Imaging Findings of Chronic Coccidioidomycosis Septic Arthritis and Osteomyelitis of the Shoulder Joint

Coccidioidomycosis is a regional fungal infection, endemic to California and the southwestern United States, with an increasing geographic expansion over the years. When symptomatic, it typically causes pneumonia but occasionally spreads to other organ systems, including bone and joints, leading to destructive complications such as septic arthritis and osteomyelitis. Immunosuppressed patients are at higher risk for dissemination. Typical imaging features of skeletal fungal infection include osseous erosions, joint effusion, and synovitis. Coccidioidomycosis can mimic other conditions, including tuberculous arthritis, inflammatory arthritis, crystal deposition disease, and amyloid arthropathy. Diagnosis often requires tissue sampling and culture. We present a case of a 64-year-old woman with biopsy-proven coccidioidomycosis of the shoulder joint, a rare site for this disease. Imaging shows a widespread, destructive joint-centered process without periosteal reaction. This case highlights the diagnostic challenges posed by osteoarticular fungal infections and the importance of including fungal disease in the differential diagnosis of chronic monoarthritis, particularly in patients from, or with a travel history to, endemic areas.