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Mycetoma

Q: What conditions should be included in the differential diagnosis of mycetoma?

For subcutaneous mycetoma, differential diagnosis includes hemangioma: the visual MRI appearance of mycetoma can mimic a hemangioma. A definitive diagnosis requires confirmation by biopsy.

For medical students2 min readUpdated 2026-10-10

Mycetoma (also known as Madura foot) is a chronic granulomatous inflammatory disease of the subcutaneous tissue with a tendency to deeply invade adjacent structures. The pathological process progressively destroys fascia, muscle architecture, and bone, leading to severe deformities.

EndemicityPredominantly occurs in tropical and subtropical regions.

PathogensTrue fungi (eumycotic form) or actinomycetes (actinomycetoma).

Key markerPresence of multicolored granules ("grains") measuring 0.5 to 2 mm in the pus.

Treatment approachAntifungal therapy (itraconazole) combined with surgical tissue resection.

Etiology and Classification

Depending on the nature of the pathogen, mycetoma is traditionally divided into two major groups:

Eumycotic mycetoma. Caused by true fungi, predominantly dematiaceous (darkly pigmented) species. The most significant pathogen is Pseudallescheria boydii. Other causative agents include Madurella grisea, Acremonium (Cephalosporium) falciforme, Scedosporium apiospermum, and Exophiala jeanselmei.
Actinomycetoma. Caused by bacterial agents—actinomycetes. This group includes members of the genera Actinomyces, Nocardia, Streptomyces, and Actinomadura.

The natural reservoir for all these microorganisms is soil and vegetation.

Pathogenesis and Clinical Presentation

The primary route of infection is contact. The pathogen enters the body through an entry portal, which is typically traumatized skin. Much less commonly, infection occurs via an airborne route involving the respiratory tract.

Due to the mechanism of infection (contact with soil), the lower extremities—especially the feet—are the most frequent site of involvement. This is why the classic form of the disease is often called "Madura foot".

Pathology development dynamics:

Primary papules form at the site of pathogen inoculation.
Gradually, dense deep nodules develop, which suppurate to form abscesses.
The purulent process extends deeply, causing total destruction of deep tissues—fascia, muscles, and bone structures are destroyed.
Concurrently, there is active proliferation of fibrous tissue.

In the final stages of the disease, massive edema and marked, disabling deformation of the affected foot develop.

Microbiological Diagnostics

To confirm the diagnosis, purulent discharge or tissue biopsy samples are sent to the laboratory. The standard baseline method is microscopy of a native preparation treated with potassium hydroxide (KOH).

The primary diagnostic sign is the detection of multicolored granules (so-called "grains") ranging in size from 0.5 to 2 mm within the sample.

Microscopic etiology differentiation:

Fungal origin: Thick septate hyphae and chlamydoconidia are visualized in the preparation. It is important to note that the hyphae of P. boydii are morphologically extremely similar to fungal elements of the genus Aspergillus. In its sexual stage, P. boydii forms cleistothecia (100–200 µm in size)—upon rupture, characteristic pale-brown elliptic ascospores are released into the environment.
Bacterial (actinomycetal) origin: Specific sulfur granules composed of thin branching bacterial filaments are identified in the field of view.

Frequently asked questions

What is the medical management strategy for various forms of mycetoma?

Medical treatment for mycetoma includes the use of antifungals.

Itraconazole is indicated for the treatment of mycetoma.

In addition to medical therapy, surgical intervention—resection of affected tissues—is utilized. Data on specific pharmacotherapy for actinomycetoma are not provided in the source.

What culture media are used for the culture diagnosis of mycetoma pathogens?

Sabouraud agar is indicated for fungi. Eumycotic mycetoma is caused by true fungi, predominantly dematiaceous species. Data on specific nutrient media dedicated specifically to mycetoma culture diagnosis, as well as media for bacterial actinomycete agents, are not provided in the sources.

What conditions should be included in the differential diagnosis of mycetoma?

For subcutaneous mycetoma, differential diagnosis includes hemangioma: the visual MRI appearance of mycetoma can mimic a hemangioma. A definitive diagnosis requires confirmation by biopsy.

What imaging modalities are used to assess the degree of bone destruction in mycetoma?

MRI is described for the imaging diagnosis of mycetoma. Modalities used include:

T1-weighted scans;
STIR sequence with fat suppression;
T2-weighted scans;
T1-weighted scans with fat suppression and contrast enhancement.

T2-weighted images show multiple low-signal rings with central low-signal dots; contrast administration reveals multiple intense ring-like enhancements. A typical sign of mycetoma is the "dot-in-circle" sign. A definitive diagnosis requires biopsy confirmation. Ultrasound, fluoroscopy, or CT may be used to guide percutaneous bone or soft tissue biopsies.

What serves as the reservoir for mycetoma pathogens?

The natural reservoir of the microorganisms causing the disease is the environment—soil and vegetation.

What is the main microscopic difference between eumycotic mycetoma and actinomycetoma?

In fungal etiology, septate hyphae and chlamydoconidia are identified in the sample, whereas in actinomycetal etiology, granules (sulfur granules) and thin branching bacterial filaments are seen.

Which fungus can the hyphae of Pseudallescheria boydii be mistaken for?

Morphologically, the hyphae of P. boydii closely resemble elements of mold fungi of the genus Aspergillus.

Go deeper

Morphological features of dematiaceous fungi
Structure and formation of cleistothecia in Pseudallescheria boydii
Differential diagnosis of mycetoma versus bacterial osteomyelitis
Surgical management specific to "Madura foot"