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Musculoskeletal Imaging

E2344. Musculoskeletal Ultrasound in the Diagnosis of Acute Crystalline Arthropathy

Sever A,  Rheinboldt M. Henry Ford Hospital, Detroit, MI

Address correspondence to M. Rheinboldt (mrheinbold@yahoo.com)

Background Information: Both gout and calcium pyrophosphate deposition (CPPD) disease are common metabolic arthropathies, presenting not only diagnostic but management challenges as well. Though histologic crystal aspiration is definitive, diagnosis is commonly established through a composite of clinical features and laboratory findings. Musculoskeletal ultrasound has a contributory and growing role not only in routine disease surveillance but also in helping render a timely and specific diagnosis for patients presenting with new onset oligoarticular arthritis in the emergency setting. In this presentation, we review the various general and characteristic ultrasound features of crystalline arthropathy as well as the published data in regard to sonographic performance metrics.

Educational Goals/Teaching Points: Our aim is to discuss the demographics, laboratory, and clinical features of both gout and calcium pyrophosphate–related arthropathy. We briefly review meta-analysis data and Outcome Measures in Rheumatology (OMERACT) consensus statements on the role of ultrasound in the diagnosis and management of gout and illustrate both nonspecific and characteristic discriminatory sonographic features of gout and calcium pyrophosphate–related arthropathy. We discuss potential roles for sonography in synovial biopsy and therapeutic injection guidance.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: Sonographic features relevant to gout and CPPD can be divided into specific and nonspecific findings including joint effusion, synovial hypertrophy, and erosions. Ultrasound has been shown to have greater sensitivity for the presence of early erosive changes of gout than radiographs, in which erosions may take 6 to 12 years to manifest. Typical locations include the medial side of the first metatarsophalangeal joint and the metacarpophalangeal joints. The double contour sign is a primary discriminating feature for gout versus CPPD. Monosodium urate crystals within a supersaturated effusion precipitate mainly in the superficial hyaline cartilage layer, forming a hyperechoic line along the outer margin, independent of the angle of insonation and paralleling the subjacent bone interface. In contrast, calcium pyrophosphate crystals have a predilection for the central hyaline cartilage layer. The precipitation of monosodium urate and calcium pyrophosphate crystals within a joint effusion gives an echogenic “snowstorm” appearance to the fluid. Crystal formation within synovial tissue and soft tissue structures may occur, similarly increasing regional echogenicity and shadowing. Distribution of findings aids in diagnosis, with CPPD favoring the triangular fibrocartilage of the wrist and knee menisci. Tophi have a variable appearance, initially hypoechoic and later developing distal acoustic shadowing. Common locations include the first metatarsophalangeal joint, wrists, fingers, knees, and ankles.

Conclusion: Current literature and clinical experience supports the additive value and use of musculoskeletal ultrasound in the diagnosis of acute crystalline arthropathy. A thorough understanding of the characteristic sonographic features potentially encountered allows the radiologist a growing role in the work-up and management of this patient cohort.