Background/Purpose: ANCA associated vasculitis (AAV) is a chronic autoimmune disorder characterized by ANCA production and small vessel inflammation and necrosis. ANCA autoantigen targets include myeloperoxidase (MPO-ANCA) and proteinase 3 (PR3-ANCA). There is growing evidence that ANCA specificity may be more predictive of prognosis and outcome than clinical phenotype. Due to the scarcity of data in pediatric patients with AAV, treatment and prognosis are largely extrapolated from literature based on adult data. With a large, single-center inception cohort of pediatric AAV patients, this study aims to characterize the clinical characteristics and outcomes by ANCA specificity.

Methods: Our cohort included 88 pediatric patients ≤18 years of age at AAV diagnosis. Patients with AAV were diagnosed between 1985 and 2021 and according to the Chapel Hill Consensus Conference definitions. MPO-ANCA and PR3-ANCA were determined by enzyme-linked immunosorbent assay (ELISA). Clinical outcomes of interest were end stage renal disease (ESRD) defined as a need for renal replacement therapy, death, relapse, and remission. Baseline characteristics at presentation and treatment were analyzed with respect to the outcome. Continuous variables and categorical variables were compared using t test and Fisher’s exact test, respectively. Additionally, Kaplan-Meier survival curves were constructed for ESRD, relapse according to clinical diagnosis, and death. P-value < 0.05 was considered statistically significant. All analyses were done using SAS statistical software (SAS Institute, Inc., Cary, North Carolina).

Results: In our cohort, 36 patients (41%) were MPO-ANCA and 31 patients (35%) PR3-ANCA positive. Pediatric patients with MPO-ANCA vasculitis were younger at diagnosis with a median age of 13.5 years compared to 15 years for those with PR3-ANCA vasculitis. Regarding clinical diagnosis, microscopic polyangiitis (MPA) was most common at 67% among MPO-ANCA positive patients, and granulomatosis with polyangiitis (GPA) was most common at 62% among PR3-ANCA positive patients (p < 0.05). All renal limited patients were MPO-ANCA positive. A significantly higher proportion of MPO-ANCA positive patients had renal involvement (97% vs. 81%, p < 0.05), and PR3-ANCA positivity was associated with sinus (71% vs. 28%, p < 0.05) and skin manifestations (45% vs. 20%, p < 0.05) (Figure 1). In terms of induction treatments, PR3-ANCA and MPO-ANCA patients were similar. Methylprednisolone was used in 61% of PR3-ANCA and 72% of MPO-ANCA patients. Cyclophosphamide was used in 89% of PR3-ANCA and 72% of MPO-ANCA patients, and rituximab was used in 29% of PR3-ANCA and 24% of MPO-ANCA patients. Among the entire cohort, 33% of pediatric AAV patients reached ESRD, and MPO-ANCA positivity was associated with worse renal outcomes in the first 5 years after diagnosis (Figure 2).

Conclusion: In this large, single-center cohort of pediatric AAV patients, MPO-ANCA positivity was associated with younger age at onset, MPA phenotype, and renal-limited disease. Similar to previously published cohorts, a significant proportion of pediatric AAV reached ESRD, and MPO-ANCA positivity was also associated with worse renal outcomes in the first 5 years after diagnosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/clinical-characteristics-and-outcomes-of-pediatric-anca-associated-vasculitis-patients-single-center-inception-cohort/