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Table 6.2. Differential diagnosis between Nocardia, Actinomadura pelletieri, and Actinomadura madurae

Nocardia

(a) Marked soft tissue involvement
(b) Exuberant periosteal reaction
(c) Lace-type periosteum with multiple holes 4-6 mm in size
(d) Multiple bones involved in proximity
(e) Can spread up to leg from the foot
(f) Systemic involvement (pulmonary common)
(g) Multiple sinuses
(h) Mimics tuberculosis but produces more periostitis No sequestra seen

Actinomadura pelletieri

(a) Marked periosteal new bone formation
(b) "Holes" 2-4 mm in size
(c) Granules are red and very small
(d) Aggressiveness and spread not as marked as with Nocardia
(e) Sesamoids affected
(f) Multiple bones involved
(g) Joints affected: joints may ankylose

Actinomadura madurae

(a) Soft tissue involvement. Bone involvement
(b) Moderate periosteal new bone formation: spicules, sun-ray and parallel periosteal reaction
(c) Notching of bone, with constriction and moulding
(d) "Holes" 5-8 mm in size
(e) Large white granules
(f) Osteoblastic and osteoclastic activity present
(g) Sesamoids affected
(h) Splaying and displacement of metacarpal and metatarsal heads

 

Geographic Distribution

Localized mycotic infections are fairly common in much of the Indian subcontinent, throughout Africa (particularly south of the Sahara), and in southern Arabia, South America, and Mexico. While occurring most frequently in the geographic zone between 15 °S and 30 °N, mycetomas are quite common in Japan and numerous cases have been reported from the southern United States. Is is difficult to link the infection to any specific climate or rainfall, but the highest incidence of mycetoma is probably in the Sudan, where over 1200 patients with mycetoma were seen during two and a half years and it was thought that 300-400 new cases developed every year. There may be even more on the Indian subcontinent, because many cases are probably not reported. Another country with a high prevalence is Mexico.

Epidemiology and Pathology

Madura foot is common in people who work in the fields and have either poor or no protection for their feet (Fig. 6.19). It has been particularly linked to minor penetrating wounds caused by thorns or splinters (cf. Fig. 6.20 E, F), and such wounds probably account for many of the other limb mycetomas. It is endemic where thorny acacia trees are common. Whether the organisms are in the soil or growing on the acacia thorns is not decided, but thorns have been found deep within mycetomas (including one in the brain of a child). Those who carry baskets of vegetables or wood on their shoulders or head are likely to get mycotic infections in those sites. It is certain that the true incidence of mycetoma is under-recorded, because in many tropical countries patients with mycetomas are seen so frequently that this tpye of infection causes little comment. Because patients do not suffer much pain or disability in the early stages, they are late in reporting to hospital.

The causative organisms of mycetoma form clusters of grains at the center of the lesion, surrounded by a rim of eosinophilic material (Splendore-Hoeppli) which is in turn surrounded by an abscess and granulomatous reaction. Around the grains will be neutrophils and in the older infections, the fungal grains may degenerate and there will be multinucleated giant cells and epithelioid cells. The perimeter is granulation tissue containing lymphocytes, plasma cells, and histocytes. The histopathological changes are similar regardless of the causal organism (Fig. 6.20 D). The fistulae and sinus tracts start in the skin surface, with sinuses opening from nodular bumps on the dorsal and plantar aspects of the foot (or wherever the mycetoma may be situated). The sinuses discharge fungal grains which can be recognized clinically, and clearly seen when pressed between two glass slides.

There is great geographic variation in the etiology of mycetoma. The most frequent organisms are Madurella mycetomi, Madurella grisea, Pseudallescheria boydii, Leptosphaeria senegalensis, Streptomyces somaliensis, Actinomadura madurae, Actinomadura pelletieri, and Nocardia brasiliensis. Other organisms are very occasionally responsible but it may be impossible to recognize them.

There is some anatomical variation in the frequency with which the fungi cause infection, for example in the Sudan M. mycetoma accounts for the majority of infections of the feet, but S. somaliensis is the likely cause of mycetomas around the head and neck. Considering the number of children watching cattle, fetching firewood and playing in soil in which these organisms are frequently found, it is surprising that mycetomas are relatively infrequent in children and females.

 

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