Monitoring in established RA: Role of imaging and soluble biomarkers.

Rheumatoid arthritis (RA) disease activity often remains difficult to define and to quantify. As a result, numerous techniques to estimate clinical activity have been developed and are in clinical use. Therefore, more objective biomarkers for early detection and accurate measurement and quantification of the disease burden are desired for clinical use and investigative studies. Several imaging and soluble biomarkers have been studied in the disease including conventional radiography, ultrasound, magnetic resonance imaging (MRI), and serum biomarker assays. While these tools are available to physicians in many settings, their role in routine clinical care remains unclear. The goals of this review are to outline the current state of the literature regarding each of these objective tools, assess their strengths and weaknesses, and clarify the knowledge gaps to be filled before these techniques may be more widely used.