Nuclear (scintigraphic) methods and FDG-PET in rheumatoid arthritis and osteoarthritis

Imaging of inflammatory joint diseases remains challenging. The development in recent years of biologic treatments that are highly efficacious as well as expensive has stimulated the research for imaging of inflammation. This has been particularly true for rheumatoid arthritis (RA), which constitutes the most prevalent inflammatory arthritis, affecting 1% of the population. RA is an autoimmune systemic disease characterized by chronic inflammation of the synovium, with a massive leukocyte infiltration, proliferation of the synovial membrane, and neovascularization. The hyperplastic and hypertrophic rheumatoid synovium, termed the pannus, if left untreated gradually erodes the adjacent cartilage and bone, leading to joint degrada- tion and marked disability. Although conventional radiography displays joint space narrowing and bone erosions, the hallmark of rheumatoid disease, it does not allow evaluation of the inflammatory component of the disease but only its end-stage irreversible characteristics. MRI can detect bone erosions earlier than conventional radiography and also allows the study of cartilage, tendons, and ligaments, as well as the synovium, especially after the injection of gadolinium. However, in gadolinium-enhanced MRI the uptake of the contrast agent by the inflamed synovium is also due to hypervascularization and capillary permeability. Ultrasonography is noninvasive, allows the study of many joints in one time frame, and when associated with power Doppler imaging can also give information about synovial vascularization. Although these two imaging modalities are of high value in the clinical assessment of arthritis (as discussed more fully in other chapters), they remain purely morphologic and do not provide information about cell metabolism. In this chapter we review the nuclear medicine techniques available for assessing arthritis, with a particular interest in positron emission tomography (PET).