Background Little is known about the economic burden of NP lupus. We estimated direct and indirect costs (DC, IC) associated with NP events attributed to SLE and non-SLE causes using multistate modelling.
Methods Patients fulfilling ACR classification criteria for SLE from 31 centres in 11 countries were enrolled within 15 months of diagnosis. NP events were documented annually using ACR NP definitions and attributed to SLE or non-SLE causes. At each assessment and for SLE and non-SLE events, patients were stratified into 1 of 3 NP states (no, resolved, or new/ongoing NP event). The change in NP status characterized by transition rates between states was analyzed using multistate modelling (doi:10.1002/art.41876).
At each assessment, annual DC and IC were based on health resource use and lost work-force/non-work-force productivity over the preceding year. Resource use was costed using 2021 Canadian prices and lost productivity using Statistics Canada age-and-sex specific wages. Costs associated with SLE and non-SLE NP states were calculated by averaging all observations in each NP state. Multiple regressions adjusted for possible confounding of age at diagnosis, sex, race/ethnicity, disease duration, geographic region, education, and smoking on the association of annual DC and IC and NP state. 5 and 10-year cumulative costs for NP states were predicted by multiplying adjusted annual costs for each state by the expected state duration, forecasted using multistate modelling.
Results 1697 patients (89% female, 51% non-Caucasian race/ethnicity, mean age at enrolment 35.1 years) were followed a mean of 8.8 years. 1971 NP events occurred in 956 patients, 32% attributed to SLE. For SLE NP events, annual DC were higher in those with new/ongoing vs no events ($10,809 vs $6715) (table 1). Annual and 5-yr IC were higher in new/ongoing vs no events and new/ongoing vs resolved events (5-yr: new/ongoing vs no: $172,674 vs $136,970). For non-SLE NP events, annual IC were higher in new/ongoing vs no events, new/ongoing vs resolved events, and resolved vs no events and 5 and 10-yr IC were higher in new/ongoing vs no events (10-yr: new/ongoing vs no: $342,434 vs $279,874). For all NP states, IC exceeded DC 2.8 to 4-fold.
Conclusion IC are 1.3-fold higher in patients with new/ongoing vs no NP events. While DC trended higher in new/ongoing events, they were not significantly higher across all NP states and times. Impaired productivity associated with ongoing and resolved NP lupus is substantial, contributing to the previously documented reduced quality of life.
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