OBJECTIVE:To assess the 2022 American College of Rheumatology (ACR)/EULAR classification criteria for antineutrophil cytoplasmic antibody-associated vasculitis (AAV) in children with chronic small-to-medium vessel vasculitis. METHODS:A cohort of 574 patients, identified by physician's diagnosis (MD-diagnosis) in A Registry of Childhood Vasculitis, was classified by computation of registry data as having granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), or eosinophilic GPA after applying (1) ACR/EULAR AAV criteria and (2) pediatric-adapted European Medicines Agency (Ped-EMA) classification algorithm (incorporating Ankara GPA criteria). Venn diagrams compared the resulting GPA and MPA cohorts with MD-diagnosis. Sensitivity and specificity of criteria for GPA were evaluated against MD-diagnosis. Fisher exact test evaluated differences in the frequencies of individual clinical features in GPA versus MPA. RESULTS:Comparing ACR/EULAR criteria against the Ped-EMA algorithm for classifying AAV, more patients were classified as GPA or MPA (n = 396 vs 360, respectively), fewer had GPA (n = 261 vs 288, respectively), more had MPA (n = 135 vs 72, respectively), and fewer GPA cases coclassified as MPA (12% vs 28%, respectively); there were more differences between GPA and MPA in Pediatric Vasculitis Activity Score-defined clinical features (n = 14 vs 10, respectively). When classifying GPA by ACR/EULAR or Ankara criteria, sensitivity (74.5% vs 72.1%, respectively) was comparable, and specificity for ACR/EULAR criteria (93.9% vs 79.9%, respectively) was improved. CONCLUSION:The 2022 ACR/EULAR classification criteria for AAV perform at least as well as previous pediatric criteria and provide categorical MPA criteria where none existed previously; the criteria for GPA and MPA now specifically differentiate each other, with more differences between them in the frequencies of clinical features. Our findings support the preferential use of ACR/EULAR over Ankara criteria for GPA in pediatrics.

BackgroundProtein biomarkers such as interleukin 18 (IL-18), CXCL9, and the S100A alarmin proteins are increasingly used in the diagnosis and treatment of juvenile idiopathic arthritis (JIA) and Still's Disease (SD). Reported values for these biomarkers vary considerably among different testing platforms at different centers, representing a barrier to their clinical application as well as international research collaborations. We undertook a systematic evaluation of measurement comparability across different platforms in Europe (EU) and North America (NoA).MethodsRecombinant proteins including IL-18, CXCL9, S100A8/9, and S100A12 spiked into donor human serum were distributed in blinded fashion to participating centers in NoA and EU for determination of sample concentration on each center's measurement platform. Assay-specific mathematical correction formulas were calculated based on spike recovery data. Next, samples from the Childhood Arthritis and Rheumatology Research Alliance (CARRA) First-line Options for Systemic JIA Treatment (FROST) study were utilized for validation on selected platforms. Comparisons between measurement platforms before and after mathematical correction were analyzed.ResultsIn the spiked samples, while overall strong correlation was observed for IL-18 measurements across different platforms, the percent recovery revealed significant analytical variation ranging between approximately 50-400%. Similar variation in recovery was also observed for CXCL9, S100A8/9, and S100A12 across different measurement platforms. Analysis of real-world samples from the FROST study revealed strong correlation in IL-18 and CXCL9 values when comparing the same bead-based platforms at two different centers. Significant differences and systematic bias in measurement of FROST samples were uncovered when comparing ELISA or Ella platforms to commercial Luminex platforms. The application of regression-based mathematical correction factors generated from the spike recovery assays could only partly resolve these inter-platform differences.ConclusionsThis is the first systematic analysis of the comparability of biomarker measurements used in JIA and SD across different platforms including ELISA, Luminex, and Ella. We demonstrate substantial differences in the quantification of standardized biomarker concentrations both between assay types and across testing sites. In contrast, analyses of real-world samples from sJIA patients showed high concordance between two independent Ella platforms, indicating that this platform could improve clinical and research standardization.

OBJECTIVE:To assess associations of ancestry with juvenile idiopathic arthritis (JIA) categories and clinical Juvenile Arthritis Disease Activity Scores (cJADAS10) at presentation to pediatric rheumatology care in a multicultural country with universal health care. METHODS:Parents reported their child's ancestry in the Research in Arthritis in Canadian Children Emphasizing Outcomes (ReACCh-Out) cohort. For each ancestry reported for ≥30 children, we compared JIA category distribution and median cJADAS10 scores among three groups: only that ancestry, with that and other ancestries, and without that ancestry. Chi-square, Fisher's exact, and Kruskal-Wallis tests compared the three groups and multivariable linear regression assessed factors associated with cJADAS10 scores. RESULTS:Among 1,407 participants, 629 (44.7%) reported more than one ancestry. British ancestry was associated with higher median cJADAS10 scores (7.5) and higher frequency of enthesitis-related arthritis (18.7%) and psoriatic arthritis (10.0%), French ancestry was associated with lower cJADAS10 scores (5.8) and higher oligoarthritis (51.2%), Indigenous ancestry was associated with higher cJADAS10 scores (11.0) and higher rheumatoid factor-positive polyarthritis (21.9%), Black ancestry was associated with higher rheumatoid factor-positive polyarthritis (16.0%), and Eastern European ancestry was associated with lower cJADAS10 scores (3.6). Associations of ancestry with cJADAS10 scores were largely explained by differences in JIA categories (total R2 = 0.28, with R2 = 0.25 for JIA category alone). Black ancestry was associated with longer time from symptom onset to diagnosis (27 vs 18.9 weeks). CONCLUSIONS:British and French ancestries had distinct associations with JIA categories and cJADAS10 scores, and many children had multiple ancestries, questioning the use of a single "European" reference group. Higher cJADAS10 scores were largely explained by differences in JIA categories across ancestries.

OBJECTIVE:We aimed to study the disease course, outcomes, and predictors of outcome in pediatric-onset antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) affecting the kidneys. METHODS:Patients eligible for this study had a diagnosis of granulomatosis with polyangiitis (GPA), microscopic polyangiitis, or ANCA-positive pauci-immune glomerulonephritis, were 18 years or younger at diagnosis, had renal disease defined by biopsy or dialysis dependence, and had clinical data at diagnosis and at either 12 or 24 months. Ambispective data from A Registry for Children with Vasculitis/Pediatric Vasculitis Initiative Registry was used. The primary outcome was inactive renal disease (pediatric vasculitis activity score = 0 or 1) at 12 months. Secondary outcomes included rates of improved renal function and damage within 24 months. Renal function, defined by estimated glomerular filtration rate, was categorized into Kidney Disease Improving Global Outcomes (KDIGO) stages at diagnosis and tested as a predictor of outcome using a proportional-odds logistic regression model. RESULTS:A total of 145 patients were included: 68% were female, and 78% had GPA. At 12 months, 83% of patients achieved inactive renal disease; however, 42% had evidence of permanent renal damage. Compared with patients with normal renal function at diagnosis, patients with moderate to severely reduced renal function, or kidney failure at diagnosis, had an odds ratio of 8.62 (P = 0.002; 95% confidence interval [CI] 2.31-32.1) and 26.3 (P < 0.001; 95% CI 6.32-109), respectively, for being in a non-normal KDIGO category at 12 months. CONCLUSION:The majority of patients with pediatric AAV achieve inactive renal disease by 12 months; however, almost half have evidence of damage. Renal function at diagnosis is a strong predictor of renal function at 12 months.

Objectives To develop and validate classification criteria for paediatric chronic nonbacterial osteomyelitis (CNO) jointly supported by the European Alliance of Associations for Rheumatology (EULAR) and the American College of Rheumatology (ACR). Methods This international initiative had 4 phases: (1) candidate items were proposed in a survey of paediatric rheumatologists, (2) criteria definition and reduction by Delphi and nominal group technique exercises, (3) criteria weighting using multicriteria decision analysis, and (4) refinement of weights and threshold score in a development cohort of 441 patients and validation in another cohort of 514 patients. Results The new EULAR/ACR classification criteria for CNO require typical radiographic or magnetic resonance imaging findings and bone pain as an obligatory entry criterion and exclusion criteria of malignancy, infection, vitamin C deficiency, and hypophosphatasia, followed by additive weighted criteria in 5 clinical (site of bone lesions, pattern of bone lesions, age at onset, coexisting conditions, fever) and 4 pathology/laboratory domains (bone biopsy findings if done, anaemia, C-reactive protein level, and erythrocyte sedimentation rate). A total score ≥55 is required for classification as CNO. The new criteria had a sensitivity of 82% and specificity of 98% in the validation cohort. Conclusions These new classification criteria for paediatric CNO developed with international input reflect current views about CNO, have high specificity and good sensitivity, and provide a key foundation for future CNO research.

OBJECTIVE:To develop and validate classification criteria for pediatric chronic nonbacterial osteomyelitis (CNO) jointly supported by EULAR and the American College of Rheumatology (ACR). METHODS:This international initiative had 4 phases: (1) candidate items were proposed in a survey of pediatric rheumatologists, (2) criteria definition and reduction by Delphi and nominal group technique exercises, (3) criteria weighting using multicriteria decision analysis, and (4) refinement of weights and threshold score in a development cohort of 441 patients and validation in another cohort of 514 patients. RESULTS:The new EULAR/ACR classification criteria for CNO require typical radiographic or magnetic resonance imaging findings and bone pain as an obligatory entry criterion and exclusion criteria of malignancy, infection, vitamin C deficiency, and hypophosphatasia, followed by additive weighted criteria in 5 clinical (site of bone lesions, pattern of bone lesions, age at onset, coexisting conditions, fever) and 4 pathology/laboratory domains (bone biopsy findings if done, anemia, C-reactive protein level, and erythrocyte sedimentation rate). A total score ≥55 is required for classification as CNO. The new criteria had a sensitivity of 82% and specificity of 98% in the validation cohort. CONCLUSION:These new classification criteria for pediatric CNO developed with international input reflect current views about CNO, have high specificity and good sensitivity, and provide a key foundation for future CNO research.

Chronic primary systemic vasculitis (PSV) comprises a group of heterogeneous diseases that are broadly classified by affected blood vessel size, clinical traits and the presence (or absence) of anti-neutrophil cytoplasmic antibodies (ANCA) against proteinase 3 (PR3) and myeloperoxidase (MPO). In small vessel vasculitis (SVV), ANCA are not present in all patients, and they are rarely detected in patients with vasculitis involving medium (MVV) and large (LVV) blood vessels. Some studies have demonstrated that lysosome-associated membrane protein-2 (LAMP-2/CD107b) is a target of ANCA in SVV, but its presence and prognostic value in childhood MVV and LVV is not known. This study utilized retrospective sera and clinical data obtained from 90 children and adolescents with chronic PSV affecting small (SVV, n = 53), medium (MVV, n = 16), and large (LVV, n = 21) blood vessels. LAMP-2-ANCA were measured in time-of-diagnosis sera using a custom electrochemiluminescence assay. The threshold for seropositivity was established in a comparator cohort of patients with systemic autoinflammatory disease. The proportion of LAMP-2-ANCA-seropositive individuals and sera concentrations of LAMP-2-ANCA were assessed for associations with overall and organ-specific disease activity at diagnosis and one-year follow up. This study demonstrated a greater time-of-diagnosis prevalence and sera concentration of LAMP-2-ANCA in MVV (52.9% seropositive) and LVV (76.2%) compared to SVV (45.3%). Further, LAMP-2-ANCA-seropositive individuals had significantly lower overall, but not organ-specific, disease activity at diagnosis. This did not, however, result in a greater reduction in disease activity or the likelihood of achieving inactive disease one-year after diagnosis. The results of this study demonstrate particularly high prevalence and concentration of LAMP-2-ANCA in chronic PSV that affects large blood vessels and is seronegative for traditional ANCA. Our findings invite reconsideration of roles for autoantigens other than MPO and PR3 in pediatric vasculitis, particularly in medium- and large-sized blood vessels.

OBJECTIVE:Granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) are chronic life-threatening vasculitides requiring substantial immunotherapy. Adult trials identified rituximab (RTX) as an alternative to cyclophosphamide (CYC) for remission induction of GPA and MPA. Disease rarity has limited feasibility of similar trials with pediatric patients. We aim to evaluate the relative efficacy and toxicity of CYC and RTX for patients with childhood GPA and MPA through registry-based comparative evaluation. METHODS:From A Registry of Childhood Vasculitis, we identified patients with GPA and MPA who received induction with RTX or CYC. Pediatric Vasculitis Activity Score (PVAS) and Pediatric Vasculitis Damage Index (pVDI) score evaluated disease activity and damage. Descriptive statistics summarized patient characteristics. RTX and CYC comparisons used logistic regression for primary outcomes of postinduction remission (PVAS = 0) or low disease activity (PVAS ≤ 2). Hospital admission for adverse events and pVDI scores were compared using logistic regression and ordinal regression, respectively. RESULTS:Among 104 patients, 43% received RTX, 46% CYC, 11% both. Treatment groups did not significantly differ for diagnosis PVAS and onset age. There was no difference in remission among the groups (63% overall; odds ratio [OR] 1.07, 95% confidence interval [CI] 0.45-2.52). Hospitalizations occurred in 22% of patients receiving RTX versus 10% patients receiving CYC (OR 2.27, 95% CI 0.73-7.05). The median 12-month pVDI score was 1 in both groups (OR 0.98, 95% CI 0.43-2.22). CONCLUSION:This is the first study comparing CYC and RTX for induction in pediatric GPA and MPA. No significant differences were shown in rates of remission, severe adverse events, or organ damage. Limitations included lack of standardized treatment regimens, retrospectivity, and lack of longitudinal adverse drug-related event data.

Purpose In this 6-year study we identified factors associated with spontaneous vertebral body reshaping in glucocorticoid (GC)-treated children with leukemia, rheumatic disorders, and nephrotic syndrome. Methods Subjects were 79 children (mean age 7.4 years) who had vertebral fracture (VF) evaluation on lateral spine radiographs at least 1 year after VF detection. VF were graded using the modified Genant semiquantitative method and fracture burden for individuals was quantified using the spinal deformity index (SDI; sum of grades from T4 to L4). Results Sixty-five children (82.3%) underwent complete vertebral body reshaping (median time from VF detection to complete reshaping 1.3 years by Cox proportional hazard modeling). Of 237 VF, the majority (83.1%) ultimately reshaped, with 87.2% reshaping in the thoracic region vs 70.7% in the lumbar region (P = .004). Cox models showed that (1) every g/m2 increase in GC exposure in the first year after VF detection was associated with a 19% decline in the probability of reshaping; (2) each unit increase in the SDI at the time of VF detection was associated with a 19% decline in the probability of reshaping [hazard ratio (HR) = 0.81; 95% confidence interval (CI) = 0.71, 0.92; P = .001]; (3) each additional VF present at the time of VF detection reduced reshaping by 25% (HR = 0.75; 95% CI = 0.62, 0.90; P = .002); and (4) each higher grade of VF severity decreased reshaping by 65% (HR = 0.35; 95% CI = 0.21, 0.57; P < .001). Conclusion After experiencing a VF, children with higher GC exposure, higher SDI, more severe fractures, or lumbar VF were at increased risk for persistent vertebral deformity.

OBJECTIVE:Using Canadian Alliance of Pediatric Rheumatology Investigators (CAPRI) juvenile idiopathic arthritis (JIA) registry data, we describe (1) clinical characteristics of patients with JIA transitioning to adult care, (2) prevalence of disease-related damage and complications, and (3) changes in disease activity during the final year prior to transfer.METHODS:Registry participants who turned 17 years between February 2017 and November 2021 were included. Clinical characteristics and patient-reported outcomes (PROs) at the last recorded pediatric rheumatology visit, and changes observed in the year prior to that visit were analyzed. Physicians completed an additional questionnaire characterizing cumulative disease-related damage and adverse events by age 17 years.RESULTS:At their last visit, 88 of 131 participants (67%) had inactive and 42 (32%) had active disease. Overall, 96 (73%) were on medications and 41 (31%) were on biologic disease-modifying antirheumatic drugs. Among 80 participants for whom the additional questionnaire was completed, 26% had clinically detected joint damage, 31% had joint damage on imaging, 14% had uveitis, and 7.5% had experienced at least 1 serious adverse event. During the final year, 44.2% of patients were in remission, 28.4% attained inactive disease, and 27.4% became or remained active. Mean scores of PROs were stable overall during that last year, but a minority reported marked worsening.CONCLUSION:A substantial proportion of youth with JIA transitioning to adult care in Canada had a high disease burden, which was reflected by their degree of disease activity, joint damage, or ongoing medication use. These results will inform pediatric and adult providers of anticipated needs during transition of care.

Objectives The objective of this study is to evaluate whether anti-neutrophil cytoplasmic antibody (ANCA) seropositivity and antigen specificity at diagnosis have predictive utility in paediatric-onset small vessel vasculitis.Methods Children and adolescents with small vessel vasculitis (n=406) stratified according to the absence (n=41) or presence of ANCA for myeloperoxidase (MPO) (n=129) and proteinase-3 (PR3) (n=236) were compared for overall and kidney-specific disease activity at diagnosis and outcomes between 1 and 2 years using retrospective clinical data from the ARChiVe/Paediatric Vasculitis Initiative registry to fit generalised linear models.Results Overall disease activity at diagnosis was higher in PR3-ANCA and MPO-ANCA-seropositive individuals compared with ANCA-negative vasculitis. By 1 year, there were no significant differences, based on ANCA positivity or specificity, in the likelihood of achieving inactive disease (~68%), experiencing improvement (≥87%) or acquiring damage (~58%). Similarly, and in contrast to adult-onset ANCA-associated vasculitis, there were no significant differences in the likelihood of having a relapse (~11%) between 1 and 2 years after diagnosis. Relative to PR3-ANCA, MPO-ANCA seropositivity was associated with a higher likelihood of kidney involvement (OR 2.4, 95% CI 1.3 to 4.7, p=0.008) and severe kidney dysfunction (Kidney Disease Improving Global Outcomes (KDIGO) stages 4–5; OR 6.04, 95% CI 2.77 to 13.57, p<0.001) at onset. Nonetheless, MPO-ANCA seropositive individuals were more likely to demonstrate improvement in kidney function (improved KDIGO category) within 1 year of diagnosis than PR3-ANCA seropositive individuals with similarly severe kidney disease at onset (p<0.001).Conclusions The results of this study suggest important paediatric-specific differences in the predictive value of ANCA compared with adult patients that should be considered when making treatment decisions in this population.