Objectives Juvenile systemic lupus erythematosus (JSLE) and juvenile dermatomyositis (JDM) are systemic autoimmune rheumatic diseases (RMDs) with childhood-onset associated with increased risk of damage accumulation and cardiovascular disease (CVD) over the life course.

Methods Damage associated with JSLE and JDM has been assessed using validated outcome measures in a longitudinal single-centre cohort study with long-term follow-up, involving data collected both retrospectively and prospectively. Descriptive statistics, sensitivity and regression analyses have been used to evaluate predictors of damage and CVD-risk.

Results We assessed comparatively a JSLE cohort (n=76), with a mean age of 24.3 ±4.2 years and a JDM cohort (n=79) with a mean 20.1 ± 5.0 years (p<0.001), with matched duration of follow-up (10.0 ± 4.2 vs. 11.0 ± 5.1, respectively, p=0.68). Traditional CVD-risk factors, including hypertension (p=0.02), dyslipidaemia (p=0.0005), and higher total cholesterol (p=0.01) and LDL-cholesterol (p=0.02) levels at the last assessment were higher in JSLE vs. JDM. Over the disease course, 39 (51.3%) AYA with JSLE vs. 47 (59.4%) AYA with JDM accumulated damage (p=0.307), which was independently predicted by the body mass index in both cohorts (p=0.038 and p=0.026, respectively).

The PDAY score was the only tool able to stratify AYA based on CVD-risk (median = 5 (4-13) points in JSLE vs. 0 (0-3) points in JDM, p=0.0001), as all the adult CVD-risk scores were very low in both cohorts.

Conclusions This is the first comparative evaluation of JSLE vs. JDM in adulthood, which highlighted increased damage burden and CVD-risk in JSLE that warrants further investigation.

Statement of clinical significance No previous studies explored log-term outcomes and cardiovascular risk assessment in juvenile systemic lupus erythematosus (JSLE) compared to juvenile dermatomyositis (JDM), despite both conditions sharing pathogenic mechanisms, a significant risk of organ damage, and overlapping therapeutic approaches. Additionally, there is a scarcity of studies following children and young people into adulthood and none evaluating the performance of validated cardiovascular disease (CVD)-risk scores in these two conditions. This study provides the first comparative evaluation of organ specific damage accrual and their predictors, and CVD-risk drivers in JSLE vs. JDM in two cohorts with similar mean disease duration of over 10 years. Our results highlight similar prevalence of overall damage in both conditions, but with distinct organ and systems involvement, and significantly increased CVD-risk in JSLE. Interestingly, in addition to recognised predictors, the body mass index (BMI) was an independent predictor of damage in both cohorts, which emphasizes the need for better strategies to address modifiable contributors to damage accrual. This study raises awareness that CVD-risk scores validated for use in adult populations underperform in both JSLE and JDM in young adulthood, highlighting in parallel the potential clinical utility of a paediatric CVD-risk score (the PDAY score) for risk stratification in JSLE, as well as the need for more robust CVD-risk tools for adequate risk identification and tailored management strategies in JSLE and JDM later in life.

The authors have declared no competing interest.

No specific funding has been received for this study. CC in supported by a National Institute of Heath Research (NIHR) University College London Hospital (UCLH) Biomedical Research Centre grant (BRC4/III/CC), a Versus Arthritis grant (22908) and a Lupus UK grant (CC/2025).

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All participants provided informed consent, and the study was approved by the London-Harrow Research Ethics Committee, reference 11/LO/0330.

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