“With proper management, gout flares induced by the deposition of monosodium urate (MSU) crystals can be prevented, joint damage can be minimized, and existing crystal depositions can be dissolved,” explains Sara Nysom Christiansen, MD, PhD. “Studies suggest, however, that to a wide extent, gout management remains suboptimal, partly due to insufficient monitoring of gout lesions.”

Ultrasound, commonly used to detect changes in MSU deposition in patients with gout, can assist physicians by showing if there has been a reduction in MSU crystals, Dr. Christiansen notes. “A binary ultrasound scoring system can detect the disappearance of gout lesions during urate-lowering therapy,” she says. “However, enabling the detection of gradual reduction of MSU deposition requires more sensitive measures, such as a semi-quantitative ultrasound scoring system. The development of this type of system for gout-specific lesions is essential.”

Aggregates Showed Lowest Reliability of All Gout Lesions

For a paper published in Seminars in Arthritis and Rheumatism, Dr. Christiansen and colleagues aimed to develop a new ultrasound definition for aggregates (small crystal depositions), as well as a semi-quantitative ultrasound scoring system for gout-specific ultrasound lesions: double contour sign (deposits of crystals on the cartilage surface), tophus (larger crystal depositions), and aggregates.

Prior to the study, the Outcome Measure in Rheumatology (OMERACT) ultrasound working group developed and validated consensus-based definitions of gout-specific ultrasound lesions. “Overall, aggregates had the lowest reliability of all of the OMERACT-defined ultrasound gout lesions,” Dr. Christiansen says, adding that the inter-reading reliability of aggregates was especially low. “Therefore, besides developing a semi-quantitative scoring system for the ultrasound gout lesions and testing its reliability, we sought to redefine the aggregates to improve their definition. We wanted to test the reliability of the redefined aggregates—as assessment of these is part of semi-quantitative scoring system—and to test the reliability of the scoring system.”

A Delphi survey method was used for redefining aggregates and for selecting a semi-quantitative scoring system with a greater than 75% agreement obligate for reaching consensus, Dr. Christiansen explains. A Web-based exercise on static ultrasound images was conducted to assess the reliability of both the redefined aggregates and the semi-quantitative scoring system. Twenty rheumatologists from 14 countries in Europe, America, and Australasia contributed to all rounds of the Delphi process and image exercises, and a consensus-based, semi-quantitative ultrasound gout scoring system was developed after two Delphi rounds.

A Step Toward a Reliable Ultrasound Scoring System

The new definition of aggregates and the ultrasound gout scoring system were reliable when tested in static images, according to Dr. Christiansen. “This study is the first step toward a novel, reliable, semi-quantitative ultrasound scoring system available to clinicians and sonographers assessing patients with gout during urate-lowering therapy,” she says.

The study team developed an overarching principle stressing that aggregates can only be scored in patients with other ultrasound gout-specific features, Dr. Christiansen adds. “This emphasizes that the appearance of aggregates is non-specific for gout; hence, the aggregates alone have no diagnostic value in patients with gout,” she says (Table).

In routine clinical practice, ultrasound monitoring of patients with gout during treatment can indicate if the desired reduction of crystals is achieved, Dr. Christiansen adds. “However, for a fully operational monitoring tool to meet the OMERACT requirements, the scoring system also needs to be valid for grading lesions in dynamic scans of patients. Therefore, the next step in the validation process would be a patient-based reliability exercise.”

Besides being an effective tool for the diagnosis and monitoring of patients with gout, ultrasound could potentially be an important tool for improving patient compliance with gout treatment, Dr. Christiansen continues. “Studies have shown that patient adherence to urate-lowering therapy is often very poor,” she notes. “A patient’s understanding of the chronic deposition of MSU crystals as the cause of gout and the rationale for long-term urate-lowering therapy is crucial to improving gout management. Future studies focusing on the effect of ultrasound examination on patient compliance could be very interesting.”