Prediction of Organ Damage Accrual in Systemic Lupus Erythematosus Using a Frailty Index

Abstract

Background/Purpose: We previously constructed a frailty index (FI) as a measure of susceptibility to adverse outcomes among patients with systemic lupus erythematosus (SLE). In this work, higher baseline FI values were associated with increased mortality risk during follow-up. However, the association with other clinically important health outcomes has not been described. Therefore, the objective of the current study was to estimate the association of baseline FI values with the risk of subsequent organ damage accrual in a large, prospective, international, inception cohort of SLE patients.

Methods: Patients fulfilling ≥ 4 ACR classification criteria for SLE were recruited within 15 months of diagnosis and were assessed annually for medication use, comorbidities, disease activity (SLEDAI-2K), organ damage [SLICC/ACR Damage Index (SDI)], health-related quality of life [Short-Form 36 (SF-36)], and other measures.

For our analysis, the baseline visit was defined as the first at which both SDI and SF-36 data were available as both instruments, in addition to other variables, were used to generate the baseline FI scores. We determined organ damage accrual during follow-up by subtracting the baseline SDI score from the SDI score at the final study visit. Any change in SDI ≥ 1 defined damage accrual.

Multivariable negative binomial regression was used to estimate the association between baseline FI values and the rate of change in SDI scores per patient-year of follow-up, adjusting for relevant demographic and clinical characteristics. Model fit was evaluated using likelihood ratio (LR) tests and Akaike information criterion (AIC) values.

Results: The 1,549 SLE patients (84.8% of the cohort) eligible for this analysis were mostly female (88.7%) with mean (SD) age 35.7 (13.3) years and median (IQR) disease duration 1.2 (0.9-1.5) years at baseline. Mean (SD) baseline FI score was 0.17 (0.08) with a range from 0 to 0.51.