Mycetoma: causes, symptoms, diagnosis, and treatment

Mycetoma is a chronic, progressive, local infectious disease caused by various fungi or bacteria. The foot, distal upper extremities, and back can be involved. Clinical symptoms include swelling and sinus formation.


Causes

Mycetoma is a chronic granuloma with pus filled sinus tracts. The pathogens adhere to the soil or plants, and can invade the human body through skin trauma. Particularly, the pathogens often invade the feet of individuals who walk barefoot. The pathogens are usually harmless to humans, and only invade the human body when the hosts have reduced immunity, so they are conditioned pathogens.

The pathogens may be Nocardia asteroides or Nocardia brasiliensis, which can cause nocardial mycetoma. In some areas, the pathogens are Streptomyces somaliensis, Actinomadura pelletieri, or Actinomadura madurae, and mycetoma caused by these pathogens are collectively called actinomycetoma or actinomycotic mycetoma.

Mycetoma can also be caused by fungi with septate hyphae, such as Madurella mycetomatis, which are collectively termed eumycetoma or eumycotic mycetoma.

The clinical manifestations of actinomycotic mycetoma and eumycotic mycetoma are the same, but the pathogens vary in different regions. In India, Africa, and South America, maduromycosis caused by fungi is more common, and occurs predominantly on the feet of barefoot travelers, which is termed madura foot, usually on unilateral feet.


Signs and Symptoms

The initial lesions may be papules, fixed subcutaneous nodules, vesicles or subcutaneous abscesses with indurated base, forming fistulas communicating with the skin surface after rupture. Fibrosis often occurs in or around early lesions. If there is no acute suppurative bacterial infection, only mild tenderness or no tenderness is present.

 

Figure 1 mycetoma

In the course of months or even years, the disease progresses chronically, gradually spreading to adjacent tissues, causing damage to adjacent muscles, tendons, fascia, and bones. There is neither systemic disseminated infection nor signs and symptoms of systemic infection. Eventually, the muscles of the limbs gradually decrease, the limbs deform, the tissues are destroyed, and the affected limbs cannot move. In the late stage of infection, the involved limb is abnormally swollen and deformed, and cupular cystic masses are locally formed. Multiple interconnected sinus tracts and fistulas are formed, and thick or serosanguineous discharges containing characteristic white or black particles are present.


Histopathology

The histologic changes are mainly non-specific chronic granuloma with abscesses and fistulas, followed by fibrosis.

Pus contains small, white, yellow, red, or black, 0.2 - 3mm in size, usually lobulated particles, probably with Splendore-Hoeppli phenomenon. The particles are in the center of the abscess and are surrounded by neutrophils, lymphocytes, foreign body giant cells, and plasma cells infiltration. Thick or thin hyphae can be seen in the particles. Actinomycetic particles can be seen in Gram stain, while fungal particles can be found in PAS or GMS stain.


Diagnosis

On the basis of typical clinical presentations and different colored particles in the pus, the disease can be diagnosed.


Treatment

Actinomycotic mycetoma can be treated effectively with antibiotics such as streptomycin in combination with sulfonamides. After recovery, it is necessary to continue treatment for 3 - 4 months to prevent recurrence. Surgical treatment can be considered if necessary.

The treatment of eumycotic mycetoma is extremely difficult. Early lesions should be completely and extensively excised, because the extent and depth of skin lesions are often more severe than observed on the surface. In the late stage, amputation may be the only option. Itraconazole and fluconazole can be administered for at least 3 months.

Local lesions of mycetoma can be treated with local injection of amphotericin B solution.

Nocardial mycetoma can be treated with penicillin G in combination with compound sulfamethoxazole.