Background: The SIMPLE (SIMple Disease Assessment for People with Lupus Erythematosus) index is a composite numeric tool that captures disease activity from patients’ self-assessment with minimal physicians’ input. The SIMPLE index consists of 2 components: patient self-reported survey questionnaire (3 items from the lupus symptoms domain from the validated LupusPRO, 10 items from Lupus Impact Tracker [LIT], change in the health status and current glucocorticoids use [and dose]) and two laboratory tests (low complements [C3/C4] and urine protein-creatinine ratio >0.5). The values are put in an equation to derive a number, which is transformed to a 0- to 100-point scale by a formula using weighted scores of the above parameters. The SIMPLE index has been validated in US with good correlation with physicians’ assessment of disease activity.

Objectives: To validate the SIMPLE index for systemic lupus erythematosus (SLE) disease activity assessment in a longitudinal cohort of Chinese patients.

Methods: Adult patients (age ≥18 years) who fulfilled the 2012 SLICC criteria for SLE and were followed in the Rheumatology clinics of Tuen Mun Hospital, Hong Kong were recruited. Patients were followed for a total of 3 consecutive visits, including hospitalization. Participants were invited to complete the SIMPLE questionnaire before seeing doctors on the same day of clinic visit or hospital stay. The two laboratory results were supplemented by research nurses. Physicians, who were blinded to the SIMPLE results, were asked to complete disease activity assessment by the SELENA-SLEDAI and physicians’ global assessment (PGA) after consultation. Correlation was made between the SIMPLE score and the SLEDAI/PGA scores by Spearman’s rank correlation test. Correlation was also performed for the changes in total/clinical SLEDAI, PGA with the change in SIMPLE index during subsequent visits relative to baseline.

Results: 399 SLE patients were studied (93.7% women; age 45.3±13.4 years; disease duration 13.3±8.0 years). The proportion of patients having a history of neuropsychiatric and renal disease that required immunosuppressive therapies was 9.8% and 55.6%, respectively. At visit 1, 18 (4.5%) patients had clinical SLEDAI ≥5 and 98 (24.6%) had clinical SLEDAI 1-4. The mean total SLEDAI was 3.02±2.87 and PGA score was 0.60±0.53. A total of 178 patients (44.6%) had SDI score ≥1. The mean SIMPLE index was 25.6±12.8. SIMPLE index correlated significantly with clinical SLEDAI (ρ=0.56; p<0.001), total SLEDAI (ρ=0.75; p<0.001) and PGA score (ρ=0.41; p<0.001). At visit 3, 87 and 38 patients, respectively, had a drop in total SLEDAI score by ≥1 and ≥4, and the corresponding change in SIMPLE index was 35.3±13.7 to 25.0±10.1 (p<0.001) and 42.9±11.9 to 26.0±11.1 (p<0.001). Conversely, 103 and 29 patients, respectively, had an increase in total SLEDAI score by ≥1 and ≥4. The corresponding increase in SIMPLE index was 23.5±11.3 to 25.7±10.1 (p=0.007) and 25.3±13.7 to 27.3±11.6 (p=0.27). Change in SIMPLE index from visit 1 to 3 correlated significantly with the change in total SLEDAI (ρ=0.35; p<0.001), clinical SLEDAI (ρ=0.19; p<0.001) and PGA (ρ=0.14; p=0.005). ROC analysis performed with pooled data from all the 3 visits showed that a SIMPLE index of >24 points best predicted a clinical SLEDAI score of 1-4 (area under the curve [AUC] 0.72[0.68-0.75]; sensitivity 0.65; specificity 0.64), and >31 points best predicted a clinical SLEDAI score of ≥5 (AUC 0.84[0.77-0.91]; sensitivity 0.76, specificity 0.81).

Conclusion: The SIMPLE index shows a good correlation with SELENA-SLEDAI and PGA. It is also sensitive to change in SLEDAI and PGA score during subsequent visits. The SIMPLE index is a simple tool that enables patients to self-report disease activity and communicate with the health care team more efficiently.

Disclosure of Interests: None declared