As the vast majority of such cases are noted in the feet, and as such cases are chiefly in those who work barefooted, it seems reasonable to consider that the fungi are introduced on some puncturing object and the external wound having healed development goes on in the deeper structures.
Pathology
In more than 75% of cases of mycetoma the foot is the only part infected. More rarely there is involvement of hands, knees and buttocks.
The affected part shows nodules on the external surface which connect with the granulomatous lesions of the interior of the foot by sinuses. In advanced cases there may be a network of sinuses and cyst-like dilatations which are filled with a viscid fluid packed with the small fish-roe granules in the white variety or the gunpowder grains of the black mycetoma. The bony structures of the foot may undergo disintegration as well as muscular and areolar tissue so that on cutting into such a foot there is nothing normal remaining—simply a cheesy mass.
In the early granulomatous areas are found the actinomyces-like granules surrounded by an area of mononuclear and polymorphonuclear infiltration. Giant cells are occasionally found. There is an inflammatory oedema. Externally we have connective tissue cells and a fibrous wall. The blood vessels show endothelial proliferation and thrombosis.
Symptomatology
The disease usually begins in the sole of the foot with the formation of firm swellings about ½ inch in diameter. The cases are rarely seen at this stage, the natives waiting before seeking medical advice until the nodule has softened and begun to discharge the viscid fluid with the various-colored granules floating in it. As stated before, the soft, yellowish-white, fish-roe-like granules are most commonly observed, the more friable, hard, gunpowder-like grains less so. The nodules continue to form and to break down until the foot has become greatly enlarged, the under surface bulging out in a convex mass with the toes and heels appearing as if raised up. The dorsal surface is also puffed up and studded with broken down nodules, and the sides well rounded. There is no increase in the length of the foot. This swollen distorted foot is borne on a thin peg-like leg which makes the size of the foot more striking. Very rarely cases have been reported where the hand or thigh have been involved.
If one probes the discharging sinuses bone may or may not be felt according to the advancement of the degenerative changes. There is rarely pain or bleeding following the probing.
It is more from the onerous burden of carrying around this fungoid mass of a foot, 3 or 4 times the normal size, than pain, that the patient complains of.