<p><strong>BACKGROUND: </strong>While magnetic resonance imaging (MRI) of the pelvis and hips is common in pediatric patients, to date there are no data on the quantification of normal hip joint fluid volume in this patient population.</p>

<p><strong>OBJECTIVE: </strong>We sought to assess the feasibility and reliability of quantitative hip joint fluid measurement in the pediatric population to estimate the normal volume of fluid in a pediatric hip joint.</p>

<p><strong>MATERIALS AND METHODS: </strong>Seventy healthy children ages 8-17&nbsp;years underwent a pelvic MRI including a large field of view coronal T2 fat-saturated sequence where hips were entirely imaged. Following 3 training sessions, 2 readers with experience in musculoskeletal imaging performed volumetric quantitative measurements of hip fluid (140 hips) using semiautomated pixel-based thresholding on custom MATLAB software.</p>

<p><strong>RESULTS: </strong>The mean processing time per hip was 2&nbsp;min, 41&nbsp;s. The mean volume of fluid in a hip joint was 2.1&nbsp;mL (range: 0.38-5.41&nbsp;mL), increasing slightly with age. Volumes were also greater in boys than in girls (P=0.004). Intra-observer and interobserver agreement were high (intra-class correlation coefficients 0.93 and 0.98, respectively), with mean volume differences of 0.04&nbsp;mL for intra-observer and 0.09&nbsp;mL for interobserver.</p>

<p><strong>CONCLUSION: </strong>A semiautomated pixel-based thresholding approach was feasible and reliable for measuring joint fluid in pediatric hip MRI. The average fluid volume of 2.1&nbsp;mL can represent a visually substantial quantity of fluid per MRI slice, particularly in small children, and should not be misinterpreted as a joint effusion.</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>

<p><strong>Background: </strong>Relatively little is known about the epidemiology of juvenile psoriatic arthritis (PsA), including clinical features associated with the development of arthritis among children with psoriasis and subsequent risk of inflammatory comorbidities.</p>

<p><strong>Objective: </strong>To identify the overall risk of arthritis among children with psoriasis and subsequent risk of inflammatory comorbidities.</p>

<p><strong>Methods: </strong>Using Clinformatics™ DataMart (OptumInsight, Eden Prairie, MN) de-identified US administrative claims data from 2000-2013, we identified children 0-16 years with an incident diagnosis of psoriasis or PsA using ICD-9-CM diagnostic, procedure and pharmacy billing codes. Cox proportional hazard regression was performed to assess clinical features associated with development of arthritis in children with psoriasis. Incidence rate ratios were used to compare the relative frequency of co-morbid diagnoses.</p>

<p><strong>Results: </strong>We identified 212 children with PsA, 4,312 with psoriasis-only, and 45,240 controls. Approximately 33% of children with PsA received a diagnostic code for psoriasis before arthritis. Median time to index code for arthritis after index code for psoriasis was 17.6 months (IQR 4.1-38.1). Older age and uveitis were associated with a significantly increased risk of developing arthritis in children with psoriasis. Children with PsA had a significantly increased risk of uveitis, diabetes, and depressive disorder when compared to patients with psoriasis and inflammatory bowel disease, uveitis, diabetes, and depressive disorder when compared to controls.</p>

<p><strong>Conclusion: </strong>Most children with PsA developed arthritis first. Older age and uveitis were risk factors for arthritis among children with psoriasis. PsA was associated with increased risk of several clinically relevant inflammatory comorbidities.</p>

<p><strong>OBJECTIVE: </strong>Increasing reliance on MRI for the evaluation of sacroiliitis requires that radiologists be familiar with the normal appearance of the developing sacroiliac joint. We describe age-related MRI features of the sacroiliac joints in healthy children.</p>

<p><strong>SUBJECTS AND METHODS: </strong>Seventy healthy children from three age groups-prepubertal (8-10 years), peripubertal (11-13 years), and approaching skeletal maturity (14-17 years)-completed questionnaires and underwent sacroiliac joint MRI. Imaging studies were evaluated by three experienced pediatric radiologists. Metaphyseal-equivalent signal intensity, nonperiarticular osteitis, cartilage volume, joint fluid, enthesitis, and surface cortex irregularities were evaluated. Metaphyseal-equivalent signal intensity was evaluated using an ordinal grading system (types I-IV). Intraclass correlation coefficients were calculated to assess interrater reliability.</p>

<p><strong>RESULTS: </strong>Increased metaphyseal-equivalent signal intensity (types I and II) was present in most prepubertal children and in less than 10% of the group approaching skeletal maturity. More prepubertal girls had type I signal than boys, but signal progressed to type IV signal faster in girls than in boys. None of the subjects had subchondral marrow edema, but four subjects had nonperiarticular osteitis. Cartilage volumes decreased with advancing age in girls and, on average, were lower in girls than in boys of the same age. One subject had measurable joint fluid. Cortex irregularities were common (57.1%), most frequently seen along the iliac bone (51.4% ilium vs 11.4% sacrum, p &lt; 0.01) and in the upper quadrants (42.8% upper vs 27.1% lower, p = 0.01).</p>

<p><strong>CONCLUSION: </strong>We provide valuable reference MRI descriptions of the healthy pediatric sacroiliac joint that should improve our ability to distinguish between normal and pathologic findings.</p>

<p><strong>BACKGROUND: </strong>We aimed to evaluate the diagnostic utility of pelvic radiographs versus magnetic resonance imaging (MRI) of the sacroiliac joints in children with suspected sacroiliitis.</p>

<p><strong>METHODS: </strong>This was a retrospective cross-sectional study of children with suspected or confirmed spondyloarthritis who underwent pelvic radiograph and MRI within 6 months of one another. Images were scored independently by five raters. Interrater reliability was calculated using Fleiss's kappa coefficient (κ). Test properties of radiographs for depiction of sacroiliitis were calculated using MRI global sacroiliitis impression as the reference standard.</p>

<p><strong>RESULTS: </strong>The interrater agreement for global impression was κ = 0.34 (95% CI 0.19-0.52) for radiographs and κ = 0.72 (95% CI 0.52-0.86) for MRI. Across raters, the sensitivity of radiographs ranged from 25 to 77.8% and specificity ranged from 60.8 to 92.2%. Positive and negative predictive values ranged from 25.9 to 52% and from 82.7 to 93.9%, respectively. The misclassification rate ranged from 6 to 17% for negative radiographs/positive MRI scans and from 48 to 74% for positive radiographs/negative MRI scans. When the reference standard was changed to structural lesions consistent with sacroiliitis on MRI, the misclassification rate was higher for negative radiographs/positive MRI scans (9-23%) and marginally improved for positive radiographs/negative MRI scans (33-52%).</p>

<p><strong>CONCLUSION: </strong>Interrater reliability of MRI was superior to radiographs for global sacroiliitis impression. Misclassification for both negative and positive radiographs was high across raters. Radiographs have limited utility in screening for sacroiliitis in children and result in a significant proportion of both false negative and positive findings versus MRI findings.</p>

<p><strong>OBJECTIVE: </strong>There is a critical need for measures to evaluate structural progression in the pediatric sacroiliac joint (SIJ). We aimed to evaluate the construct validity and reliability of the Spondyloarthritis Research Consortium of Canada SIJ Structural Score (SSS) in children with suspected or confirmed juvenile spondyloarthritis.</p>

<p><strong>METHODS: </strong>The SSS assesses structural lesions of the SIJ on magnetic resonance imaging (MRI) through the cartilaginous part of the joint. We conducted 3 sequential reading exercises with 6 readers (1 adult and 3 pediatric radiologists, 1 adult and 1 pediatric rheumatologist). Each exercise was preceded by a calibration module. Interobserver reliability was assessed using intraclass correlation coefficients (ICC). Prespecified acceptable reliability thresholds were ICC &gt; 0.5 for erosion, backfill, and sclerosis, and ICC &gt; 0.7 for ankylosis and fat metaplasia.</p>

<p><strong>RESULTS: </strong>The SSS had face validity and was feasible to score in pediatric cases for all 3 reading exercises. Of the cases used in the 3 exercises, 58% were male and the median age was 14 years (range 6.8-18.7 yrs). After calibration, median ICC across all readers for each SSS component were the following: erosion 0.67 (interquartile range 0.54-0.80), backfill 0.33 (0.19-0.52), fat metaplasia 0.74 (0.62-0.85), sclerosis 0.63 (0.48-0.77), and ankylosis 0.44 (0.28-0.62). Prespecified reliability thresholds were achieved in the third exercise for erosion, sclerosis, and fat metaplasia but not for backfill or ankylosis.</p>

<p><strong>CONCLUSION: </strong>The SSS was feasible to score and had acceptable reliability for pediatric SIJ MRI evaluation. The ICC improved with additional calibration and reading exercises, even for readers with limited experience.</p>

<p><strong>BACKGROUND: </strong>Published methods for quantification of magnetic resonance imaging (MRI) evidence of inflammation in the sacroiliac joint lack validation in pediatric populations. We evaluated the reliability and construct validity of the Spondyloarthritis Research Consortium of Canada (SPARCC) sacroiliac joint inflammation score (SIS) in children with suspected or confirmed juvenile spondyloarthritis (JSpA).</p>

<p><strong>METHODS: </strong>The SPARCC SIS measures the presence, depth, and intensity of bone marrow inflammation on MRI through the cartilaginous part of the joint. Six readers blinded to clinical details except age, participated in two reading exercises, each preceded by a calibration exercise. Inter-observer reliability was assessed using intraclass correlation coefficients (ICCs) and for pre-specified acceptable reliability the inraclass correlation coefficient (ICC) was &gt; 0.8.</p>

<p><strong>RESULTS: </strong>The SPARCC SIS had face validity and was feasible to score in pediatric cases in both reading exercises. Cases were mostly male (64%) and the median age at the time of imaging was 14.9 years. After calibration, the median ICC across all readers for the SIS total score was 0.81 (IQR 0.71-0.89). SPARCC SIS had weak correlation with disease activity (DA) as measured by the JSpADA (r = - 0.12) but discriminated significantly between those with and without elevated C-reactive protein (p = 0.03).</p>

<p><strong>CONCLUSION: </strong>The SPARCC SIS was feasible to score and had acceptable reliability in children. The ICC improved with additional calibration and reading exercises, for both experienced and inexperienced readers.</p>

<p><strong>OBJECTIVE: </strong>To characterize the effect of anti-tumor necrosis factor (TNF) therapy compared to conventional synthetic disease-modifying antirheumatic drugs (csDMARD) in children with enthesitis-related arthritis (ERA) over the first year after diagnosis.</p>

<p><strong>METHODS: </strong>We conducted a multicenter retrospective comparative effectiveness study of children diagnosed with ERA. We estimated the effect of anti-TNF therapy on clinical variables (active joint count, tender entheses count) and patient-reported pain and global assessment of disease activity over the first year after diagnosis using state-of-the-art comparative effectiveness analytic methods.</p>

<p><strong>RESULTS: </strong>During the study period, 217 patients newly diagnosed with ERA had a total of 965 clinic visits the first year after disease diagnosis. Children [median age 11.6 yrs, interquartile range 10-14] were treated with anti-TNF monotherapy (n = 33, 15.2%), csDMARD monotherapy (n = 73, 33.6%), or both (n = 52, 23.9%) in the first year after disease diagnosis. There was a statistically significant improvement in the primary outcome, active joint count, over time in children who received an anti-TNF drug versus those who did not (p = 0.03). Additionally, use of anti-TNF therapy versus no anti-TNF therapy was associated with less patient-reported pain (p &lt; 0.01) and improved disease activity over time as assessed by the clinical Juvenile Arthritis Disease Activity Score (p &lt; 0.01). The magnitude of estimated effect on clinical outcomes was uniformly greater, with the exception of tender entheses count, in children treated with an anti-TNF drug versus a csDMARD.</p>

<p><strong>CONCLUSION: </strong>During the first year after diagnosis, anti-TNF exposure was associated with benefits for several clinically meaningful outcomes in children with enthesitis-related arthritis.</p>

<p><strong>BACKGROUND: </strong>Enthesitis-related arthritis (ERA) is a specific subtype of juvenile idiopathic arthritis (JIA) defined according to the International League of Associations for Rheumatology (ILAR) criteria. We aimed to characterize the clinical features and treatment regimens in an inception cohort of children with ERA.</p>

<p><strong>METHODS: </strong>We performed a retrospective, cross-sectional, multicenter cohort study including subjects diagnosed with ERA between 1989 and 2012. Patients all fulfilled the ILAR criteria for ERA within 3&nbsp;months of initial presentation to the rheumatology clinic. Differences in the prevalence of clinical criteria across study sites and by human leukocyte antigen (HLA)-B27 status were assessed using the Wilcoxon rank-sum or chi-square test, as appropriate.</p>

<p><strong>RESULTS: </strong>Two hundred thirty-four children met the inclusion criteria. Their median age at diagnosis was 11.6&nbsp;years, and 59% were HLA-B27-positive. Sixty-nine percent had enthesitis and arthritis at the time of diagnosis. Seventy-eight percent had a pauciarticular onset. The prevalence of all ILAR criteria at diagnosis, except arthritis and acute anterior uveitis, differed significantly across sites (all p &lt; 0.01). Medication use varied significantly across sites for children with peripheral arthritis (p &lt; 0.001), but not for sacroiliitis or enthesitis only. Nonsteroidal anti-inflammatory drugs and disease-modifying antirheumatic drugs were the most commonly prescribed treatments, with anti-TNF agents primarily being initiation for sacroiliitis. HLA-B27 positivity was associated with male sex, higher active joint count, sacroiliitis, and higher disease activity at disease onset.</p>

<p><strong>CONCLUSIONS: </strong>The majority of children had a pauciarticular onset, and several statistically significant clinical differences based on HLA-B27 status were identified. The observed heterogeneity in clinical presentation across sites reflects either true differences in patient populations or differences in how the ILAR criteria are being applied.</p>