Subcutaneous Mycoses

Mycetoma (also called “madura foot” after being first described in the Madurai district of southern India) is a chronic infection of the skin and subcutaneous tissues due to fungi (eumycetoma) or bacteria of the order actinomycetes (actinomycetoma). Yes, you read it correctly. Mycetomas can be due to either fungi or bacteria. They are defined by three hallmark features: i) presence of sinus tracts; ii) discharge of “grains” (hard protective structures produced by the causative organisms which ooze out of the sinus tracts); iii) painless subcutaneous swelling/masses. This is high-yield!  

Mycetomas occur across dry tropical and subtropical areas of the world. High incidence is seen within the mycetoma belt, including North and Central Africa (e.g., Sudan, Chad, Ethiopia, Senegal, Somalia), Middle East (e.g., Yemen), India, and Latin America (e.g., Mexico, Venezuela). Humans acquire mycetomas through cutaneous implantation from saprophytic organisms present in environmental sources, and occurs more commonly among workers engaged in manual labor within rural areas. Mycetomas, more so than the other subcutaneous mycoses, is deeply rooted in communities of low socioeconomic status. 

You may be wondering what the difference is between them. In reality, they are very similar. The need to differentiate them is mostly for management purposes, because treatment is very different. In some textbooks, the appearance of the expressed grains is described as a distinguishing feature, but in practicality this can be hard to do clinically. There are, however, other key differences you should be aware of:

Initially, painless nodules appear in the skin (more often in the lower extremities). As the skin is continually exposed to infected soil or water, multiple lesions can appear. Over the course of months to years, these lesions enlarge, fistulize, and express pus and “grains” forming a mass-like structure. As this “mass” enlarges over time, it can involve the deeper tissues, including the bone! Remember that mycetomas are defined by three hallmark features: i) sinus tracts; ii) grain discharge; iii) painless subcutaneous swelling/masses. Look for the three to make a clinical diagnosis.

For a representative picture of a mycetoma, suggest referencing the CDC website: Clinical Overview of Mycetoma | Mycetoma | CDC

1. Ultrasound: with ultrasound you can differentiate actinomycetoma from eumycetoma in non-invasive manner by their morphological features
2. Microscopy and histopathology: examination of grains under the microscope can differentiate between fungal or bacterial forms. 
3. Cultures: important to differentiate between fungi or bacteria! Important for antibiotic and antifungal susceptibilities.
4. (q)PCR: there are several PCRs described which can identify the most common causative agents of mycetoma directly from the mycetoma grain
5. Other imaging (e.g., X-ray, CT, MRI): needed to evaluate extent of the lesion, evaluate for bony involvement and plan for surgical options.

1. Actinomycetoma: antibiotics like trimethoprim-sulfamethoxazole or amoxicillin-clavulanate are common choices (alternatives: dapsone, aminoglycosides), and combinations are frequent. 
   • Duration: treatment is continued for many months until clinical improvement is noted and bone cultures are negative. 
   • Surgery: adjunctive surgery is rarely needed.
2. Eumycetoma: itraconazole is the most commonly used agent (alternatives: voriconazole, posaconazole). 
   • Duration: treatment is often long and median duration is around 12 months.
   • Surgery: always needed. Amputation is, sometimes, the only way to achieve eradication. 

Cure rates of actinomycetoma can be high (up to 90%), whereas cure rates of eumycetomas are ≤30% at best, leading to high recurrence and often need for amputation.