Content Validity of Sjögren's Syndrome Symptom Diary and Functional Assessment of Chronic Illness Therapy-Fatigue in Patients with Sjögren's.

Introduction: Sjögren's Syndrome Symptom Diary (SSSD) and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) are patient-reported outcome (PRO) instruments assessing Sjögren's symptoms. Original SSSD items have demonstrated content validity, however qualitative evidence supporting the updated 'tiredness' item and two new supplementary items is lacking. Although well established and validated in other rheumatic diseases, there is no qualitative evidence supporting content validity of FACIT-F in Sjögren's. This study addressed these evidence gaps to support use of SSSD and FACIT-F as clinical trial endpoints, in clinical practice and in other research settings.

Methods: Qualitative, semi-structured telephone interviews were conducted with patients with Sjögren's (n = 12) and expert Sjögren's physicians (n = 10). Patient interviews explored content validity (e.g., understanding and relevance) of the new and updated SSSD items, perceptions of item and total score meaningful change on SSSD, and understanding and relevance of FACIT-F items. Physician interviews explored opinions on various SSSD scoring approaches.

Results: The new and updated SSSD items and FACIT-F demonstrated good content validity. Most patients considered a two-point improvement on most SSSD items meaningful, as well as a one- or two-point total score improvement. Most physicians reported tracking changes in patient responses to individual items as the most appropriate SSSD scoring approach.

Conclusions: SSSD and FACIT-F are content valid in a Sjögren's population, meeting an important criterion to support their use as clinical trial endpoints, but also their use in clinical practice and other research settings. Qualitative data exploring meaningful change will be valuable in supporting psychometrically derived responder definitions.