Background/Purpose:

The Lupus Severity Index (LSI)* was recently proposed to stratify patients by disease severity for clinical research. The LSI ranges from 0-10, is calculated using ACR classification criteria (ACRc) and demonstrated high predictive accuracy for severity anchored to major immunosuppressive drug use. We investigated the performance and characteristics of the LSI in a large multiethnic lupus cohort.

Methods:

Patients from a single academic center were followed from 1990-2016 using a custom database. Records of all SLE patients were abstracted. Variables included birthdate, diagnosis date, self-reported ethnicity, ACRc, SLICC Damage Index (SDI), treatment and date of death. Ethnicity was categorized into White (WHI), Asian (ASN), Indigenous (IND), and Other. The LSI was calculated from ACRc, and compared between ethnic groups and demographic variables known to be associated with severe SLE using t-tests, ANOVA, Pearson correlation coefficient and logistic regression.

Results:

Eight hundred thirty-two SLE patients were identified: 497 (60%) WHI; 220 (26%) IND; 91 (11%) ASN; 24(3%) Other. Mean age was 49±16 years, mean disease duration 15±11 years, 90% female, mean age at diagnosis 35±15; 163 (20%) of patients had died. The mean LSI was 6.9±1.7, range 3.2-9.7. The distribution of the LSI was similar to that in the original dataset (Fig 1A) and the area under the ROC curve, measured against prescription of major immunosuppressive drugs, was 0.69 (95%CI 0.65-0.73). LSI was higher in males compared to females (7.3±1.6 vs. 6.9±1.7; p-0.019), and was negatively associated with onset age (Onset<18yrs LSI=7.8±1.3; 18-50yrs LSI= 6.8±1.7; >50yrs LSI= 6.6±1.6; p<0.001)> LSI correlated with SDI(Pearson 0.28, p<0.001), and was a predictor of accruing any damage (SDI>1) (OR1.2 95% CI 1.1-1.3).LSI was higher in non-whites compared to whites: WHI LSI=6.6±1.7; IND LSI=7.2±1.6;Other LSI=7.3±1.3; ASN LSI 8.1±1.1; p<0.001).  LSI was a predictor of early mortality (Death at age<50, or disease duration<10 years): OR 1.2; 95%CI 1.0-1.3).  The distribution of the LSI varied by ethnic group with more uniformly severe disease in ASN patients (Figure 1B,C) compared to WHI and IND.

Conclusion:

Similar to the original publication, a higher LSI correlated with male sex, younger onset age, and non-white ethnicity; all groups shown to have more severe SLE. LSI was also a predictor of damage and early mortality. In addition we also found the distribution of LSI to differ between ethnicities. These findings confirm the utility of the LSI in stratifying patients by severity, and supports further exploration of the LSI to investigate contributors to severe SLE.

*Bello GA et al. Lupus Science & Medicine 2016