RT Journal Article
SR Electronic
T1 Functional Index-3: A Valid and Reliable Functional Outcome Assessment Measure in Patients With Dermatomyositis and Polymyositis
JF The Journal of Rheumatology
JO J Rheumatol
FD The Journal of Rheumatology
SP 94
OP 100
DO 10.3899/jrheum.191374
VO 48
IS 1
A1 Floranne C. Ernste
A1 Christopher Chong
A1 Cynthia S. Crowson
A1 Tanaz A. Kermani
A1 Orla Ni Mhuircheartaigh
A1 Helene Alexanderson
YR 2021
UL http://www.jrheum.org/content/48/1/94.abstract
AB Objective. Patients with dermatomyositis (DM) and polymyositis (PM) have reduced muscle endurance.The aim of this study was to streamline the Functional Index-2 (FI-2) by developing the Functional Index-3 (FI-3) and to evaluate its measurement properties, content and construct validity, and intra- and interrater reliability.Methods. A dataset of the previously performed and validated FI-2 (n = 63) was analyzed for internal redundancy, floor, and ceiling effects. The content of the FI-2 was revised into the FI-3. Construct validity and intrarater reliability of FI-3 were tested on 43 DM and PM patients at 2 rheumatology centers. Interrater reliability was tested in 25 patients. The construct validity was compared with the Myositis Activities Profile (MAP), Health Assessment Questionnaire (HAQ), and Borg CR-10 using Spearman correlation coefficient.Results. Spearman correlation coefficients of 63 patients performing FI-3 revealed moderate to high correlations between shoulder flexion and hip flexion tasks and similar correlations with MAP and HAQ scores; there were lower correlations for neck flexion task. All FI-3 tasks had very low to moderate correlations with the Borg scale. Intraclass correlation coefficients (ICC) of FI-3 tasks for intrarater reliability (n = 25) were moderate to good (0.88–0.98). ICC of FI-3 tasks for interrater reliability (n = 17) were fair to good (range 0.83–0.96).Conclusion. The FI-3 is an efficient and valid method for clinically assessing muscle endurance in DM and PM patients. FI-3 construct validity is supported by the significant correlations between functional tasks and the MAP, HAQ, and Borg CR-10 scores.