Abstract
Background. Over the past decade, the OMERACT Myositis Working Group (MWG) conducted several focus groups and international consensus studies with adult idiopathic inflammatory myopathy (IIM) patients, and identified pain, fatigue and physical activity (later operationalized as physical function based on focus groups) as the most important domains to assess. There is a lack of reliable and valid patient-reported outcome measures (PROMs) assessing these domains that are also available in multiple languages. A systematic literature review and discussions with patient research partners resulted in identification of three Patient Reported Outcome Information System (PROMIS) scales assessing pain interference (6a v1.0), fatigue (7a v1.0) and physical function (8b v2.0) as candidate PROMs. The objective of this study was to evaluate the construct validity and test-retest reliability of the PROMIS pain interference, fatigue, and physical function forms in adult IIM.
Methods. PROMs were deployed to adult IIM patients (excluding inclusion body myositis) from the OMERACT MWG international clinic sites (Australia, Canada, the Netherlands, South Korea, Sweden, UK, USA). For construct validity, data was analyzed from the OMERACT MWG 2019 Survey of Content Validity and Feasibility and 2021 Survey of Construct Validity and Reliability. In addition to the three candidate PROMs, Functional Assessment of Chronic Illness Therapy-Fatigue, Pain Disability Index, International Physical Activity Questionnaire, Myositis Activities Profile, numeric pain rating scale, PROMIS anxiety (4a v1.0), depression, sleep disturbance, and social participation were obtained. For construct validity, a total of 14 a priori hypotheses were generated based on consensus (>75% agreement by MWG members). Pearson correlation was calculated to assess the correlations between instruments for each hypothesis. For test-retest reliability, PROMIS instruments were administered at time zero and 7 days later with numeric pain rating scale as anchor. Test-retest reliability was assessed using both Pearson correlation and intra-class correlation coefficient (ICC) (considered strong if ICC or r >0.75). Internal consistency was assessed using Cronbach-α (considered good if ≥0.8, and excellent if ≥0.9). Floor and ceiling effects were determined based on histograms of each instrument.
Results. Of 368 participants who received a survey link, 161 (44%) completed ≥1 PROM and 263 completed test-retest questionnaire. Average age of participants was 60 (SD 11) with 73% female: 80% were from USA (n=129), followed by Australia (n=8, 5%), the UK (n=7, 4%), Canada (n=5, 3%), the Netherlands (n=2, 1%), and Sweden (n=2, 1%). For construct validity, 11 out of 14 a priori hypotheses were met supporting construct validity of the three PROMIS instruments (3/5 for pain interference, 4/4 for fatigue, and 4/5 for physical function) (Figure). Test-retest reliability was strong for all three PROMIS instruments with ICCs (95%CI) of 0.93 (0.91-0.95) for pain interference, 0.94 (0.91-0.95) for fatigue, and 0.97 (0.96-0.98) for physical function. All three PROMIS instruments demonstrated good/excellent internal consistency with Cronbach-α ranging from 0.89 to 0.97. None of the measures demonstrated any ceiling or floor effects with the exception of a significant ceiling effect in the pain interference scale (31%).
Conclusions. This study provides reliability and validity evidence for application of the PROMIS pain interference (6a v1.0), fatigue (7a v1.0), and physical function (8b v2.0) instruments in a large international cohort of adult patients with IIM. Internal consistency of these instruments was good to excellent. Both fatigue and physical function instruments did not show any ceiling or floor effect supporting their ability to capture the full spectrum of constructs. However, significant ceiling effect noted in the pain interference instrument raises concern about its use in patients with minimal/no pain. Further longitudinal studies to assess the responsiveness of these measures are currently ongoing in multiple countries.