<p><strong>BACKGROUND: </strong>Observations among Israeli pediatric rheumatologists reveal that pediatric Juvenile Spondyloarthritis (JSpA) may present differently compared to patients from the United States (US). This study is aimed to compare the demographic and clinical variables of Israeli and US JSpA patients upon presentation.</p>

<p><strong>METHODS: </strong>We performed a retrospective, cross-sectional, multicenter comparison of JSpA patients among 3 large Israeli pediatric rheumatology centers and a large US pediatric rheumatology center. Patients with diagnosis of Juvenile Ankylosing Spondylitis (JAS) and/or Enthesitis-related Arthritis (ERA) were included. The demographic, clinical and radiologic features were compared.</p>

<p><strong>RESULTS: </strong>Overall 87 patients were included (39 Israeli, 48 US patients). Upon presentation, inflammatory back pain, sacroiliac joint tenderness and abnormal modified Schober test, were significantly more prevalent among Israeli patients (59% vs. 35.4, 48.7% vs. 16.7, and 41.2% vs. 21.5%, respectively, all p &lt; 0.05), whereas peripheral arthritis and enthesitis were significantly more prevalent among US patients (43.6% vs. 91.7 and 7.7% vs. 39.6% in Israeli patients vs. US patients, p &lt; 0.05). In addition, 96.7% of the Israeli patients versus 29.7% of the US patients demonstrated sacroiliitis on MRI (p &lt; 0.001, N = 67). Less than one-third of the Israeli patients (32%) were HLA-B27 positive vs. 66.7% of US patients (p = 0.007).</p>

<p><strong>CONCLUSION: </strong>Israeli children with JSpA presented almost exclusively with axial disease compared to US patients who were more likely to present with peripheral symptoms. HLA B27 prevalence was significantly lower in the Israeli cohort compared to the US cohort. Further studies are needed to unravel the genetic and possibly environmental factors associated with these findings.</p>

<p><strong>OBJECTIVE: </strong>Magnetic resonance imaging (MRI) is pivotal in the assessment of early sacroiliitis in children. We aimed to evaluate the agreement between local radiology reports and central imaging reviewers for active inflammation and structural damage at the sacroiliac joints (SIJs).</p>

<p><strong>METHODS: </strong>Eight hospitals each contributed up to 20 cases of consecutively imaged children and adolescents with juvenile idiopathic arthritis and suspected sacroiliitis. Studies were independently reviewed by 3 experienced musculoskeletal pediatric radiologists. Local assessments of global impression and lesions were coded from the local radiology reports by two study team members. Test properties of local reports were calculated using the central imaging team's majority as the reference standard.</p>

<p><strong>RESULTS: </strong>For 120 evaluable subjects, median age was 14 years, half of cases were male, and median disease duration at time of imaging was 0.8 years (IQR: 0-2). Sensitivity, 93.5% (95% CI: 78.6-99.2%), and specificity, 69.7% (95% CI: 59.0-79.0%), of local reports for inflammation were high and moderate, respectively, but positive predictive value (PPV) was low 51.8% (95% CI: 38.0-65.3%). Twenty-seven (23%) cases had active inflammation reported locally but rated normal centrally, nineteen (70%) with subsequent medication changes. Sensitivity of local reports detecting structural damage was low, 45.7% (95% CI: 28.8-63.4%), and specificity, 88.2% (95% CI: 79.4-94.2%), was high; PPV was low 61.5% (95% CI: 40.6-79.8%).</p>

<p><strong>CONCLUSION: </strong>Substantial variation exists in the interpretation of inflammatory and structural lesions at the SIJs in children. In order to reliably identify pathology, additional training in the MR appearance of the maturing SIJ is greatly needed.</p>

<p><strong>BACKGROUND: </strong>The SPARCC sacroiliac joint inflammation (SIS) and structural (SSS) scores are reliable measures to quantify abnormalities in the pediatric sacroiliac joint. We aimed to evaluate the utility of online calibration modules for the SIS and SSS and the reliability of their component change scores.</p>

<p><strong>METHODS: </strong>Change score reliability of 6 raters was assessed by overall and pairwise intraclass correlation coefficients (ICCs) before and after the use of real-time iterative calibration (RETIC) modules for both the SIS and SSS comprised of 20 adult cases. Acceptable ICC for change scores was &gt; 0.7 for SIS and &gt; 0.5 for all SSS components. Sensitivity to change was assessed by the standardized response mean (SRM).</p>

<p><strong>RESULTS: </strong>In scoring exercise 1, the SIS had acceptable reliability with a change score ICC of 0.80 and sclerosis was the only SSS lesion that met the acceptability threshold with a change score ICC of 0.52. After RETIC calibration, the SIS overall (ICC = 0.83) and mean pairwise (ICC = 0.83) change scores remained reliable with a large SRM (0.90). All SSS components except sclerosis met the overall and mean pairwise change score ICC acceptability thresholds-backfill: overall = 0.54, mean pairwise = 0.50; fat metaplasia: overall = 0.65, mean pairwise = 0.57; erosion: overall = 0.60, mean pairwise = 0.58; and ankylosis: overall = 0.96, mean pairwise = 0.96. The SSS RETIC module augmented the number of SSS components surpassing the acceptability threshold from 1 to 4. Sensitivity to change, as measured by the SRM, was large for erosion (0.96), moderate for backfill (0.55) and sclerosis (0.70), and small for fat metaplasia (0.36) and ankylosis (0.28).</p>

<p><strong>CONCLUSION: </strong>RETIC modules improved the overall reliability of SPARCC SIS and SSS change scores for previously calibrated raters. SIS recalibration was not as helpful to the most experienced raters who achieved high levels of agreement before recalibration. The SPARCC SIS and all SSS components except sclerosis are reliable measures to quantify change over time in children. A pediatric-specific RETIC tool should be developed to enhance the calibration of readers.</p>