Field testing and clinical validation of the mSQUASH to measure physical activity in patients with Sjögren's disease.

Objectives: Regular physical activity is recommended in patients with rheumatic diseases. In order to uniformly measure physical activity, our aim was to perform field testing of the modified Short QUestionnaire to ASsess Health enhancing physical activity (mSQUASH) in Sjögren's disease (SjD), together with other rheumatic diseases, and to investigate construct validity and test-retest reliability of the mSQUASH in patients with SjD.

Methods: The mSQUASH was tested by conducting semi-structured interviews in patients with SjD (n=10), systemic lupus erythematosus (n=10), giant cell arteritis/polymyalgia rheumatica (n=10) and axial spondyloarthritis (n=13) to check for understandability, interpretation and relevance. For construct validity (n=263 SjD), the association of mSQUASH to other patient-reported outcome measures was analysed using Spearman correlations. It was hypothesised that correlations are highest for physical-related outcomes, with fair to moderate correlations due to partly overlapping constructs. For test-retest reliability (n=75 SjD), intra-class correlation coefficients (ICCs) were calculated and Bland-Altman analysis was performed.

Results: All patient groups perceived the mSQUASH as relevant and easy to complete. Some minor adaptations and clarifications were implemented. As expected, mSQUASH total score showed fair associations with ESSPRI total score (ρ=-0.30) and EQ-5D total score (ρ=-0.34). Within the subdomains, correlations were higher for ESSPRI fatigue and pain compared to dryness and highest for EQ-5D activity and mobility. Test-retest reliability was good, with an ICC of 0.84. Bland-Altman analysis showed no systemic bias, but limits of agreement were wide.

Conclusions: The mSQUASH is a feasible, valid and reliable questionnaire to assess daily physical activity in SjD patients.