Musculoskeletal ultrasound for gout diagnosis: Why and how?

While monosodium urate monohydrate crystals in synovial fluid is the gold standard for gout diagnosis, imaging evidence of urate deposition in the joint or bursae on ultrasonography or dual-energy CT (DECT) is also included in the classification criteria of the American College of Rheumatology and European League Against Rheumatism. [Arthritis Rheumatol 2015;67:2557-2568]

“Given its noninvasive and radiation-free nature as well as and cost-effectiveness, MSUS is preferred over DECT for detecting urate deposition [in our practice],” said Dr Carmen Ho of the Division of Rheumatology and Clinical Immunology, Queen Mary Hospital, Hong Kong, at HKMF 2024. [Clin Exp Rheumato 2018;36(Suppl 114):3-9]

Key MSUS imaging features in gout include:

1.         Double contour sign: Abnormal hyperechoic band over the superficial margin of the articular hyaline cartilage, independent of the angle of insonation. It may appear irregular or regular, continuous or intermittent, and can be distinct from the cartilage interface sign.

2.         Tophus: A circumscribed, inhomogeneous, hyperechoic and/or hypoechoic aggregation, which may be surrounded by a small anechoic rim. It can be detected in extra-articular, intra-articular or intra-tendinous regions.

3.         Aggregates: Heterogeneous hyperechoic foci that maintain a high degree of reflectivity in the intra-articular or intra-tendinous regions. [Rheumatology (Oxford) 2015;54:1797-1805]

These MSUS features are highly reproducible and validated for diagnosing gout. Notably, patients with asymptomatic hyperuricaemia may also exhibit the double contour signs and tophus on MSUS. [Ann Rheum Dis 2014;73:1522-1528; Semin Arthritis Rheum 2016;45:570-579; Arthritis Care Res (Hoboken) 2017;69:875-883; Semin Arthritis Rheum 2019;49:62-73]

“In my experience, MSUS detected double contour signs in the talus of a male patient with a history of degenerative knee joint who was initially misdiagnosed as having osteoarthritis by a family doctor. Following diagnosis of gouty arthritis with MSUS and subsequent confirmation of high urate levels, the patient was started on urate-lowering therapy,” Ho shared.

“Patients with [asymptomatic] hyperuricaemia should undergo imaging assessment, such as MSUS, to detect urate deposition,” she suggested. “Once diagnosed, it is crucial to discuss further management, including the potential need for lifelong urate-lowering therapy.”

“Precise diagnosis of gout using MSUS requires skilled operational techniques. For example, manual adjustment is essential to distinguish signals for aggregation and synovium,” Ho pointed out. In Hong Kong, MSUS has been incorporated into the rheumatology training curriculum since July 2021. [J Ultrasound 2021;24:151-156; https://www.rheumatology.org.hk/sig-overview/msus]