Bone loss in rheumatoid arthritis: systemic, periarticular, and focal.

Rheumatoid arthritis is a chronic inflammatory disease that results in generalized bone loss and increased fracture risk. Characteristic radiologic features of rheumatoid arthritis include periarticular osteopenia and marginal erosions. An emerging literature highlights the importance of osteoclasts as mediators of the erosive process, with an impairment of bone formation by inhibition of the Wnt signaling pathway as a cause of lack of repair of erosions. MRI has demonstrated the importance of inflammation in the bone marrow compartment as a cause of periarticular osteopenia. The term osteoimmunology has evolved to highlight the association between cells and cytokines of the immune system and their relationship to bone metabolism in rheumatoid arthritis and other forms of chronic inflammatory arthritis.