Mycetoma

What is mycetoma (Madura foot)?

Mycetoma (named because of the tumour-like mass it forms) is a chronic granulomatous disease characterised by localised infection of subcutaneous tissues by actinomycetes or fungi. The inflammatory response can extend to the underlying bone.¹ Mycetoma was described first in the mid-1800s and was initially called Madura foot.²

• The infection can be caused by true fungi (eumycetoma) in 40%, or filamentous bacteria (actinomycetoma) in 60%.³

• Actinomycetoma may be due to Actinomadura madurae, Actinomadura pelletieri, Streptomyces somaliensis, Nocardia spp.

• Eumycetoma is often due to Pseudallescheria boydii (Scedosporium apiospermum), Madurella mycetomatis.

• Infection enters through sites of local trauma - eg, a cut or splinter, causing a granulomatous reaction. Spread occurs through skin facial planes and can involve the bone. It most commonly involves the foot but can involve the hands, back or shoulders.

Mycetoma epidemiology^{4 5}

• The disease is endemic in the tropics and subtropics and is named after the region of India where it was first described in 1842. It occurs in what has been described as 'the mycetoma belt' between the latitudes of 15° South and 30° North and is endemic in arid areas.⁶

• There are a series of case reports from African countries, including Sudan.

• Although currently uncommon in temperate regions, it does occur in the southern USA and cases are found in the homeless and in AIDS sufferers.

• The incidence of mycetoma is likely to rise in temperate regions, due to increases in worldwide travel and, since mycoses are not notifiable, the incidence in the UK is unknown.

• Mycetomas can occur in all ages although are more common between 20-40 years and in the male population.⁵

Risk factors⁵

• Mycetoma typically presents in agricultural workers (hands, shoulders and back - from carrying contaminated vegetation and other burdens), or in individuals who walk barefoot in dry, dusty conditions.

• Minor trauma allows pathogens from the soil to enter the skin.

Mycetoma symptoms

• Following the initial injury, the disease typically follows a slow chronic course over many years with painless swelling and intermittent discharge of pus.

• There may be a deep itching sensation.

• Pain may occur due to secondary bacterial infection or bone invasion.

• After some years, massive swelling of the area occurs, with induration, skin rupture and sinus tract formation. As the infection spreads, old sinuses close and new ones open.

• The exudates are typically granular.

Differential diagnosis

• The main differential diagnoses are chronic bacterial osteomyelitis, tuberculosis, or the early phase of Buruli ulcer.

• Other deep fungal infections such as blastomycosis or coccidiomycosis.

• Leishmaniasis, yaws and syphilis should be considered.
  

Investigations^{2 3}

• Microscopy and culture of exudates and skin biopsy for pathology are necessary to identify the causative organism.

• Serology can be helpful with diagnosis or follow-up care during medical treatment.

• DNA sequencing has been used for identification in difficult cases.

• Plain X-rays are used to assess for evidence of bone involvement.⁷

• CT scan may be more sensitive in the early stages.
  MRI scans can provide a better assessment of the degree of bone and soft tissue involvement, and may be useful in evaluating the differential diagnosis of the swelling.

Mycetoma treatment

Actinomycetomas usually respond better than eumycetomas to medical treatment - the latter often being difficult to treat. Bone involvement complicates clinical management, often leaving surgical amputation as the only treatment option.^{5 8}

• Due to the slow, relatively pain-free progression of the disease, mycetoma is often at an advanced stage when diagnosed.

• Surgical debridement, followed by prolonged appropriate antibiotic therapy for several months is required for actinomycetoma.⁹ Combination therapy with trimethoprim-sulfamethoxazole, dapsone and streptomycin has been used. Rifampin has been used in resistant cases.¹⁰

• Eumycetomas are only partially responsive to antifungal therapy but can be treated by surgery, due to their normally well circumscribed nature. Surgery in combination with azole treatment is the recommended regime for small eumycetoma lesions in the extremities.¹¹ M. mycetomatis may respond to ketoconazole,¹² P. boydii (S. apiospermum) may respond to itraconazole. Other agents of eumycetoma may respond intermittently to itraconazole or amphotericin.³

• The use of traditional herbal medicine is commonly associated with a delay in seeking medical care, resulting in patients presenting with more advanced disease.¹³

Complications

• The disease causes disfigurement but is rarely fatal.

• In advanced cases, deformities or ankylosis may occur.

• Chronic neglected infection may necessitate amputation.

• Immunocompromised patients may develop invasive infection.

• Lymphatic obstruction and fibrosis may cause lymphoedema.

• Complications may result from toxicity due to prolonged antimicrobial or antifungal therapy.

Prognosis

• Actinomycetoma can be cured with the appropriate antibiotic therapy but eumycetoma has a high rate of recurrence and can require amputation.

• A high incidence of secondary bacterial infection in mycetoma lesions has been reported.¹² This can cause increased pain and disability as well as septicaemia, which may be fatal if untreated.