Differential diagnosis of inflammatory arthritis from musculoskeletal ultrasound view

Diagnostic imaging in rheumatology has evolved over the centuries, and novel imaging modalities, including musculoskeletal ultrasonography (MSUS) and magnetic resonance imaging (MRI), are being widely used in the 21st century. With the increase in availability of molecular target-specific therapies, including biologic agents and Janus kinase (JAK) inhibitors, the therapeutic outcome of inflammatory arthritis has changed, and early and accurate diagnosis of inflammatory rheumatic diseases has become more important. Given this situation, MSUS, which is a portable, convenient, noninvasive, and cost-effective imaging technique, plays an important role in the diagnosis of rheumatic diseases. MSUS can be used to detect subclinical inflammation and to accurately determine the distribution of joint involvement and inflammation sites in each joint. Definitive diagnosis for patients with early arthritis should be made after noting their history and performing clinical examination, laboratory testing, and additional procedures. However, MSUS is an extension of physical examination and it can provide a further opportunity and motivation to consider differential diagnoses rather than a conclusive diagnosis. This review aims to describe the usefulness of MSUS in differential diagnoses of the phenotype of early inflammatory arthritis.