Background The Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SLICC/ACR DI) is associated with increased healthcare cost and mortality. We compared the trajectory of total and individual damage items of the SLICC/ACR DI in African-American vs Caucasian ethnicities in a large prospective SLE cohort. We calculated the attributable risk of comorbidities and socioeconomic factors.
Methods Poisson regression was used to calculate the rate of damage per year for each organ. Cox regression modeling was used to determine the association between time to the individual damage item and ethnicity. Pooled logistic regression models of prospective data were used to calculate the population attributable risk (PAR) for each damage organ.
Results We included 2,436 patients: 43% African-American, 57% Caucasian, and 92% female. There was a linear relationship between time since diagnosis and mean SLICC/ACR DI score, with no plateau. Compared to Caucasians, African-Americans had a faster total, renal, pulmonary, and skin damage accrual rate. Hypertension contributed to 30% of total damage, 70% of renal and 40% of cardiovascular damage. The three socioeconomic measures (education, income, and insurance) accounted for only about 10% of any organ damage and contributed approximately equally to total damage.
Conclusions The linear increase in damage in both ethnicities over time is of particular concern. Ethnicity and hypertension are both important contributors to organ damage in SLE, but socioeconomic factors play a lesser role.
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