Clinical Phenotype, Treatment Exposure, Treat-to-Target Status, and Longitudinal Outcomes in Juvenile-Onset Systemic Lupus Erythematosus: A Single-Center Retrospective Cohort Study

Background/Objectives: Juvenile-onset systemic lupus erythematosus (jSLE) is a multisystem disease requiring disease control, glucocorticoid minimization, and treat-to-target assessment. We characterized phenotype, treatment exposure, childhood lupus low disease activity state (cLLDAS), and outcomes. Methods: This retrospective cohort included 54 patients followed during 2020–2025. One patient who died 10 days after diagnosis contributed to baseline and cumulative analyses but not longitudinal or last-visit analyses (n=53); all survivors had ≥6 months of follow-up. Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) and Paediatric Rheumatology European Society (PReS)-endorsed cLLDAS were assessed; paired changes were analyzed with the Wilcoxon signed-rank test. Results: Forty-three patients (79.6%) were female; median age at diagnosis was 15.0 years and median follow-up among survivors was 34.6 months. Cumulative hematologic and mucocutaneous involvement occurred in 64.8% and 61.1%, respectively. Biopsy-proven lupus nephritis occurred in 29.6%, with class IV in 13/16 cases (81.3%). Hydroxychloroquine was used in 53/54 (98.1%), and oral prednisolone in 46/54 (85.2%) for a median 17.5 months. Median SLEDAI-2K decreased from 8.0 to 4.0 (p< 0.001); anti-double-stranded DNA antibody (anti-dsDNA), complement C3, and spot urine protein-to-creatinine ratio improved significantly. At last follow-up, 29/53 (54.7%) fulfilled cLLDAS. Flare, infection-related hospitalization, intensive care unit (ICU) admission, and mortality occurred in 22.2%, 20.4%, 5.6%, and 1.9%, respectively. Conclusions: Disease activity and serological and renal markers improved, and just over half achieved cLLDAS, although residual disease activity and infection-related morbidity remained relevant.