Ultrasound in pediatric rheumatology: Highlighting the differences with adults.

Musculoskeletal ultrasound (MSUS) is a powerful tool of major importance in rheumatology. MSUS is ideally suited for the evaluation of pediatric patients because it is a safe technique with a high patient acceptability, it does not require sedation, and it is excellent for exploring multiple joints. It is also the most operator-dependent imaging modality, and assessing joints in patients with juvenile idiopathic arthritis (JIA) is particularly challenging due to the unique features of the growing skeleton. Years ago, MSUS was already extensively used to manage rheumatoid arthritis (RA), which allowed pediatric rheumatologists to apply the knowledge generated in adult studies. It was a good starting point to study the joints of healthy children and JIA patients. Luckily, there is increasing evidence regarding the possibilities of MSUS in the management of JIA patients, with recent definitions for synovitis, descriptions of the sonographic features of joints in healthy children, and a better understanding of the role of subclinical synovitis. This review highlights the differences in normality and in pathological findings between children and adults assessed by MSUS. Specifically, this provides a summary of the current information on characteristics, scores, and definitions that are frequently different between JIA and RA patients. Despite the existence of several unresolved questions in the field, the value that MSUS adds to clinical examination in JIA has already been demonstrated, and we believe that MSUS may be included in the near future in treatment to target strategies.