What is the role of ultrasonography of the hands in the workup of rheumatoid arthritis (RA)?

Updated: Mar 28, 2019
  • Author: Ian Y Y Tsou, MBBS, FRCR; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Answer

High-resolution sonography with a high-frequency probe is used for evaluation of the small joints in RA; see the image below. Joint effusion is hypoechoic, while the hypertrophic synovium is more echogenic. Rheumatoid nodules are seen as fluid-filled round cavities with sharp borders. Bone erosions may be seen as irregularities in the hyperechoic cortex. [23, 25]

Illustration of the scanning technique. Photograph Illustration of the scanning technique. Photograph depicts the typical scanning technique with application of the Entos Probe to the volar (flexor) aspect of the third metacarpophalangeal joint. The technique allows visualization of the joint surfaces, flexor tendon, and synovial sheaths in patients with rheumatoid arthritis.

Complications of RA, such as tenosynovitis and tendon rupture, can also be visualized by using ultrasonography. This is most useful in the MCP and IP joints. The carpal bones and the carpometacarpal joints are not visualized as well because of their irregular configuration and deeper location. [27, 28, 29, 30, 31, 32]

Sonography has been applied to the assessment of RA with the goal of improving on the current standard of conventional radiography. Ultrasonography, especially when augmented by amplitude color Doppler (ACD) imaging, has also provided clinically useful information in the assessment of RA. Originally, ACD or power Doppler scanning was developed as an improvement to existing vascular sonographic imaging techniques to delineate stenoses by imaging blood flowing in vessel lumina by virtue of higher sensitivity to flow and lack of directional dependence. [33]

ACD imaging has been applied to RA with the goal of evaluating the manifestation of hyperemia in the inflammatory joint tissues at the symptomatic sites of disease. Synovial hyperemia is a fundamental pathophysiologic feature of RA. Most likely, synovial hyperemia is the principal factor underlying the hallmark x-ray observation of periarticular demineralization on radiographs of patients with RA, and it is believed to occur in proportion to joint-destructive disease activity. Hyperemia in the tendon sheath is common as well. See the images below.

Amplitude color Doppler sonogram in a patient with Amplitude color Doppler sonogram in a patient with active rheumatoid arthritis. Dorsal (extensor) surface of the second metacarpophalangeal joint is imaged. Intense-amplitude Doppler color flow signal demarcates the inflamed synovium (ie, joint pannus) resulting from severe hyperemia. Solid arrows indicate the extensor tendon sheath and dorsal and volar margins. Straight open arrow indicates the synovium of the joint overlying the proximal phalanx of the second digit. Curved open arrow indicates the inflamed synovium overlying the metacarpal. The asterisk indicates a small amount of anechoic fluid in the joint space.
Power Doppler image shows hyperemic blood flow in Power Doppler image shows hyperemic blood flow in the flexor tendon sheath in a patient with rheumatoid arthritis of the hands.

Two reports in the literature have explored a possible role for Doppler ultrasonography in evaluating arthritis, especially RA, on the basis of synovial hyperemia. Newman et al [34] used a 3-level semiquantitative approach by trained radiologists to grade Doppler flow subjectively in patients with RA, psoriatic arthritis, and calcium pyrophosphate deposition disease arthritis. The investigators found that the degree of abnormal tissue hyperemia visualized correlates grossly with the severity of local disease activity as measured by synovial-fluid white blood cell (WBC) counts and patients' subjective estimates of symptoms. The report did not include joint examinations or other physical/functional measurements.

Hau et al [35] from the University Hospital of Würzburg, Germany, reported findings from ultrasound in the MCP and PIP joints of 34 patients with RA and 15 control subjects over a 6-month period. In the protocol, each patient was examined only once. Patients were stratified into 3 groups based on swelling and tenderness. Ultrasonography was performed by using a Siemens Doppler unit and a 5- to 13-MHz linear-array transducer operating at 12 MHz. The authors identified joint pannus on gray-scale images as hypoechoic soft tissue adjacent to the articular surfaces and described the pannus distribution as favoring the radial side of the joints. Velocity color Doppler (ie, conventional direction-sensitive Doppler) imaging was used to evaluate vascularization and blood flow in the rheumatoid pannus as a surrogate marker of inflammation. The quantitation method used was analogous to that used by one of the coauthors of this article in preliminary studies.

A simple image-based quantification was obtained in the study by Hau et al [35] by summing the color pixels within all joints in each patient classification after selection of regions of interest within each joint. The result was a unitless numerical scale that showed a greater than tenfold difference between patients with active RA and controls. From the preliminary investigations, both the Newman and Hau studies [34, 35] concluded that power Doppler ultrasonography can reflect disease activity in RA, and each group suggested further research in this area.

Since 1999, several research groups have gone further in their development of power Doppler ultrasonography and its application to RA. Teh et al [36] evaluated quantitative power Doppler ultrasonography for the assessment of therapeutic response in rheumatoid synovitis in 13 consecutive patients over 7 months, with correlation to serum inflammatory markers and clinical evaluation. Quantitiative power Doppler spectra were derived within select regions of interest from each patient’s scan, both before and after treatment; essentially, the method used was an automated pixel-counting technique similar to that of Hau. There was extremely good correlation between the image-based quantitation of synovial hyperemia and the clinical and laboratory assessment of disease activity in this study.

Thus, quantitative power Doppler ultrasonography was able to accurately depict the patients’ response to treatment. The authors of the study felt that the addition of quantitative power Doppler ultrasonography to the routine assessment of therapeutic response in RA yielded more accurate findings than existing clinical and laboratory methods alone.

Strunk et al [37] compared quantified power Doppler ultrasonography with laboratory measurement of serum vascular endothelial growth factor (VEGF level) as markers for disease activity, finding a very high correlation (p< 0.0001) for ultrasound and no relation with the immediate serum VEGF level in the same patient. That same year, Salaffi et al [38] evaluated quantified power Doppler ultrasonography augmented by the use of IV ultrasound contrasts, such as Levovist, using a quantitative time-intensity curve integration to arrive at the quantification in arbitrary units. The results showed a correlation of the Doppler signal to other measures of disease and treatment efficacy.

Fukae et al studied the relation between synovial vascularity, assessed by quantitative power Doppler ultrasonography (PDUS), and structural bone damage in a single finger joint by comparing 190 metacarpophalangeal (MCP) and 190 proximal interphalangeal (PIP) joints of 19 patients with active RA who received disease-modifying antirheumatic drugs (DMARDs). The authors found that quantitative PDUS was significantly correlated with enhancement rate of MRI in each single finger joint. Comparing quantitative synovial vascularity and radiographic change in single MCP or PIP joints, the level of vascularity at baseline showed significant positive correlation with radiographic progression at the 20th week. Quantitative PDUS was found to be more useful than the semiquantitative method in evaluating synovial vascularity in a single finger joint. [39]

Fiocco et al [40] found that both C-reactive protein and Doppler findings reliably measured response to treatment with etancercept, an anti–tumor necrosis factor-alpha medication that has shown considerable efficacy in rheumatoid arthritis.

Research in this area is ongoing, but according to published reports, quantified power Doppler ultrasonography is a reproducible and reliable surrogate indicator of disease activity, which can predict and evaluate treatment response with a greater degree of sensitivity and specificity than other available clinical methodologies. [11, 24]


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