Ultrasound in pediatric rheumatology: Highlighting the differences with adults

Abstract

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.

Figure 1.

Anatomical differences in a growing and adult long bone. Schematic outline of the structure of a typical long bone shows the gross anatomical characteristics of the distal part of the bone that will interact with the joint.

Figure 2. A, B.

Ultrasound images (grey-scale) of the radiocapitellar joint, showing normal anatomy of the elbow in a longitudinal-anterior view. (A) Three-year-old patient with incompletely ossified epiphysis. Notice the anechoic image of the metaphysis with the growth plate, along with the secondary ossification center in the epiphysis, surrounded by hyaline cartilage. (B) Six-teen-year-old patient with completely ossified epiphysis. Notice the anatomic changes in the epiphysis and how the articular cartilage has a different thickness. Asterisks (*) indicate a hyperechoic regular line, which is an interface artifact on hyaline cartilage. Images obtained using a GE Logiq S8 ultrasound with a linear probe of 4-15 MHz frequency. C, capitulum (humerus); R, radius.

Figure 3. A, B.

Sagittal ultrasound images (grey-scale) of the hip of a 3-year-old Juvenile idiopathic arthritis girl who had synovitis of the hip during the disease course. (A) Right hip with anechoic joint effusion (*) and synovial thickening. The anterior (A) and posterior (P) layers of the joint capsule are separated by the effusion, and there is distension of the joint capsule above the femoral neck. (B) Contralateral left hip (healthy) of the same patient. Images obtained using a GE Logiq S8 ultrasound with a linear probe of 4-15 MHz frequency.

Figure 4.

Ultrasound image (grey-scale and power Doppler) of the hip of a 4-year-old juvenile idiopathic arthritis patient who had synovitis of the joint during the disease course. Sagittal ultrasonography of the femoral head (FH), femoral neck (FN), the joint capsule (C), and an anechoic synovial effusion. Notice the bulging in the capsule above the femoral neck caused by the joint effusion. Doppler signal observed in the image is an artifact not related in this case with the pathological findings. Images obtained using a GE Logiq S8 ultrasound with a linear probe of 415 MHz frequency.

Figure 5.

A-C. Midsagittal ultrasound images (grey-scale and power Doppler) of dorsal wrists of juvenile idiopathic arthritis (JIA) patients of different ages. Images showing radiocarpal and midcarpal joints. (A) Five-year-old girl with oligoarticular JIA: anechoic synovial effusion (*) synovial hypertrophy and hypervascularization (part of the signal corresponds to physiological blood vessels and part of the signal is pathological); (B) 15-year-old girl with JIA: anechoic synovial effusion (*) synovial hypertrophy (arrows) and hypervascularization; (C) 19-year-old girl with polyarticular rheumatoid factor positive JIA: anechoic synovial effusion (*) synovial hypertrophy, hypervascularization and cortical bone irregularities (arrows), compatible with bone erosions (images of perpendicular planes not shown). R, radius; RE, distal-radial epiphysis; L, lunate; C, capitate; MC, metacarpal. Images obtained using a GE Logiq S8 ultrasound with a linear probe of 415 MHz frequency.