Development and Validation of the Inclusion Body Myositis-Health Index: A Disease-Specific Patient-Reported Outcome...

As novel therapeutic interventions are considered for individuals with inclusion body myositis (IBM), valid outcome measures are needed to quantify therapeutic gain and disease progression during clinical trials. To meet this need, we developed and validated the Inclusion Body Myositis-Health Index (IBM-HI), a regulatory-grade, disease-specific, patient-reported outcome measure capable of measuring a patient's perception of their point-in-time disease burden.

We conducted an international cross-sectional study where we asked participants with IBM about the most prevalent and impactful symptoms affecting their everyday lives. Symptoms identified in the cross-sectional survey were included in the first version of the IBM-HI. We subsequently used factor analysis, beta testing, test-retest reliability, and known groups analysis to validate, refine, and optimize the instrument.

Five hundred and sixty-nine individuals with IBM completed a survey to identify what issues and symptoms are most important to include and measure in an IBM-specific outcome measure. Fifteen individuals with IBM beta tested the first version of the IBM-HI and 21 participants completed test-retest reliability testing at baseline and two weeks. Participants found the IBM-HI to be easy to use, comprehensive, and highly relevant to their condition. Each of the IBM-HI questions and all 13 subscales were found to be reliable over a 14-day period (intraclass correlation coefficient = 0.95). Known groups assessments determined that the IBM-HI and its subscales are able to differentiate between predefined clinical and demographic subgroups expected to experience higher or lower levels of disease burden.

The IBM-HI is a reliable comprehensive instrument capable of measuring a wide spectrum of symptoms experienced by individuals with IBM. This instrument adds to existing IBM clinical trial infrastructure and provides clinicians and researchers with a mechanism to quantify how patients feel and function in the context of a therapeutic trial.