Validation of two simple patient-centered outcome measures for virtual monitoring of patients with idiopathic inflammatory myositis

BACKGROUND: Telemedicine has changed the landscape of patient care with wider use of patient-centered outcome measures (PCOMs). We evaluated two novel task–based PCOMs namely ten times arm lift (AL) test and two-minute walk distance (2MWD) in idiopathic myositis (IIM). METHODS: This was a cross-sectional observational study with the enrolment of adult IIM (ACR/EULAR criteria) patients with active/inactive disease. Active disease was defined as any two of increase in immunosuppression within 3 months, elevated muscle enzymes, physician VAS ≥ 2, worsened cutaneous disease, or fall in MMT8 < 76. Standard myositis core set measures (CSMs) were evaluated and test–retest validity [Cronbach’s alfa (CA)], construct validity (Pearson’s correlation), and discriminant validity (between active/inactive IIM) were assessed. The results were further validated in a separate tele-rheumatology cohort. RESULTS: Among 22 IIM patients (68%-female) of age 30.5(19–62) years, AL and 2MWD showed excellent test–retest reliability (CA-0.987, 0.99). AL exhibited moderate-strong correlation with all CSMs except CK levels and MDI. In contrast, 2MWD values were highly variable without CSM correlation. A higher AL time discriminated active and inactive myositis (16.6 vs 11 s, p = 0.006) with an AUC of 0.882 (p = 0.006). AL > 12.8 s had 94% negative predictive value (NPV) for active muscle disease. In the validation cohort (47 patient visits among 26 patients), AL significantly differentiated between active vs. inactive disease with an NPV of 95%. CONCLUSIONS: AL test exhibits pilot evidence of construct and discriminant validity in patients with IIM requiring further evaluation. 2MWD was not a good test for outcome evaluation of IIM patients. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10067-021-05990-3.