Fig. 6.19. A Agricultural laborers who work without adequate foot protection are the most likely to suffer from a "madura foot", but the clinical presentation is very similar in different countries and with different fungi. B,C The swollen foot and ankle of an African from Zimbabwe with multiple discharging sinuses. His main complaint was that it had become a nuisance! D, E A similar chronic infection is a 35-year-old African from Tanzania. The large ulcer on the sole of his foot caused very little discomfort. F In this Indian patient the ankle is more affected than the foot, but the nodular, grained discharging sinuses are typical of a mycetoma.

Imaging Diagnosis

The initial well-circumscribed soft tissue nodule can be demonstrated by ultrasonography (or radiographs or MRI) for a long time before any other abnormality develops. An embedded foreign body should be sought. In the foot there will eventually be multifocal osteomyelitis beneath the soft tissue swelling, affecting many of the small bones (Fig. 6.21). A moth-eaten appearance develops, with lucent defects of variable size, ranging in diameter from 3 to 8 mm. Unlike most cases of tuberculosis, there will be abundant periosteal reaction. The periosteum does not form a barrier to the fungi or actinomycetes, which produce multiple lytic defects in the periosteum, allowing the purulent discharge of colonies from within the cancellous bone. Because there is no tension within the periosteum, the blood supply to the bone ist not interrupted and there is no sequestrum (see Fig. 6.18 C-E). Ultrasonography and MRI can show the subcutaneous abscesses beneath the nodules, from which sinuses discharge.

The joint spaces are preserved until late in the disease (Fig. 6.22), but the sesamoid bones can be affected. Eventually the intraosseous microabscesses coalesce and communicate internally, and the articular cartilage becomes involved. In the later stages, due to either fungal arthritis or secondary infection, bony fusion develops across the joint. If the intraosseous or subcutaneous abscesses communicate with sinuses to the skin, air may be found in the smooth, cyst-like cavities from which the contents have been discharged. Arteriography shows that the granulomatous areas are hypervascular. They "blush" because of surrounding granulomatous tissue. The vascularity of these pseudotumors often seems to extend into the bones with a desmoplastic reaction.

As shown in Table 6.3, radiologically there is a difference between the eumycetomas and the actinomycetomas. Another significant difference is that some fungal infections involve only the foot (or other local area), whereas other spread up the leg or limb (Fig. 6.23). This provides an early screening method in the identification of the organisms.

Radionuclide scans are useful because they will demonstrate sites of infection which have not been recognized clinically or radiographically. Unfortunately, as is often the case with radiographs (Fig. 6.24), they do not help in the recognition of the causal fungus.

If treatment is succesful, the extent of healing may be remarkable. The periosteal reaction coalesces, forming a "melting snow" appearance on the cortex of the small bones. Spontaneous remission is not recorded, but in some patients there may be temporary improvement.

Kaposi sarcoma must be considered in the differential diagnosis, especially in those areas where Kaposi sarcoma is common, even in patients who are HIV-negative. In Kaposi sarcoma, one foot may by be swollen, with multiple soft tissue nodules and destruction of the bones of the foot (or insome patients, the hand), and it may be difficult to distinguish between Kaposi sarcoma and mycetoma (cf. Fig. 6.24 A). In most patients with Kaposi sarcoma, further spread of the nodules up the leg, or onto the other leg (or arm), occurs quite rapidly, whereas the progress of mycetoma is slow and extremely chronic. Surgical excision has been advised in some cases of mycetoma to remove the "mass" of infected tissue and, in the end, even amputation may be necessary.