Rheumatoid arthritis, which affects approximately 2.9 million people in Europe, can be difficult to differentiate from other forms of arthritis. Without an early diagnosis, however, it is impossible to assess the true effect of promising early intervention strategies. Could an alternative diagnostic imaging strategy be the answer?
Speakers at a special focus session addressed the value of ultrasound and MRI in diagnosing RA and monitoring the effects of therapy. Both of these modalities are used in the research setting to characterize inflammatory arthropathies, detect changes in disease progression, and/or identify responses to treatment before such changes become clinically apparent.
Routine implementation is now just a matter of time, according to the session's chair, Dr. Andrew Grainger, a musculoskeletal radiologist at the Leeds Teaching Hospitals NHS Trust in the U.K.
Studies have shown that ultrasound can demonstrate the hallmarks of inflammatory arthropathy with good sensitivity and specificity, said Dr. Philip O'Connor, also a musculoskeletal radiologist at the Leeds Teaching Hospitals. A definitive diagnosis of RA is typically made when these imaging findings are combined with clinical signs, patient history, and biochemical information.
"I have been using ultrasound in rheumatoid arthritis since 1996," he said. "It adds a lot to the clinical examination and to clinical management and decision making in these patients. If you had a close relative with early inflammatory arthritis, you would want them to have an ultrasound scan to determine what was going on inside those joints."
Contrast-enhanced MRI has the potential to speed up definitive diagnoses of RA, according to Dr. Christian Glaser, a radiologist at the University Hospital of Munich-Grosshadern in Germany. Patients attending the Munich hospital are already referred for an MR examination if doctors suspect RA but the clinical signs are unclear.
The earliest indication of RA is the appearance of synovitis. This finding is also seen in osteoarthritis, though it is much less common and severe. Contrast-enhanced MRI can detect synovitis as early as two months after the onset of symptoms.
Another early stage in disease progress is inflammatory invasion of the bone marrow, or bone marrow edema pattern (BMEP). This appears as regions of "fluffy" hyperintensity in the affected areas of bone, Glaser said. BMEP typically precedes structural changes to the bone known as erosions. These bitelike defects in the cortical bone indicate the onset of irreversible damage.
"These bony erosions are very slow to heal, if they heal at all. If you have many erosions and cartilage defects in the bone, you are likely to proceed to joint destruction," he said.
Dynamic contrast-enhanced MRI can be especially helpful. Studies suggest that a rapid rise in enhancement in affected joints, shortly after contrast is administered, can be taken to indicate the presence of an active inflammatory process. A steadier increase in enhancement over a longer period of time is suggestive of chronic disease or a reduction in inflammatory activity.
Scoring criteria based on MRI observations are being developed so that disease progression and therapy response can be assessed more objectively. Measurements may include thickness of the inflamed synovium, brightness of synovial contrast enhancement, and area affected by BMEP.
Glaser regards MRI and ultrasound as complementary tools rather than rivals for the diagnosis and follow-up of RA. Ultrasound has unparalleled spatial resolution when applied to small joints, though its value depends on the experience of the user. MRI results are far less dependent on operator expertise.
"It would be very practical for a doctor diagnosing or treating a rheumatology patient to use ultrasound to examine a specific small joint, perhaps in a finger or toe, to assess a pattern of destruction or inflammatory activity," he said. "With MRI, you can get a complete overview of the hand, wrist, or ankle area, and you can visualize regions deeper in the body not readily accessible to ultrasound."
O'Connor agrees that ultrasound and MRI can work well together. Software packages are now available that allow 3D MRI data sets to be registered to an ultrasound examination in real-time. As the ultrasound probe is moved across the patient, the MR images shown will reorientate to the same position. Findings from each modality can be correlated with one another and new techniques validated.
Ultrasound is likely to make the transition from research tool to clinical practice more easily than MRI, O'Connor said. The modality is cheaper, and examinations are more comfortable for patients. Concerns over reproducibility may be eased by the introduction of 4D techniques in which blocks of data are acquired. Ultrasound remains a hands-on modality, however, and advances in technology will not obviate the need for good training.
"The problem is that there is no real training program in radiology built around inflammatory arthritis scanning with ultrasound," he said. "It is my belief that this will become a rheumatological procedure. Rheumatologists are developing their own training schemes and courses. I don't think radiologists have the time or staffing to offer this service."
