Renal involvement in different subtypes of children with juvenile idiopathic arthritis: results from a single-center cohort.
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BACKGROUND: Renal involvement in juvenile idiopathic arthritis (JIA) is uncommon (observed in 8.5% of our cohort) and may arise from either the disease itself or its medications. However, differences in renal manifestations across JIA subtypes remain poorly characterized. OBJECTIVE: To investigate the prevalence, risk factors, and prognostic implications of renal involvement, and to characterize the nature of renal manifestations across JIA subtypes. METHODS: A retrospective cohort study was conducted involving 376 JIA patients treated from May 2015 to May 2022. Data on medications, laboratory findings, subtypes, and disease activity were analyzed. RESULTS: Renal involvement rates by subtype were as follows: systemic JIA (SJIA, 16.2%), rheumatoid factor (RF)-positive polyarticular JIA (9.5%), enthesitis-related arthritis (ERA, 8.5%), oligoarticular JIA (OJIA, 6.3%), and RF-negative polyarticular JIA (3.4%). SJIA patients with renal involvement all had proteinuria and high serum amyloid A levels. All non-systemic JIA patients had hematuria (two with proteinuria). Only polyarticular JIA patients with renal involvement showed elevated interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) levels. In contrast, ERA and OJIA patients had no IL-6/TNF-α changes, regardless of renal involvement. ERA cases also had elevated serum IgA. Cox regression analysis revealed that elevated C-reactive protein (HR 1.039, p < 0.001), higher Juvenile Arthritis Disease Activity Score in 27 joints (HR 1.160, p < 0.001), and longer duration of active disease (HR 1.052, p = 0.008) independently predicted renal involvement, whereas biologics were protective (HR 0.394, p = 0.043). All patients were followed up for at least 24 months. At final follow-up, renal involvement resolved in 81.3% of JIA patients, including all SJIA and OJIA cases, but only 25% of RF-positive polyarticular JIA patients. CONCLUSIONS: This study provides preliminary evidence of distinct patterns of renal involvement across JIA subtypes. The findings support the hypothesis that controlling active disease is important for renal outcomes. Future studies are needed to validate these subtype-specific mechanisms. Key Points • Renal involvement occurred in 8.5% of JIA patients, strongly associated with disease activity. • In SJIA with renal involvement, proteinuria is commonly observed and may be associated with amyloidosis. • ERA patients with renal involvement often present with hematuria, possibly due to IgA nephropathy. • RF-positive polyarticular JIA with renal involvement demonstrates elevated IL-6/TNF-α. Anti-CCP positivity predicts poorer outcomes, mandating intensified renal surveillance and aggressive inflammation control.