Outcome measures for primary Sjögren's syndrome: a comprehensive review

Lymphocytic infiltration of different exocrine and non-exocrine epithelia is the pathological hallmark of primary Sjögren's syndrome, whereas involvement of salivary and lachrymal glands with the clinical counterpart of dry eye and dry mouth are the predominant features of the disease, together with fatigue and musculoskeletal pain. In addition, systemic manifestations, like arthritis, skin vasculitis, peripheral neuropathy, glomerulonephritis, may also be present in a consistent number of patients. As result, clinical features in SS can be divided into two facets: the benign subjective but disabling manifestations such as dryness, pain and fatigue, and the systemic manifestations. In the past decades, great efforts have been made to develop valid tools for the assessment of these both facets. Disease specific questionnaires such as Profile of Fatigue and Discomfort (PROFAD) and Sicca Symptom Inventory (SSI) have been proposed for evaluation of patients' symptoms, whereas different composite indexes have been suggested for the assessment of systemic disease activity. After that, an international project supported by EULAR, emerged to develop consensus disease activity indexes: the EULAR Sjögren's Syndrome Patients Reported Index (ESSPRI), and the EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI), a systemic activity index to assess systemic manifestations. Both EULAR indexes have been developed in an international collaboration to be consensual. Both indices have now been validated in a large independent international cohort. They both have been shown to be feasible, valid and reliable instruments. Also, we have found that these two scores did not correlate, suggesting that these two indexes assess two different disease components that poorly overlap, but were complementary. The sensitivity to change of both scores has been assessed, they are both able to detect change, however, ESSDAI score, like other systemic score, is more sensitive to change than ESSPRI and other patient scores. Current work is ongoing to define disease activity levels and clinically important changes for defining significant clinical improvement with the systemic score ESSDAI, and ESSPRI. We hope that this increased knowledge on the way to assess patients with primary SS, along with the emergence of new targeted therapy, will put a great input in the improvement of conduction of clinical trials in pSS.