ESR Essentials: juvenile idiopathic arthritis; what every radiologist needs to know-practice recommendations by the European Society of Paediatric Radiology.

Juvenile Idiopathic Arthritis (JIA) is a major contributor to chronic diseases, affecting around 1-2 in 1000 children under the age of 16. With modern treatments, the morbidity has been reduced; however, there is increasing evidence that many, if not most, children with JIA will have a chronic disease with ongoing activity into adulthood. Many studies discuss the possibility of an early window of opportunity in which patients have the best chance of responding to therapy, thereby underscoring the importance of timely and appropriate imaging. Children typically present at 4-5 years of age with one or more stiff and painful joints. If JIA is suspected, the child should undergo an ultrasound of the involved joint(s), performed by a radiologist with experience in paediatric imaging. If this is normal, with no abnormal laboratory tests and low clinical suspicion of JIA, no further imaging is required. If there is inconsistency between ultrasound and clinical findings, then they should proceed to MRI, including intravenous contrast, of the involved joint. Additional radiographs, or low-dose CT for the axial joints to examine for potential destructive change, deformation, or growth abnormalities, should be considered. In children presenting with monoarthritis, bacterial infection must be ruled out. KEY POINTS: Ultrasound is the initial modality in the diagnosis of JIA, and if there is inconsistency between ultrasound and clinical findings, MRI should be performed. Radiography for the assessment of destructive change, deformity, and malalignment should be considered, alternatively, low-dose CT for the temporomandibular and sacroiliac joints and the cervical spine. Knowledge of normal imaging features in children is mandatory.