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Research ArticleMyositis

Functional Index-3: A Valid and Reliable Functional Outcome Assessment Measure in Patients With Dermatomyositis and Polymyositis

Floranne C. Ernste, Christopher Chong, Cynthia S. Crowson, Tanaz A. Kermani, Orla Ni Mhuircheartaigh and Helene Alexanderson
The Journal of Rheumatology January 2021, 48 (1) 94-100; DOI: https://doi.org/10.3899/jrheum.191374
Floranne C. Ernste
1F.C. Ernste, MD, Division of Rheumatology, Department of Medicine, Mayo Clinic, Rochester, Minnesota, USA;
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  • ORCID record for Floranne C. Ernste
  • For correspondence: ernste.floranne@mayo.edu
Christopher Chong
2C. Chong, MD, Arthritis Associates and Osteoporosis Center of Colorado Springs, Colorado Springs, Colorado, USA;
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Cynthia S. Crowson
3C.S. Crowson, PhD, Department of Health Science Research, Division of Biostatistics, Mayo Clinic, Rochester, Minnesota, USA;
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Tanaz A. Kermani
4T.A. Kermani, MD, University of California at Los Angeles, California, USA;
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Orla Ni Mhuircheartaigh
5O. Ni Mhuircheartaigh, MBBCh, Division of Rheumatology, Department of Medicine, Beacon Hospital, Dublin, Ireland;
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Helene Alexanderson
6H. Alexanderson, PhD, Department of Neurobiology, Care Science and Society, Division of Physiotherapy, and Department of Medicine, Division of Rheumatology Karolinska Institutet, and Function Area Occupational Therapy and Physical Therapy, Karolinska University Hospital, Solna, Stockholm, Sweden.
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Abstract

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.

Key Indexing Terms:
  • idiopathic inflammatory myopathies
  • Functional Index-2
  • muscle endurance
  • outcome measures
  • Accepted for publication March 27, 2020.
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1 Jan 2021
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Functional Index-3: A Valid and Reliable Functional Outcome Assessment Measure in Patients With Dermatomyositis and Polymyositis
Floranne C. Ernste, Christopher Chong, Cynthia S. Crowson, Tanaz A. Kermani, Orla Ni Mhuircheartaigh, Helene Alexanderson
The Journal of Rheumatology Jan 2021, 48 (1) 94-100; DOI: 10.3899/jrheum.191374

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Functional Index-3: A Valid and Reliable Functional Outcome Assessment Measure in Patients With Dermatomyositis and Polymyositis
Floranne C. Ernste, Christopher Chong, Cynthia S. Crowson, Tanaz A. Kermani, Orla Ni Mhuircheartaigh, Helene Alexanderson
The Journal of Rheumatology Jan 2021, 48 (1) 94-100; DOI: 10.3899/jrheum.191374
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Keywords

IDIOPATHIC INFLAMMATORY MYOPATHIES
Functional Index-2
muscle endurance
OUTCOME MEASURES

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Keywords

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  • muscle endurance
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