Musculoskeletal ultrasound (MSUS) has emerged as an invaluable diagnostic and prognostic tool in rheumatology, often complementing clinical evidence to bolster its role in managing patients with rheumatoid arthritis (RA) or juvenile idiopathic arthritis (JIA).^1-3 During the 28^th Hong Kong Medical Forum, Dr. Ho, Tze-Kwan Carmen, the Clinical Chief and Consultant of the Division of Rheumatology and Clinical Immunology at Queen Mary Hospital, shared her insights on the implementation of MSUS and the interpretation of its results in gout management.

Since its introduction for clinical use in 1972, MSUS has been widely utilized to assess rheumatic and musculoskeletal diseases. This can be attributed to its ability to detect pathology in joints, guide therapeutic procedures such as joint injection and aspiration, and correlate with magnetic resonance imaging (MRI) across multiple pathologies.¹ Furthermore, the advancement of technology, including enhanced image resolution and the availability of portable or laptop-sized ultrasound equipment, has led to an accelerated and widespread adoption of MSUS in rheumatology.¹ Dr. Ho described MSUS as a stethoscope for rheumatologists, offering a more comprehensive diagnosis and improvements in rheumatic disease management. “In Hong Kong, MSUS has been included in rheumatology training for the past 3 years,” she stated.

As a result of its growing significance, the quantity of MSUS-related literature has increased exponentially over the last decade, with over 2,000 publications evaluating its use in rheumatology.¹ Recent studies have found MSUS to be pivotal in evaluating synovial inflammation, assessing the risk of relapse in RA patients, and detecting disease activity and predicting flares in JIA patients.^2,3 “In patients with RA, MSUS has been demonstrated to be more reliable and sensitive than conventional clinical examinations of their joints, which is especially beneficial for the initial detection of RA,” Dr. Ho concluded.

In addition to its applications in RA and JIA, Dr. Ho highlighted that MSUS can also be applied to affirm gout diagnosis by identifying three distinct features: The double-contour sign (DCS), tophi, and aggregates. She defined DCS as an abnormal hyperechoic band over the hyaline cartilage, which indicates the presence of urate deposits. “Normally, only one bony contour can be observed in healthy joints. With the existence of urate deposits in the hyaline cartilage of gout patients' joints, an abnormal amount of ultrasound is obstructed during MSUS, leading to the additional bony contours on the final image,” Dr. Ho explained. While tophi can be detectable through clinical examinations, Dr. Ho expressed that they can also be identified via MSUS. In MSUS, tophi appear as hyperechoic or hypoechoic, heterogeneous material with poorly defined borders, often manifesting in extra- and intra-articular regions or even intratendinously. In contrast, Dr. Ho mentioned that aggregates, which are heterogeneous hyperechoic foci that retain a high degree of reflectivity, are comparatively less sensitive in the context of gout.

These three MSUS characteristics were considered the defining features of gout due to their accuracy and reproducibility, with the former two features being endorsed as a diagnostic parameter in the gout classification criteria established by the American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR).⁴ Dr. Ho added that another diagnostic advantage of MSUS is its ability to detect urate crystals in asymptomatic joints.

In conclusion, Dr. Ho stated that MSUS is capable of detecting urate crystals in patients' joints with a high degree of accuracy while being a non-invasive and radiation-free procedure. These advantages of MSUS facilitate a timely diagnosis of gout without compromising patient comfort, affirming its role as a reliable diagnostic tool. The exponential growth in MSUS-related literature and its widespread adoption in rheumatology, particularly in Hong Kong, further underscores the importance of this imaging modality in the management of rheumatic diseases.