The Functional Index-3 in Adult Dermatomyositis and Polymyositis: Validity and Reliability of an Outcome Measure for Muscle Endurance

Christopher Chong¹, Orla Ni Mhuircheartaigh¹, Helene Alexanderson², Tanaz A. Kermani³, Cynthia S. Crowson⁴, Abigail B. Green⁴, Ann M. Reed⁵ and Floranne C. Ernste⁶, ¹Internal Medicine, Mayo Clinic, Rochester, MN, ²Dept of Neuroscience, Care Science and Society, Karolinska Institutet, Stockholm, Sweden, ³Rheumatology, University of California Los Angeles, Los Angeles, CA, ⁴Department of Health Sciences Research, Mayo Clinic, Rochester, MN, ⁵Rheumatology, Mayo Clinic, Rochester, MN, ⁶Division of Rheumatology, Mayo Clinic Rochester, Rochester, MN

Meeting: 2012 ACR/ARHP Annual Meeting

Keywords: Myositis

Session Information

Title: Muscle Biology, Myositis and Myopathies: Classification, Treatment and Outcome in Idiopathic Inflammatory Myopathies

Session Type: Abstract Submissions (ACR)

Background/Purpose: Although muscle fatigue is a major source of functional impairment in dermatomyositis (DM) and polymyositis (PM), few valid and reliable methods for efficient evaluation of functional disability exist. The Functional Index (FI) was the first to specifically assess impairment in myositis, and consisted of 14 tasks to determine muscle endurance. The Functional Index-2 (FI-2) was a revision of FI, which decreased the tasks from 14 to 7. However, busy clinical practices may preclude feasibility of use. We developed a Functional Index-3 (FI-3) to streamline content for assessment of muscle endurance in DM and PM patients and tested its validity at a single, large academic center. Methods: Twenty-eight patients with DM or PM diagnosis were recruited at our institution from 2010-2012. All patients participated in at least one of two sessions which included 3 tasks (shoulder flexion, head lift, hip flexion) performed bilaterally. After each task, participants completed the Borg CR-10 to rate perceived muscle exertion. Self-reported limitations in daily activities were assessed by the Myositis Activity Profile (MAP) and the Health Assessments Questionnaire (HAQ). Intra-class correlation (ICC) coefficients were calculated. Performance results from the tasks were correlated to the MAP, HAQ, and Borg CR-10 using Spearman’s correlation coefficient to assess validity. Results: Fifteen patients with DM, 7 patients with anti-synthetase syndrome, and 6 patients with PM participated. The mean (SD) age was 58 (11) years and mean (SD) disease duration was 6.5 (5.4) years. There were 19 (68%) females. Six patients (21%) had active disease as determined by creatine kinase level and clinician judgment. Twelve patients completed the second session for intra-rater reliability. Consistently high ICC values indicate high intra-rater reliability: ICC (95% confidence interval): shoulder flexion, right 0.90 (0.69, 0.97); shoulder flexion, left 0.88 (0.64, 0.96); head lift, 0.66 (0.19, 0.89); hip flexion, right 0.64 (0.15, 0.88); hip flexion, left 0.84 (0.56, 0.95). Ten patients completed the second session for inter-rater reliability, and the high ICC values show that the raters agreed: shoulder flexion, right 0.81 (0.43, 0.95); shoulder flexion, left 0.94 (0.78, 0.98); head lift, 0.92 (0.74, 0.98); hip flexion, right 0.46 (-0.16, 0.83); hip flexion, left 0.60 (0.03, 0.88). Two patients had large decreases in repetitions in hip flexion during the second session (>8 repetitions). Correlations were significant between MAP, HAQ, and Borg CR-10 in all tasks as shown in the table. Conclusion: The FI-3 is an efficient and valid method for assessment of muscle endurance in DM and PM patients. FI-3’s validity is supported by the significant correlations between functional tasks and the MAP, HAQ, and Borg CR-10 scores.

Table. Spearman correlations of disease activity and Borg CR-10 scores with FI-3 task scores in session one

	MAP score (n=28)		HAQ score (n=27)		Borg CR-10 scores (n=28)
	correlation	p-value	correlation	p-value	correlation	p-value
Shoulder flexion right	-0.62	<0.001	-0.69	<0.001	-0.57	0.002
Shoulder flexion left	-0.54	0.003	-0.54	0.003	-0.45	0.016
Head lift	-0.50	0.006	-0.55	0.003	-0.38	0.046
Hip flexion right	-0.69	<0.001	-0.77	<0.001	-0.46	0.015
Hip flexion left	-0.56	0.002	-0.65	<0.001	-0.40	0.036

Disclosure:

C. Chong,
None;

O. Ni Mhuircheartaigh,
None;

H. Alexanderson,
None;

T. A. Kermani,
None;

C. S. Crowson,
None;

A. B. Green,
None;

A. M. Reed,
None;

F. C. Ernste,
None.

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