Fig. 6.41 A-E. Histoplasmosis duboisii should always be considered (where geographically likely) when there are multiple irregular areas of bone destruction, often with suprisingly little periosteal reaction. A A large lytic lesion in the upper end of the humerus with minimal periosteal elevation. There are multiple areas of bone destruction in the scapula, some showing reactive sclerosis. B Multiple quite large destructive foci in the upper end of the humerus, with disruption of the humeral head. There is soft tissue swelling. C Another patient with multiple lytic areas in the lower half of the humerus, destruction of the elbow joint, and further foci in the upper end of the radius and ulna. The humerus shows more periosteal reaction than is usual. D The shoulder joint of this patient has been completely destroyed and there are multiple lytic foci in the humerus and the remains of the scapula. There are also many foci in the ribs. E A different patient with multiple lytic areas in many of the ribs on both sides. All the patients in Fig. 6.40 and Fig. 6.41 came from West Africa. (Courtesy of the late Professor W P Cockshott)

Imaging Diagnosis

Histoplasma capsulatum var. duboisii infections usually arise in the metaphyses of the long bones, the small bones of the hand, and the flat bones. The earliest lesion is a small lytic area, as occurs in multiple myeloma, skeletal metastases, or, in some patients, tuberculosis. These lesions are often quite diffuse, and in small bones there may be a latticelike area. The center of these bone infections becomes necrotic and can drain into the soft tissues, forming a subcutaneous abscess which may persist deeply or connect with the skin. Although there is some periosteal reaction, this is often made worse by secondary pyogenic infection acquired through a draining sinus.

Infection of bone can be widespread and dramatic, involving the whole length of long bones. Paraplegia from vertebral involvement has been reported, with the discs usually remaining intact (as occurs in other infections, e. g., actinomycosis and coccidioidomycosis). Paraspinal abscesses may develop and drain through sinuses.

In the disseminated pattern, the pulmonary lesions are difficult to distinguish from tuberculosis or from histoplasmosis capsulati. In one patient diffuse miliary nodules were observed radiographically, and at autopsy granulomatous nodules were found throughout both lungs and within enlarged and necrotizing lymph nodes. This pattern has been seen in other patients, and has responded to treatment.
Direct spread to other systems is uncommon.

The imaging diagnosis of histoplasmosis duboisii is in many ways easier than that of other fungal or pyogenic bone infections, though distinction from neoplasm may be difficult (Fig. 6.40). The extent of the bone destruction and the multiple bones involved as the disease progresses result in a characteristic pattern (Fig. 6.41).