COMMENTARY

Ultrasound for Gout, RA, and Other Forms of Arthritis

Lisa Vasanth, MD, MS

Disclosures

May 14, 2015

Introduction

The diagnostic potential of musculoskeletal ultrasound in rheumatology was recognized as early as 1972 in a report that documented the use of ultrasound to differentiate a Baker's cyst from thrombophlebitis.[1] Despite its advantages over other imaging modalities including low cost, real-time assessment, patient comfort, and lack of radiation, the use of musculoskeletal ultrasound as more than a tool to guide procedures was not widely adopted by rheumatologists in the United States until recently. Limitations to the implementation of ultrasound included cost of equipment, limited availability of training programs, time required to become an accurate and effective operator, lack of standardized protocols to diagnose and monitor musculoskeletal conditions, and the availability of other imaging modalities.

Today, machines have become more portable, less costly, and easier to use. Structured musculoskeletal ultrasound training is now available to rheumatology fellows and those in practice.[2,3,4] Ultrasound protocols have been developed and validated for use in the diagnosis of rheumatologic disease and the assessment of a patient's response to treatment.[5] In the past 5 years, the American College of Rheumatology (ACR) and the European League Against Rheumatism (EULAR) have updated the classification criteria for a number of rheumatologic conditions. Many of these new classification criteria contain imaging domains with ultrasound findings.

Musculoskeletal ultrasound as an aid for diagnosis and monitoring response to treatment is most widely used in rheumatoid arthritis (RA). Early detection and treat-to-target strategies are known to prevent joint damage and functional impairment in patients with RA.[6] In 2010, ACR/EULAR removed radiographic erosions from the RA classification criteria because x-ray erosions are a late finding signifying joint damage that can potentially be averted with new treatment methods.[7] The 2010 ACR/EULAR RA criteria underscore the importance of synovitis, requiring at least one swollen joint for diagnosis, and giving the most weight to joint involvement.[7] The authors suggest that the clinical findings of swollen and tender joints "may be confirmed by imaging evidence of synovitis."[7]

Multiple groups, including Outcome Measures in Rheumatology (OMERACT) and the EULAR Musculoskeletal Ultrasound working group (EULAR MSKUS), have developed standard ultrasound definitions for synovitis and other ultrasound evidence of RA disease activity, including erosions, tenosynovitis, and power Doppler signal.[8] Scoring systems are under development to quantify the amount of RA disease activity. These include the comprehensive ultrasound 7-joint score[9] or 12-joint score[4] and a Power Doppler-only 8-joint score for daily practice.[10] In a study of patients with early RA (< 3 years of symptoms), Nakagomi and colleagues[11] found that the ultrasound 12-joint score could improve the ability of the 2010 ACR/EULAR criteria to predict which patients would require treatment with the disease-modifying agent methotrexate within 1 year. They also found that the use of ultrasound to confirm synovitis changed the disease classification in a subset of their single-center cohort. Seventeen patients (15.6%) who did not fulfill criteria without ultrasound were reclassified as having RA with ultrasound criteria, and seven patients (6.4%) were reclassified from having RA to not having RA.[11]

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