Etiology and classification
Depending on the nature of the pathogen, mycetoma is traditionally divided into two large groups:
- Eumycotic mycetoma. Caused by true fungi, among which dematiaceous (dark-pigmented) species predominate. The most significant pathogen is considered to be Pseudallescheria boydii. The pathology can also be triggered by Madurella grisea, Acremonium (Cephalosporium) falciforme, Scedosporium apiospermum, and Exophiala jeanselmei.
- Actinomycetoma. Caused by bacterial agents—actinomycetes. This group includes representatives of the genera Actinomyces, Nocardia, Streptomyces, and Actinomadura.
The natural reservoir for all the listed microorganisms is soil and plants.
Pathogenesis and clinical presentation
The primary route of transmission is contact. The pathogen enters the body through the portal of entry—damaged areas of the skin. Airborne transmission, which involves the respiratory tract, is significantly less common.
Due to the mechanism of infection (contact with soil), the lower extremities, especially the feet, become the favored localization of the process. For this reason, the classical form of the disease is often called "Madura foot".
Dynamics of pathological development:
- Primary papules form at the site of pathogen introduction.
- Gradually, dense deep-seated nodules develop, which break down to form abscesses.
- The purulent process spreads inward, causing total destruction of deep tissues—fascia, muscles, and bone structures are destroyed.
- In parallel, active proliferation of fibrous tissue occurs.
In the final stage of the disease, massive edema and severe, disabling deformation of the affected foot develop.
Microbiological diagnostics
To confirm the diagnosis, purulent discharge or a biopsy of the affected tissues is sent to the laboratory. The basic method is microscopy of a native specimen treated with potassium hydroxide (KOH) solution.
Main diagnostic sign — the detection of multicolored granules (so-called "grains") ranging in size from 0.5 to 2 mm in the studied material.
Differentiation of etiology under the microscope:
- Fungal nature: thick septate hyphae and chlamydospores are visualized in the specimen. It is important to remember that the hyphae of P. boydii are morphologically extremely similar to fungal elements of the genus Aspergillus. In the sexual stage, P. boydii forms cleistothecia (100–200 µm in size)—upon their rupture, characteristic pale-brown elliptic ascospores are released into the environment.
- Bacterial (actinomycetic) nature: specific granules (sulfur granules) consisting of thin branching bacterial filaments are identified in the field of view.
Briefly: answers to topical questions
What is the medical treatment strategy for various forms of mycetoma?
Medical treatment of mycetoma, according to the source, includes the use of antimycotics.
- Itraconazole is listed as a drug for the treatment of mycetoma.
In addition to drug therapy, surgical intervention—resection of affected tissues—is used. There is no data on specific drug tactics for actinomycetoma in the provided sources.
Which culture media are used for the culture diagnosis of mycetoma pathogens?
The provided sources indicate that Sabouraud agar is used for fungi. Eumycotic mycetoma is caused by true fungi, predominantly dematiaceous ones. Data on specific culture media specifically for the culture diagnosis of mycetoma, as well as media for bacterial agents of actinomycetoma, are not presented in the sources.
What diseases must mycetoma be differentiated from?
For subcutaneous mycetoma, differential diagnosis with hemangioma is indicated in the sources: the visual MRI picture of mycetoma can mimic hemangioma. The definitive diagnosis requires confirmation by biopsy.
What diagnostic imaging methods are used to assess the degree of bone destruction in mycetoma?
For imaging diagnostics of mycetoma, MRI is described in the sources. The following are used:
- T1-weighted scans;
- STIR sequence with fat suppression;
- T2-weighted scans;
- T1-weighted scans with fat suppression and contrast enhancement.
On T2-weighted images, multiple rings of low MR signal with central low-signal dots are determined; upon contrast administration, multiple intense ring-like contrast enhancement is observed. A typical sign of mycetoma is the "dot-in-ring" sign. The definitive diagnosis requires biopsy confirmation. Ultrasound, fluoroscopy, or CT can be used for navigation during percutaneous bone or soft tissue biopsy.
Class and exam questions
What serves as the reservoir for mycetoma pathogens?
The natural reservoir of the disease-causing microorganisms is the environment—soil and vegetation.
What is the main microscopic difference between eumycotic mycetoma and actinomycetoma?
In fungal etiology, septate hyphae and chlamydospores are determined in the specimen, while in actinomycetic etiology, granules and thin branching bacterial filaments are found.
Which fungus can Pseudallescheria boydii hyphae be confused with?
Morphologically, P. boydii hyphae closely resemble elements of mold fungi of the genus Aspergillus.
What else to study on this topic
- Morphological features of dematiaceous fungi
- Structure and formation of cleistothecia in Pseudallescheria boydii
- Differential diagnosis of mycetoma with bacterial osteomyelitis
- Specifics of surgical tactics for "Madura foot"
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