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Functional Index-3: A Valid and Reliable Functional Outcome Assessment Measure in Patients With Dermatomyositis and
Floranne C Ernste1, Christopher Chong2, Cynthia S Crowson3
1F.C. Ernste, MD, Division of Rheumatology, Department of Medicine, Mayo Clinic, Rochester, Minnesota, USA; ernste.floranne@mayo.edu.
The Journal of Rheumatology
|April 17, 2020
Summary
The Functional Index-3 (FI-3) effectively assesses muscle endurance in dermatomyositis (DM) and polymyositis (PM) patients. This new tool demonstrates strong validity and reliability for clinical use.
Area of Science:
- Rheumatology
- Clinical Assessment
- Musculoskeletal Disorders
Background:
- Patients with dermatomyositis (DM) and polymyositis (PM) often experience reduced muscle endurance, impacting their quality of life.
- Existing assessment tools may require optimization for efficient and accurate measurement of this key symptom.
Purpose of the Study:
- To streamline the Functional Index-2 (FI-2) by developing the Functional Index-3 (FI-3).
- To evaluate the measurement properties, content validity, construct validity, and reliability of the newly developed FI-3 for assessing muscle endurance in DM and PM patients.
Main Methods:
- The FI-2 dataset (n=63) was analyzed for redundancy, and its content was revised to create FI-3.
- Construct validity and intrarater reliability of FI-3 were tested in 43 DM/PM patients across two centers.
- Interrater reliability was assessed in 25 patients, with construct validity compared against MAP, HAQ, and Borg CR-10 using Spearman correlation.
Main Results:
- Spearman correlation coefficients showed moderate to high correlations between FI-3 tasks (shoulder/hip flexion) and MAP/HAQ scores.
- Lower correlations were observed for neck flexion tasks and very low to moderate correlations with the Borg scale.
- Intraclass correlation coefficients (ICC) indicated moderate to good intrarater reliability (0.88-0.98) and fair to good interrater reliability (0.83-0.96) for FI-3 tasks.
Conclusions:
- The Functional Index-3 (FI-3) is an efficient and valid clinical tool for assessing muscle endurance in DM and PM patients.
- The construct validity of FI-3 is supported by significant correlations with established measures like MAP, HAQ, and Borg CR-10, confirming its clinical utility.
