What are the advantages of ultrasound imaging in rheumatoid arthritis diagnosis?
A traditional method of monitoring the joint disease of patients with rheumatoid arthritis is X-rays, whereby images are produced by exposing photographic film (radiographs). This technique has proven useful for doctors to follow the course of joint destruction. The early development of discrete bony destruction (erosions) is associated with more severe rheumatoid disease. While standard X-ray radiographs contribute substantially to the clinical evaluation of rheumatoid arthritis, they do lack some sensitivity early in the course of disease. This means that substantial joint destruction must happen before changes on the standard X-ray test become apparent.
Modern treatment for rheumatoid arthritis is frequently directed at early disease. Accordingly, there efforts to establish methods for early diagnosis of the disease have increased. Several radiographic imaging modalities have been explored, including magnetic resonance imaging (MRI) and ultrasonography. MRI scanning has been found to be sensitive as an indicator of early rheumatoid joint destruction, but it is very expensive and not widely available. Ultrasonography is an attractive method of imaging because of its low cost, absence of harmful radiation, and rapidity of imaging. Recent advances in ultrasound image technology have allowed the development of sonographic equipment for imaging inflamed joints in patients with rheumatoid arthritis.
Is ultrasound better than X-ray technology for diagnosing rheumatoid arthritis?
In a study published in Arthritis & Rheumatism, ultrasound imaging was compared with standard X-ray imaging and shown to be superior at detecting bone erosions early in the course of rheumatoid arthritis.
In this study, 100 patients with rheumatoid arthritis underwent ultrasound and X-ray imaging of their hands. Twenty control patients were included in the ultrasound (but not X-ray) analysis for comparison. In the group of 100 RA patients, 127 abnormalities were detected in 56 patients by ultrasound, compared with 32 abnormalities in 17 patients detected by X-ray analysis. When patients with early rheumatoid arthritis were analyzed, 6.5-fold more abnormalities were detected by ultrasonography than by X-ray films. There were erosions detected by X-ray that were missed by ultrasound; the correlation between erosions seen by X-ray and those seen by ultrasound was 86%.
From these results, the authors conclude that ultrasound is a reliable technique with greater sensitivity than standard X-ray radiography. They note that the ultrasound technique is influenced and limited by technical performance, requiring appropriate use of the sonographic equipment. (I would add that ultrasound technique and interpretation are both delicate matters. And for this test to prove out useful, many more studies and standardizations will be required.) Other limitations of this study include the technique used for analysis (only one X-ray view was obtained) and patient selection (patients with severe deformities were excluded).
Overall, these results hold out the potential for a rapid, safe, and sensitive alternative to traditional X-ray analysis of joints in RA patients. We await further studies that will be necessary to correlate ultrasound findings with clinical outcomes in rheumatoid arthritis such as disease progression, joint destruction, and response to therapy. For now, X-ray testing remains the standard monitoring test for joint destruction.