Objective: To evaluate the responsiveness of the EULAR Sjögren's Syndrome Patient Reported Index (ESSPRI) and EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI) in patients with primary Sjögren's syndrome (pSS) treated with rituximab.
Methods: Twenty-eight patients with pSS treated with rituximab (1000 mg) infusions on days 1 and 15 were included in the study. Data were collected prospectively at baseline and 16, 24, 36, 48 and 60 weeks after treatment. Internal responsiveness was assessed using standardised response means (SRM) and effect sizes (ES). SRM and ES <0.5, 0.5-0.8 and >0.8 were interpreted as small, moderate and large, respectively. External responsiveness was assessed using Spearman correlation coefficients.
Results: Median (range) ESSPRI and ESSDAI scores at baseline were 6.7 (0.3-9.0) and 8 (2-18), respectively. Both indices improved significantly after treatment. SRM and ES values for ESSPRI and ESSDAI were ≥0.8 at week 16 and decreased afterwards, and were larger for ESSDAI than for ESSPRI. SRM and ES values for patient's and physician's global disease activity (GDA) and rheumatoid factor broadly followed the pattern of those of ESSPRI and ESSDAI. SRM and ES for stimulated whole salivary flow were small at all time points. At baseline and for most change scores, moderate to good correlations were found between ESSPRI and patient's GDA and between ESSDAI and physician's GDA. Poor association was found between ESSPRI and ESSDAI.
Conclusions: ESSPRI and ESSDAI are sensitive measures of change in disease activity after therapeutic intervention, which supports the usefulness of these indices for future clinical trials in patients with pSS. The responsiveness of ESSDAI was greater than that of ESSPRI.