Clinical Meaningfulness and Improvement Thresholds of Myositis Core Set Measures: Association with Patient-Reported Outcomes

Abstract

Objective The study aimed to evaluate the clinical meaningfulness and improvement thresholds of the myositis core set measures (CSMs) of disease activity in idiopathic inflammatory myopathies (IIM), emphasizing associations with patient-reported outcome measures (PROMs). Methods Adults with IIM were enrolled in a six-month prospective observational study. PROMs were collected monthly, including patient global assessments, health assessment questionnaire (HAQ), pain and fatigue (VAS), Short Form-36, and PROMIS-Physical Function. Physician-reported outcomes (physician global assessment, extra-muscular disease activity [ExGLB], manual muscle testing [MMT]), and total improvement score (TIS) of 2016 ACR/EULAR Myositis Response Criteria were collected every 3 months. Associations were evaluated using Spearman correlation and linear mixed models to assess construct validity. Responsiveness, effect sizes, and clinically important differences (CIDs) were assessed using the anchors patient- and physician-global impression of change (PtGIC and PhGIC) at 6 months. Results Fifty patients (mean age 51.6 [SD 14.9] years; 60% females) were enrolled. Most CSMs showed strong baseline and longitudinal associations with PROMs, including pain, fatigue, physical function, and quality of life (QoL). Significant improvements were observed in most CSMs with moderate to large effect sizes, using PtGIC and PhGIC as anchors. The CIDs according to PtGIC were 2.1 for physician global disease activity, 1.4 for ExGLB, 1.7 for patient global disease activity, 4.3 for MMT, 0.5 for HAQ, 1475 IU/L for CK, and 28 for TIS. PhGIC demonstrated similar results. Conclusion CSMs demonstrate robust validity and responsiveness, closely aligning with patients' symptoms, function, and QoL, supporting their utility in IIM trials. We established CIDs for CSMs and TIS.