Background/Purpose: Myositis leads to significant morbidity and loss of function. Currently, simple objective measures of patient functional outcomes are lacking.  Our aims were to a) test functional measures (sit to stand [STS], timed up and go [TUG], and 6-minute walk distance [6MWD]) in myositis patients against established myositis core set measures, and b) evaluate reliability of the same measures self-performed by patients at home.

Methods: We collected data on the 6 validated myositis core measures (manual muscle testing [MMT], physician global disease activity, patient global disease activity, extra-muscular global disease activity, HAQ and muscle enzymes) as well as performed 3 functional measures in clinic (STS, TUG, and 6MWD) on patients with DM, PM and necrotizing myopathy at baseline, 3 and 6 months. STS is number of times a patient can stand from a seated position and sit back down, as many times in 30 seconds. TUG is the time needed to rise from a chair, walk 3 meters, return to the chair and sit down. 6MWD is the maximum distance patient can walk in 6 minutes. We instructed patients on conducting these functional measures at home, and they reported performance results at home within a week of clinic evaluation. To assess validity we compared functional measures against all core set measures at baseline and MMT longitudinally. We examined test-retest reliability of home assessments with in clinic assessments. We use Spearman correlations with rho >0.5 considered strong, 0.35-0.5 moderate, and 0.2-0.35 weak.

Results: Data from 31 patients [58% females, 90% Caucasians, mean age 48 (±16)] from an ongoing observational study were included in this analysis. As shown in table 1, at baseline, STS correlated strongly with  MMT, patient/physician global assessment, and muscle enzymes, and had moderate correlation with HAQ, and no correlation with extra-muscular global.  Similarly, at baseline, TUG showed moderate correlation with physician/patient global and muscle enzymes, but only weak association with MMT, HAQ and extra-muscular global. The 6MWD showed strong correlation with MMT, moderate with patient global and HAQ, and weak with physician global and muscle enzymes. Longitudinally, 6MWD showed strong association with MMT, where as STS and TUG showed moderate and weak associations with MMT respectively. Home assessments of STS (rho: 0.91), TUG (rho: 0.94) and 6MWD (rho: 0.86) showed high test-retest reliability compared to clinic assessment (P<0.01 for all 3).

Conclusion: Preliminary data suggests strong cross sectional correlation of STS and 6MWD with MMT and moderate to strong correlation with MMT longitudinally. All tests were reliable when self-performed by patients at home. This suggests these simple measures may provide objective functional assessment of patient-centric outcomes in myositis in clinic as well as  at home.