Comparison of ESSDAI and ClinESSDAI in potential optimisation of trial outcomes in primary Sjögren’s syndrome: examination of data from the UK Primary Sjögren’s Syndrome Registry

Objectives: To assess the use of the Clinical EULAR Sjögren’s Syndrome Disease Activity Index (ClinESSDAI), a version of the ESSDAI without the biological domain, in terms of potential eligibility and outcomes for clinical trials in patients with primary Sjögren’s syndrome (pSS), according to the new ACR-EULAR classification criteria, from the UK Primary Sjögren’s Syndrome Registry (UKPSSR). Methods: 665 patients from the UKPSSR cohort were analysed at their time of inclusion in the registry. ESSDAI and ClinESSDAI were calculated for each patient. Results: For different disease activity indexes cut-off values, more potentially eligible participants were seen using ClinESSDAI than ESSDAI. The distribution of patients according to defined disease activity levels does not differ statistically (Chi2 P = 0.57) between ESSDAI and ClinESSDAI for moderate disease activity (score ≥5 <14; ESSDAI: 36.4%; ClinESSDAI: 36.5%) or high disease activity (score ≥14; ESSDAI: 5.4%; ClinESSDAI: 6.8%). We didn’t find significant differences in terms of activity levels for individual domains between the indexes with the exception of the articular domain. We found a good level of agreement between both indexes and a positive correlation between lymphadenopathy and glandular domains with the use of both indexes for different cut-off values. With the use of ClinESSDAI, the minimal clinically important improvement value is more often achievable with a one grade improvement of a single domain than with the use of ESSDAI. We observed similar results when using the new ACR-EULAR classification criteria or the previously used American-European Consensus Group (AECG) classification criteria for pSS. Conclusions: In the UKPSSR population, the use of ClinESSDAI instead of ESSDAI does not lead to significant changes in score distribution, potential eligibility or outcome measurement in trials, or in routine care when immunological tests are not available. These results need to be confirmed in other cohorts and with longitudinal data.