20-40: Mycotic Infections of Bones & Joints

Fungal infections of the skeletal system are usually secondary to a primary infection in another organ, frequently the lungs (see Chapter 36). Although skeletal lesions have a predilection for the cancellous portions of long bones and vertebral bodies, the predominant lesion—a granuloma with varying degrees of necrosis and abscess formation—does not produce a characteristic clinical picture.

Differentiation from other chronic focal infections depends on culture studies of synovial fluid or tissue obtained from the local lesion. Serologic tests provide presumptive support of the diagnosis.

1. CANDIDIASIS

Candidal osteomyelitis most commonly develops in debilitated, malnourished patients undergoing prolonged hospitalization for cancer, neutropenia, trauma, complicated abdominal surgical procedures, or injection drug use. Infected intravenous catheters frequently serve as a hematogenous source. Prosthetic joints can also be infected by Candida.

For susceptible Candida species, fluconazole, 200 mg orally twice daily, is probably as effective as amphotericin B (see Chapter 36).

2. COCCIDIOIDOMYCOSIS

Coccidioidomycosis of bones and joints is usually secondary to primary pulmonary infection. Arthralgia with periarticular swelling, especially in the knees and ankles, occurring as a nonspecific manifestation of systemic coccidioidomycosis, should be distinguished from actual bone or joint infection. Osseous lesions commonly occur in cancellous bone of the vertebrae or near the ends of long bones at tendinous insertions. These lesions are initially osteolytic and thus may mimic metastatic tumor or myeloma.

The precise diagnosis depends on recovery of Coccidioides immitis from the lesion or histologic examination of tissue obtained by open biopsy. Rising titers of complement-fixing antibodies also provide evidence of the disseminated nature of the disease.

Oral azole antifungal agents (fluconazole or ketoconazole at 400 mg daily, or itraconazole 200 mg twice daily) are the treatment of choice for bone and joint coccidioidomycosis. Chronic infection is rarely cured with antifungal agents and may require operative excision of infected bone and soft tissue; amputation may be the only solution for stubbornly progressive infections. Immobilization of joints by plaster casts and avoidance of weight bearing provide benefit. Synovectomy, joint debridement, and arthrodesis are reserved for more advanced joint infections.

3. HISTOPLASMOSIS

Focal skeletal or joint involvement in histoplasmosis is rare and generally represents dissemination from a primary focus in the lungs. Skeletal lesions may be single or multiple and are not characteristic.