% potassium hydroxide (KOH).
- KOH dissolves tissue debris while leaving fungal structures intact, making them easier to observe under the microscope.
Microscopic Findings
- Septate fungal hyphae
- Thick, branching hyphae
- Pigmented fungal filaments (in black-grain fungi)
- Compact fungal grains
KOH examination provides a quick preliminary diagnosis but cannot accurately identify the fungal species.
5. Histopathological Examination
- Histopathology is one of the most important methods for confirming eumycetoma.
- A tissue biopsy is collected from the lesion and examined under a microscope after staining.
Common Stains Used
- Hematoxylin and Eosin (H&E): Shows tissue structure and inflammatory response.
- Periodic Acid–Schiff (PAS): Highlights fungal cell walls in bright magenta.
- Gomori Methenamine Silver (GMS): Clearly stains fungal hyphae black, making them easy to identify.
Histopathological Findings
Typical findings include:
- Granulomatous inflammation
- Fungal hyphae within grains
- Neutrophils surrounding the grains
- Multinucleated giant cells
- Fibrosis (scar tissue)
- Splendore–Hoeppli phenomenon (eosinophilic material surrounding the fungal grains)
Histopathology also helps differentiate eumycetoma from actinomycetoma and other chronic skin infections.
6. Fungal Culture
Fungal culture is considered the gold standard for identifying the causative fungus.
Culture Medium
The specimen is inoculated onto:
- Sabouraud Dextrose Agar (SDA) (with or without antibiotics)
Other fungal media may also be used if required.
Incubation
- Temperature: 25–30°C
- Duration: 2–6 weeks, depending on the fungal species
Some fungi grow slowly and require prolonged incubation.
Culture Findings
The laboratory observes:
- Colony color
- Texture
- Growth rate
- Pigmentation
- Microscopic appearance of fungal structures
These features help identify the fungal species responsible for the infection.
7. Molecular Diagnosis
Molecular techniques provide rapid and accurate identification of the causative fungus.
Common methods include:
- Polymerase Chain Reaction (PCR)
- DNA sequencing
- Real-Time PCR
Advantages
- High accuracy
- Rapid identification
- Detects fungi that grow poorly in culture
- Helps identify uncommon fungal species
- Useful in difficult or recurrent cases
Although highly reliable, molecular tests are expensive and may not be available in all laboratories.
8. Imaging Studies
Imaging is performed to determine how far the infection has spread, especially to muscles and bones.
X-ray
X-rays help detect:
- Bone destruction
- Osteomyelitis
- Bone cavities
- Bone deformity
Ultrasound
Ultrasound is useful for:
- Detecting abscesses
- Identifying sinus tracts
- Demonstrating the characteristic “dot-in-circle sign,” which is highly suggestive of mycetoma.
Computed Tomography (CT Scan)
CT scans provide detailed images of:
- Bone involvement
- Extent of tissue destruction
- Surgical planning
Magnetic Resonance Imaging (MRI)
MRI is the best imaging method for evaluating:
- Soft tissue involvement
- Muscle invasion
- Tendon involvement
- Bone marrow infection
- Extent of disease before surgery
9. Differential Laboratory Diagnosis
Laboratory tests also help distinguish eumycetoma from diseases with similar symptoms, including:
- Actinomycetoma
- Chronic osteomyelitis
- Tuberculosis
- Sporotrichosis
- Chromoblastomycosis
- Botryomycosis
- Soft tissue tumors