Derm Dx: An immigrant with nodules, abscesses and fistulae draining clear viscous exudate on the left foot and ankle

Mycetoma is a rare, often painless, chronic localized subcutaneous infection that occurs when bacteria or fungi enter the body, usually through sites of local trauma such as a cut on the hand or a splinter in the foot. Endemic in...

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Mycetoma is a rare, often painless, chronic localized subcutaneous infection that occurs when bacteria or fungi enter the body, usually through sites of local trauma such as a cut on the hand or a splinter in the foot.

Endemic in Africa, India and Mexico, and in parts of Central and South America, mycetoma is rare in the United States, but cases are becoming more common with increased international travel. Farmers, shepherds, Bedouins, nomads and people living in rural areas in endemic countries are most likely to become infected.

Infection causes a granulomatous inflammatory response in the deep dermis and subcutaneous tissue that can extend to the underlying bone. The foot, lower leg and dorsal aspect of the forefoot are the most commonly affected areas, followed by the hand; however, lesions can also occur on the face, neck, chest and upper back.

Bacterial mycetoma is most commonly caused by microaerophilic actinomycetes and termed actinomycetoma, whereas mycetoma caused by true fungi is called eumycetoma. As many as 20 different types of bacteria or fungi can cause mycetomas, but actinomycetoma accounts for about 60% of all mycetomas worldwide.

Actinomadura madurae, Actinomadura pelletieri, Streptomyces somaliensis and Nocardia species are the organisms most often responsible for actinomycetoma; whereas eumycetoma is primarily caused by Pseudallescheria boydii, the organims most common in U.S. cases.

The earliest sign of mycetoma is a painless subcutaneous swelling, sometimes with a history of penetrating injury at the sight of the swelling.

A painless swelling nodule may occur years later, which progresses over the course of years to skin manifestations characterized by induration, abscess formation, skin rupture, fistulae and sinus tract formation. These can form extensive suppurative plaques measuring up to 20 cm and diameter and can spread to contiguous parts of the body.

About 20% of patients experience pain from secondary bacterial or bone infection. Patients rarely experience constitutional symptoms.

Diagnosis

Along with clinical history, epidemiologic consideration and general pathologic features, several laboratory and imaging procedures are necessary to diagnose patients with mycetoma.

Deep wedge shaped surgical biopsy or fine needle aspiration and microbiological cultures are necessary to confirm the diagnosis and distinguish between mycetoma grains.

With hematoxylin-easin stain actinomycetoma appears homogenously easinophilic, whereas eumycetoma has a brownish color. On May-Grünwald-Giemsa stain, actinomycetoma is blue in the center with a pink filament in the periphery, whereas eumycetomas are black with a green tinge.

Tissue gram stains are also useful to detect the fine, gram-positive branching filaments present in the actinomycetoma grain. For eumycetoma, gomori methenamine-silver stain or periodic acid-Schiff stain can demonstrate the characteristic large hyphae.

If bone involvement is suspected clinicians should perform bone radiography, MRI, ultrasonography or computed tomography scanning.

Treatment

Individualized therapy based on the causative agent is necessary and clinicians that are unfamiliar with mycetoma should consult with an infectious disease or tropical medicine specialist. Treatment involves antibiotics and antifungals along with limited surgery for localized mycetoma lesions that can be excised without causing residual disability.

Antibiotic therapy is successful in about 90% of patients with actinomycetoma that receive treatment early in the course of the disease, and generally consists of some combination of trimethoprim-sulfamethoxazole, dapsone and streptomycin sulfate in five week cycles, usually repeated once or twice.

Other antibiotics that have been used to treat actinomycetoma include doxycycline, amikacin and rifampin. Imipenem and cilastatin have been used to treat multiple organism infections in which other agents are contraindicated due to the potential for toxicity, and gentamicin has been used to provide coverage against gram-negative bacteria.

Eumycetoma is considered a more chronic disease, with successful antifungal therapy in about 40% of cases. Patients usually only respond partially to antifungal medication, therefore surgical therapy is preferred for treating localized lesions.

The type of antifungal prescribed will depend on the species causing the infection and can include ketoconazole, itraconazole, amphotericin B and voriconazole.

Prognosis is best for mycetomas that are promptly diagnosed and treated, as patients with advanced stages often have limited treatment response. If a chronic infection is neglected, amputation may be necessary.

References

1. Anía BJ. Mycetoma. Medscape Reference. 2008.

2. Freedberg IM, Isin AZ, Wolff K, et al. Fitzpatrick’s Dermatology in General Medicine (5^th ed.). 1999. New York: McGraw-Hill.

3. Welsh O. Dermatologic manifestations of mycetoma. Medscape Reference. 2009.