Figure 27.1 Eumycetoma in a 35-year-old black male, showing a distorted foot with multiple nodules and sinuses.

Differential diagnosis

There are several other conditions that need to be taken into account that can mimic eumycetoma, hence the need for biopsy and culture. These are:

• Foreign-body granulomas
  
• Soft-tissue neoplasms
  
• Tumors, e.g., Kaposi’s sarcoma
  
• Other deep fungal infections, e.g., sporotrichosis; chromomycosis, conidiobolomycosis
  
• Cysts
  
• Botryomycosis
  
• Leishmaniasis
  
• Tuberculosis.

Diagnosis

Histopathology

Histologically the lesions are characterized by granulomatous inflammation with organisms within the center of the abscesses. Occasionally maze-shaped structures called clubs are found in the vicinity of the granules.The clinical presentation of mycetoma remains the same irrespective of the implicated organism, although the histologic features, namely the size, shape, and color of the granules can be suggestive of the causative agent. Using special stains (Grocott, periodic acid–Schiff, and hematoxylin and eosin) assists in ascertaining the various types of grain. Fine-needle aspiration is an alternative to obtaining samples for cytology.

Laboratory diagnosis

Direct examination, culture, and histopathology are the various methods that are used to identify the causative species and genus. Suggestions of the etiologic agent can be drawn from the size, form, presence or absence of clubs or pseudoclubs. The most commonly isolated organism in eumycetoma is Madurella mycetomatis, with countries such as Sudan reporting up to 70% of cases.

Contamination of cultures with bacteria, as well as challenges in identifying the morphology of the organism when cultures are positive, can sometimes pose a problem in diagnosing the genus and species when studying pathology specimens. This has led to the introduction of various methods of molecular diagnostic techniques, for example polymerase chain reaction (PCR) amongst which are PCR restriction fragment length polymorphism (RFLP), real-time PCR, and DNA sequencing, and these have been used to identify the species of eumycetoma from lesional biopsies and the environment.

Below we describe a few of the common organisms.

Madurella mycetomatis

Inspection reveals oval, spherical, or lobulated black grains measuring 0.5 to 1 mm which sometimes coalesce to form 5-mm oval grains. Hyphae are light brown, ranging from 1 to 5 mm in diameter with reddish–brown grains on microscopy.

Culture

Initially the hyphae look white and membranous, and then later change to yellow-brown with a dark pigment that spreads into the culture medium. Growth is at 26 to 30°C. Oval conidia (3.5–5 µm) are produced and these are derived from the simple or branched conidiophores.

Madurella grisea

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