Spinal involvement in juvenile idiopathic arthritis: what do we miss without imaging?

Juvenile idiopathic arthritis (JIA) is the most common chronic rheumatic disease of childhood. Enthesitis-related arthritis (ERA) has been one of the most controversial subtypes of JIA with a higher risk of axial involvement.  Our aim was to assess the frequency and spectrum of MRI findings of spine involvement in patients with JIA and determine if the axial involvement is always clinically symptomatic in patients with positive MRI findings. In this retrospective cross-sectional observational study we included known or suspected JIA patients who underwent spinal MRI examination between 2015 and 2017 and followed up in the Pediatric Rheumatology outpatient clinic. The demographic and clinical data were reviewed from the medical charts and electronic records. All patients were grouped as clinically symptomatic and asymptomatic for spinal involvement and MRI findings were re-evaluated for presence of inflammatory and erosive lesions. Of the 72 JIA patients, 57 (79.2%) were diagnosed with ERA, and 15 (20.8%) with non-ERA subtypes of JIA. Overall, 49 (68%) patients with JIA had positive spinal MRI findings (inflammatory and/or erosive lesions). Twenty-seven (47%) ERA patients were clinically symptomatic for spine involvement and among them, 19 (70.3%) had positive spinal MRI findings. Although 30 ERA (53%) patients were clinically asymptomatic, 23 of them (77%) had positive spinal MRI findings, as well. Eleven (73%) patients diagnosed with non-ERA JIA subtypes were clinically symptomatic for spine involvement at the time of MRI. Among them, four (36.3%) had inflammatory and/or erosive lesions on spine MRI. Four (26%) non-ERA patients were clinically asymptomatic for spine involvement, but three (75%) of them showed positive findings on spinal MRI. Inflammatory and/or erosive lesions of the thoracolumbar spine could exist in patients with JIA, regardless of the presence of symptoms. Not only because the significant proportion of ERA patients show asymptomatic axial involvement but also the presence of axial involvement in patients who were classified as non-ERA depending on current ILAR classification underlines the necessity of using MRI for accurate classification of patients with JIA.