FDG-PET/CT in the assessment of rheumatoid arthritis disease activity, complications, and treatment response

Introduction: 1. Discuss the utility of ¹⁸F-fluorodeoxyglucose (FDG)-PET/CT to evaluate the severity of rheumatoid arthritis. 2. Assess the ability of ¹⁸F-FDG-PET to identify complications of rheumatoid arthritis. 3. Determine the utility of ¹⁸F-FDG-PET in assessing the response of rheumatoid arthritis patients to therapeutic interventions.

Methods: Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disorder characterized by pannus formation, swollen joints and stiffness. Conventionally, magnetic resonance imaging (MRI), rather than computer tomography (CT), has been used to assess RA, as it allows for the earlier identification of damage to cartilage and soft tissue. However, CT and MRI are unable to show the molecular activities which determine these structural changes. Conversely, FDG-PET enables sensitive detection of synovial inflammation, even in asymptomatic stages. FDG, a radiotracer that serves as a glucose analog, accumulates in the inflammatory cells. Thus, FDG-PET is a powerful tool that can allow for earlier diagnosis and intervention in RA.

Results: Joint involvement in RA has been successfully identified by FDG-PET. FDG uptake is higher in joints affected by RA and has been found to be correlated with markers of systemic inflammation. Increased FDG has been associated with pannus formation, consisting of fibrovascular inflammatory tissue. Pannus formation is directly correlated to cartilage and bone destructive characteristics of RA. Progression of disease in the atlanto-axial joint in the cervical region has also been successfully identified by FDG in asymptomatic patients. FDG-PET has also been found to have utility in the detection of extra-articular manifestations, such as subcutaneous nodules and interstitial lung disease, allowing for more precise diagnosis and management. FDG-PET is also capable of assessing whole-body response to treatment through quantitative assessment. In patients treated with anti-TNF therapy, FDG-PET can categorize responders and non-responders earlier than other methods, thereby stopping ineffective therapy in a timely manner. Quantitative information from PET can also be combined with morphological details from MRI for the assessment of articular structures and soft tissues. Moreover, RA patients are known to have higher incidence of atherosclerosis and an increased cardiovascular morbidity and mortality. Several studies have highlighted the role of FDG-PET in identifying the existing inflammation in the plaques within the arterial wall. FDG-PET offers an opportunity for early detection of atherosclerosis while the disease is still treatable. The use of a total-body PET/CT also has potential to better reflect and monitor the overall disease activity of RA including the assessment of atherosclerosis.

Conclusions: FDG-PET is a useful tool in the early identification of disease and associated symptoms in RA patients. It also has the potential to monitor treatment response to determine the appropriate regimen for patients, thereby improving patient outcomes.