Sit to stand and timed up and go in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies can significantly impair physical function, of which Sit to Stand (STS) and Timed Up and Go (TUG) are quick, operator independent measures. We aimed to evaluate psychometric properties of STS and TUG compared to established core set measures of disease activity; and assess feasibility of patients self-performing these tests remotely. Data from a 6-month prospective observational study (Myositis Patient Centered Tele-Research Study -My PACER) was analyzed. Patient-reported and functional assessments were collected monthly over 6 months. A total of 120 patients (75% female, 81% White, mean age 55.5 ± 13.4 years,52% Dermatomyositis, 39% Polymyositis, 9% Necrotizing Myopathy) participated. There was strong test-retest reliability between baseline and month one for STS (r = 0.80) and TUG (r = 0.87); p < 0.01. At baseline, STS and TUG showed a very strong correlation with each other (r = - 0.75) and with most CSMs. Strong correlations were seen with Muscle Disease Activity and a validated Patient Reported Outcome measure of physical function, PROMIS-PF 20. At 6 months, STS and TUG were significantly better among patients who improved according to Total Improvement Score. STS and TUG showed good reliability, even when self-performed remotely using video instructions, with excellent construct validity and responsiveness.