ESSDAI activity index of the SJÖGRENSER cohort: analysis and comparison with other European cohorts.

The objective of the study was to assess the ESSDAI index characteristics in the SJÖGRENSER cohort (Spanish Rheumatology Association's registry of patients with Primary Sjögren Syndrome [PSS]). SJÖGRENSER is a prospective multicentric study on a cohort of Spanish patients with PSS who meet the 2002 American-European consensus from rheumatology units. 298 variables were studied in patients for the inclusion of the study from an anonymous list from each department. The ESSDAI (EULAR Sjögren's syndrome disease activity index) includes 12 domains and measures systematic activity in PSS patients. Each domain is divided into 3-4 levels, (0: no activity; 1: low activity; 2: moderate activity; 3: high activity) and is attributed a weight. Each domain score is obtained by multiplying the activity level by the weight assigned. According to ESSDAI: low activity < 5; moderate activity 5-13, and high activity ≥ 14. ESSDAI was compared between several European PSS cohorts (EULAR, ASSES, GEAS, GRISS, Ducth). 437 patients were included from 33 Spanish rheumatology units. 95.2% were women with a median age of 58.63 years [p25-p75: 50.02-67.98 years] and average PSS evolution of 10.4 years (6-16 years). ESSDAI median on entering the study was 2 (0-4). 31% of patients had ESSDAI 0; low activity 49%, moderate activity 15%, and high activity 5%. Those with greater activity were the joint, haematological and biological domains, whereas the lung was the most affected organ with pleural and parenchymatous involvement. Unlike other European cohorts, the initial SJÖGRENSER cohort was characterised by low-zero systemic activity in 80% of patients, which differentiates it from other cohorts and provides a prospective study opportunity.