Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects the joints, causing them to become painful, swollen and stiff. If untreated, it progresses, seriously debilitating a person’s quality of life. It starts out with inflammation of the synovial membrane (the area between the joint capsule and the joint) and then starts to attack the surrounding cartilage and bone. Consequently, a person may be left with disfigured hands and wrists, which is why early diagnosis is essential.
How is RA diagnosed?
Currently, a series of clinical and laboratory tests must be performed for proper diagnosis. These include but are not limited to testing for rheumatoid factor (RF), anticitrullinated peptide (anti-CCP), erythrocyte sedimentation rate (ESR), and/or serum C-reactive protein (CRP). Also, some sort of imaging is done, usually X-ray, to help the rheumatologist better visualize and evaluate the stage of disease. It has been around for a relatively short time, but ultrasound is making a name for itself in the realm of RA, as an accurate, sensitive tool for finding the faintest signs of the disease that affects up to 1% of the world’s population
What does ultrasound have to offer?
Ever since the 1980’s, ultrasonography has been quickly evolving as a powerful tool for rheumatology. Grey scale ultrasound is highly sensitive to changes in the thickness of tissues, but it lacks the depth of vision to show the earliest markers of inflammation.
Bone erosions (destruction) are characteristic of advanced RA. Normally, an X=ray examination is performed to judge the stage of progression. A big disadvantage to going the X-ray route is that it’s not nearly as sensitive as ultrasound. This means X-ray will only catch RA in its later stages, when there are significant bone erosions. Of course, as any other method, ultrasound has some limitations, as it is user-dependent which special training and standardization will sort out.
Power Doppler has the ability to highlight the smallest increase in blood flow in the inflamed joint, which is characteristic of disease activity. It can identify subclinical manifestations and determine if the disease is in remission or is slowly rearing its head. There is also extensive evidence that power Doppler correlates well with laboratory/clinical findings, MRI and histopathological data. Treatment response is incredibly important in rheumatology because symptoms tend to gradually go away over the course of days or weeks. Power Doppler can help physicians determine patients that are resistant or poorly responding to standard therapy.
Power Doppler grading of synovitis:
Grade 0: being with no signal visualized
Grade 1: having one single or several vessels visualized
Grade 2: less than 50% of the region of interest having signal
Grade 3: being more than 50% of the region of interest having signal
Pulse-inversion harmonic imaging (PIHI) is a technique that uses microbubble contrast material, like Sonovue (sulfur hexafluoride, Bracco), to enhance images with superior delineation. Microbubbles have unique properties that make their use ideal for detecting flow in small blood vessels. PIHI is unique because it uses two pulses, one standard pulse and the other, an inverted pulse of the original. As these pulses pass through the body and are combined, the result is an automatically filtered image. According to researchers, PIHI is more sensitive than power Doppler for detecting minute changes in synovial vascularization. Using this method in routine practice may not be beneficial over power Doppler, but contrast-enhanced ultrasound in general can detect small slow-moving blood vessels when standard power Doppler turns up nothing.
Combining diagnostics and therapy
Although at one point in time controversial, the use of ultrasound therapy for RA patients has been proven effective. Ultrasound waves help improve grip strength and in some cases increase wrist flexibility, decrease morning stiffness and reduce inflammation in joints.
Another advantage ultrasound brings to the table is a considerable bump in accuracy for ultrasound-guided joint injections and aspirations.
As 2D ultrasound is very operator-dependent, introducing 3D ultrasound can bridge the gap to eventually have standardized scans. 3D volumetric data can be manipulated at a later date and viewed on multiple planes.
4D transducers will give doctors the opportunity to visualize afflicted joints in real-time. Not a lot of these 4D transducers are on the market , but developing linear transducers for small parts and superficial tissue can simplify acquisition of volumetric data because all the measurements are done automatically. If medical equipment manufacturers develop these technologies along with accompanying software, we could be one step closer to a fully quantitative measurement of disease activity, which would improve quality of life for patients.
Reaching new heights
Rheumatoid arthritis is a mysterious autoimmune disease that can cause serious damage to a patient’s joints as well as their psychological well-being. Until recently, ultrasound was not considered a viable option for imaging arthritic joints, but it has quickly caught up. The reason it has become so popular is the fact that it’s affordable, accurate and it is now considered a highly sensitive tool for diagnosing, monitoring and treating RA. With the advent of new technologies like 4D probes, we will see a revolution in standardization which will give way to overall improvement of diagnosing and treating this crippling disease.
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