Imaging in Arthritis

The last few years have witnessed truly unprecedented advances in rheumatology, with the introduction of several new compounds capable of halting the otherwise relentless progression of joint destruction, pain, and functional disability in patients with rheumatoid arthritis (RA). These successes, however, have raised the bar considerably for medical imaging. In the past, the performance demands of rheumatology on imaging were rather minimal. Without effective therapies to halt the progression of erosive joint damage, there simply was little need for detailed information about articular structure. Conventional radiography, although intrinsically limited in the information that it could provide in this regard, was adequate for what was needed at the time. Other modalities, particularly magnetic resonance imaging (MRI), offered greater technical performance, but because rheumatologists were satisfied with radiography, they were not willing to pay more for MRI. Indeed, most rheumatologists used even radiography only sparingly, if at all, relying instead on clinical examination and laboratory measures to manage their patients. This approach was not unreasonable given the circumstances of the time. However, this changed when effective structure modifying treatment became available to clinicians, because it shifted the therapeutic focus from limiting pain and toxicity to actually reducing the progression of structural damage in patients with RA.

This shift in patient management created new demands on imaging both in clinical practice and in clinical research. One important consequence is that it is no longer ethical to withhold effective therapy from patients and, therefore, to conduct placebo-controlled clinical trials. This necessitates that putative new agents be tested against established therapies with known efficacy. Because such studies show slower progression and smaller differences among treatment groups, they take substantially longer and require greater numbers of patients and clinical sites to achieve statistical significance. This adds time and cost to drug development, which slows progress and potentially raises the cost of new therapies that do get approved. Unless more sensitive methods of predicting and monitoring treatment effect are adopted, the financial and practical ramifications of this problem will severely hinder further progress in therapeutics for RA.

Additionally, the availability of effective structure-modifying therapy has stimulated a trend toward early, aggressive treatment prior to the development of joint damage and associated irreversible functional disability. However, predicting which patients will progress is extremely difficult in early RA. Accordingly, there is a need for more sensitive ways of identifying the aggressive phenotype of RA at the time of initial presentation, before the narrow window of opportunity for containing erosive disease closes. Unfortunately, conventional radiography is not well suited for this, particularly in early disease, so rheumatologists must look to more powerful imaging technologies, such as MRI, to provide additional performance. This issue of Seminars in Musculoskeletal Radiology addresses this challenge with four reviews that explore the utility of alternative imaging techniques for evaluating disease progression and treatment effect in RA.

Compared with RA, osteoarthritis (OA) presents considerably less dramatically and progresses more slowly, yet OA can be severely debilitating and is 10 times as prevalent as RA. Moreover, the prevalence of OA and therefore its cost to society are rising rapidly as baby boomers age. Unlike RA, OA has experienced relatively little success in structure-modifying therapy, and currently there are no effective treatments that slow or halt the progression of structural and functional joint deterioration in patients with OA. Surgical solutions do exist, but these focus on end-stage disease or provide only focal cartilage defect repair. No preventative or whole-joint solutions are currently available for patients with early OA. Moreover, the pharmaceutical and biotechnology pipeline of putative new therapies for OA is relatively thin, and only a few clinical trials are currently in progress. Most of the clinical research in this area is epidemiological, aimed at elucidating the structural determinants of clinical outcomes in OA, identifying effective therapeutic strategies for the disease, and validating and characterizing biological markers, including imaging markers, which could be used to measure disease progression and therapeutic response. Several MRI measures of articular cartilage morphology and composition hold great promise in this regard. In this issue we also review the current status of MRI and ultrasound of articular cartilage and point to areas where further innovations may be expected in the future.