Ultrasound imaging for sternoclavicular joint involvement in enthesitis-related arthritis: A closer look at capsular enthesitis.

Introduction: Enthesitis-related arthritis is a specific subtype of juvenile idiopathic arthritis characterised by the co-presence of arthritis and enthesitis or the evidence of one of them coupled with at least two among sacroiliac joint tenderness, inflammatory back pain, presence of human leukocyte antigen-B27, acute symptomatic anterior uveitis, onset in a male child aged 6 years or older or history of spondyloarthropathy in a first-degree relative. Small joints like the sternoclavicular joint are rarely affected, and the prevalence of their involvement in enthesitis-related arthritis has been poorly assessed in the pertinent literature.

Case report: The authors report an atypical case of left sternoclavicular joint arthritis/enthesitis in a 12-year-old male child with juvenile idiopathic arthritis. The B-mode sonographic findings of articular effusion, synovial hypertrophy and capsular bulging, coupled with the microvascular mapping with colour Doppler of the sternoclavicular joint, have been crucial to optimising the pharmacological approach in clinical practice. In this sense, the sonographic examination presented as a natural extension of the physical examination to accurately define the poor control of disease activity using first-line pharmacological agents.

Discussion: The present case report can be considered the first to accurately report the B-mode and the colour Doppler findings of a pathological sternoclavicular joint in a patient enthesitis-related arthritis. Ultrasound imaging demonstrated intra-articular effusion, capsular bulging and synovial hypertrophy clearly defining sternoclavicular joint arthritis. Interestingly, the hypervascularisation involved both the synovial tissue and the capsule-bone interface - that is, the enthesis of the joint capsule - suggesting a potential co-existence of arthritis and enthesitis of the sternoclavicular joint in enthesitis-related arthritis patients.

Conclusion: The high-resolution point-of-care ultrasound seems to be a potential 'game changer' in paediatrics to promptly optimise the pharmacological management in enthesitis-related arthritis patients. Indeed, unlike other imaging modalities such as magnetic resonance imaging, modern high-frequency ultrasound transducers guarantee a superior spatial resolution of superficial joints and allow an accurate mapping of small-size and low-flow vascular elements of synovial and capsular tissues optimising the grading of disease activity and avoiding the use of contrast agent.