Mycetoma Workup

Updated: Jan 09, 2017
  • Author: Folusakin O Ayoade, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
  • Print
Workup

Approach Considerations

Currently, multiple diagnostic tools are used to determine the extent of infections and to identify the causative agents of mycetoma. These include various imaging, cytological, histopathological, serological, and culture techniques; phenotypic characterization; and molecular diagnostics. [13]

Next:

Imaging Studies

Bone radiography

Only 3% of patients with mycetoma have normal radiographs. [14]

Once mycetoma has invaded the bone, the following changes may be observed:

  • Cortical thinning is due to compression from the outside by the mycetoma.

  • Cortical hypertrophy or periosteal proliferation may present as a sunray appearance and a Codman triangle.

  • Multiple lytic lesions or cavities may be large and few in number with well-defined margins (eumycetoma) or small and numerous with ill-defined margins (actinomycetoma).

  • Disuse osteoporosis may occur in late stages mycetoma.

Bone involvement has been radiographically classified, as follows:

  • Stage 0 - Soft-tissue swelling without bone involvement

  • Stage I - Extrinsic pressure effects on the intact bones in the vicinity of an expanding granuloma

  • Stage II - Irritation of the bone surface without intraosseous invasion

  • Stage III - Cortical erosion and central cavitation

  • Stage IV - Longitudinal spreading along a single ray

  • Stage V - Horizontal spread along a single row

  • Stage VI - Multidirectional spread due to uncontrolled infection

MRI

MRI helps with the differential diagnosis and the assessment of the degree of bone and soft-tissue involvement. [15] The dot-in-circle sign is an easy-to-recognize and highly specific MRI sign of mycetoma. [16, 17]

MRI coronal section of mycetoma in a 47-year-old s MRI coronal section of mycetoma in a 47-year-old shepherd from Mauritania who had a painless progressive swelling of the face for more than 20 years. On this T1-potentiated image, a large heterogenous mass surrounds the cranium. Bone invasion can be observed only in the area of the zygomatic fossa.
MRI with coronal view of mycetoma in a 47-year-old MRI with coronal view of mycetoma in a 47-year-old shepherd from Mauritania who had a painless progressive swelling of the face for more than 20 years. The mycetoma mass invades the left parapharyngeal space and almost reaches the lumen of the pharynx.

Ultrasonography

Single or multiple thick-walled cavities with hyperreflective echoes and no acoustic enhancement are always observed with mycetoma, whereas these features are not demonstrated in nonmycetoma swellings.

In eumycetoma, the hyperreflective echoes are sharp, corresponding to the grains in the lesion.

In actinomycetoma, the hyperreflective echoes are fine and closely aggregated and commonly settle at the bottom of the cavities.

CT scanning

This modality provides a better detail of changes than conventional radiography.

Previous
Next:

Procedures

Perform a deep wedge biopsy or puncture and fine-needle aspiration to obtain a grain sample. The aspirated material is processed to form cell blocks and further studied for routine tissue histopathological examination. [18] Fine-needle aspiration cytology allows differentiating actinomycetoma from eumycetoma. [19]

Previous
Next:

Histologic Findings

Grains are surrounded closely and sometimes infiltrated by neutrophils and can be easily seen on histologic sections. In biopsy samples, staining with Gram stain (actinomycetoma) or Gomori methenamine silver or periodic acid-Schiff stains (eumycetoma) could help in identifying the causal agent. For mycetomas in which causative infectious agents cannot be isolated, histology may prove beneficial by avoiding inadvertent use of combined antifungal and antimicrobial agents so that a correct therapeutic modality can be decided. [20]

Previous
Next:

Staging

Radiographic staging of bone involvement can be found in Imaging Studies.

Previous
Next:

Lab Studies

Staining

Hematoxylin-eosin staining of a biopsy sample allows for detection of mycetoma grains.

Process hematoxylin-eosin and May-Grünwald-Giemsa staining of a cytologic smear of a sample obtained via fine-needle aspiration. Mycetoma grains can be distinguished from artifacts and other organisms by the intimate relationship between the grain and neutrophils. The appearance of the grains is as follows:

  • Actinomycetoma - Homogenously eosinophilic with hematoxylin-eosin stain; blue in the center with pink filaments in the periphery with May-Grünwald-Giemsa stain

  • Eumycetoma - Brownish color with hematoxylin-eosin stain; black with a green tinge with May-Grünwald-Giemsa stain

The causal agent of each type of mycetoma can be visualized better with the following:

  • Tissue Gram stain to detect fine, gram-positive, branching filaments within the actinomycetoma grain

  • Gomori methenamine silver or periodic acid-Schiff stain to demonstrate the larger hyphae of eumycetoma

Evaluation of the characteristics of the associated granules suggests an initial differential diagnosis, as follows:

  • White-to-yellow grains indicate P boydii (S apiospermum), Nocardia species, or A madurae infection.

  • Yellow-to-brown grains indicate S somaliensis infection.

  • Black grains indicate Streptomyces paraguayensis, Madurella species, or Leptosphaeria species infection.

  • Red-to-pink grains indicate A pelletieri infection.

Culture

Culture the grains obtained from a deep wedge biopsy or a sample obtained via puncture and fine-needle aspiration. The primary isolation media used should be Löwenstein-Jensen for actinomycetoma or blood agar for eumycetoma.

Superficial samples of the draining sinuses are inadequate for culture because of frequent contamination with bacteria.

Serology

Serologic diagnosis is available in a few centers and can be helpful in some cases for diagnosis or follow-up care during medical treatment. Antibodies can be determined via (1) immunodiffusion, (2) counterimmunoelectrophoresis, (3) enzyme-linked immunosorbent assay, or (4) Western blot.

Previous