Measurement properties of the Inclusion Body Myositis Functional Rating Scale.

To evaluate the validity, reliability, responsiveness and meaningful change threshold of the Inclusion Body Myositis (IBM) Functional Rating Scale (FRS). Data from a large 20-month multicentre, randomised, double-blind, placebo-controlled trial in IBM were used. Convergent validity was tested using Spearman correlation with other health outcomes. Discriminant (known groups) validity was assessed using standardised effect sizes (SES). Internal consistency was tested using Cronbach's alpha. Intrarater reliability in stable patients and equivalence of face-to-face and telephone administration were tested using intraclass correlation coefficients (ICCs) and Bland-Altman plots. Responsiveness was assessed using a standardised response mean (SRM). An receiver operator characteristic (ROC) curve anchor-based approach was used to determine clinically meaningful IBMFRS change. Among the 150 patients, mean (SD) IBMFRS total score was 27.4 (4.6). Convergent validity was supported by medium to large correlations (r When administered by trained raters, the IBMFRS is a reliable, valid and responsive tool that can be used to evaluate the impact of IBM and its treatment on physical function, with a 2-point reduction representing meaningful decline. NCT02753530.

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Competing interests: SS is supported by a UCL Queen Square Institute of Neurology & Cleveland Clinic London MPhil/PhD Neuroscience Fellowship. TS, HD, SR, JR, LL-P and SH are employees of Clinical Outcomes Solutions, a health research consultancy that was paid to conduct the measurement properties analyses reported in this study. CG was an employee of Orphazyme A/S, the pharmaceutical company that funded the measurement properties analyses reported in this study. LH has no disclosures to report. RJB has received funding from the FDA Office Orphan Products Development grant for his role in the arimoclomol trial. MGH receives research funding from the Medical Research Council UK and has previously acted as a consultant for Novartis and for Orphazyme A/S. MMD serves or recently served as a consultant for Abata/Third Rock, Abcuro, Amicus, ArgenX, Astellas, Cabaletta Bio, Catalyst, CNSA, Covance/Labcorp, CSL-Behring, Dianthus, Horizon, EMD Serono/Merck, Ig Society, Janssen, Medlink, Octapharma, Priovant, Sanofi Genzyme, Shire Takeda, TACT/Treat NMD, UCB Biopharma, Valenza Bio and Wolters Kluwer Health/UpToDate; MMD also received research grants or contracts or educational grants from Alexion/AstraZeneca, Alnylam Pharmaceuticals, Amicus, Argenx, Bristol-Myers Squibb, Catalyst, CSL-Behring, FDA/OOPD, GlaxoSmithKline, Genentech, Grifols, Mitsubishi Tanabe Pharma, MDA, NIH, Novartis, Octapharma, Orphazyme, Ra Pharma/UCB, Sanofi Genzyme, Sarepta Therapeutics, Shire Takeda, Spark Therapeutics, The Myositis Association, and UCB Biopharma/RaPharma. PMM has received honoraria from Abbvie, BMS, Celgene, Eli Lilly, Galapagos, Janssen, MSD, Novartis, Orphazyme Pfizer, Roche and UCB.