Construct Validity of the Adult Myopathy Assessment Tool in Individuals with Inclusion Body Myositis

Michael Harris-Love¹, Galen Joe², Todd Davenport³, Joseph Shrader², Beverly McElroy⁴, Goran Rakocevic⁵, Olavo Vasconcelos⁶ and Marinos Dalakas⁵, ¹Geriatrics Service, VA Medical Ctr, Washington, DC, ²Rehabilitation Medicine Department, National Institutes of Health, Bethesda, MD, ³Department of Physical Therapy, University of the Pacific, Stockton, CA, ⁴National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, ⁵Department of Neurology, Thomas Jefferson University, Philadelphia, PA, ⁶Department of Neurology, Richmond Veterans Affairs Medical Center, Richmond, VA

Meeting: 2014 ACR/ARHP Annual Meeting

Keywords: Assessment, Fatigue, myopathy, myositis and strength

Session Information

Title: Rehabilitation Sciences (ARHP)

Session Type: Abstract Submissions (ARHP)

Background/Purpose

The Adult Myopathy Assessment Tool (AMAT) is a 13-item performance-based battery developed to assess function and anaerobic endurance in adults with muscle disease. The AMAT has been shown to be a valid assessment of physical status in people with neuromuscular disease, and has demonstrated intrarater and interrater reliability among clinicians rating patients with idiopathic inflammatory myopathy. The purpose of this study was to determine the construct validity of the AMAT in patients with sporadic inclusion body myositis (sIBM).

Methods

The AMAT was administered to 43 participants with sIBM (31 men, 12 women; age: 66.0 ±7.5 years; disease duration: 9.9 ±4.3 years) by a single practitioner at a Federal hospital. Peak isometric force measurements were obtained using quantitative muscle testing, and temporal characteristics of gait during habitual and fast walking conditions were measured using a portable gait analysis system. The participants also completed assessments for depression (Beck Depression Inventory), psychosocial fatigue (Fatigue Severity Scale), physical activity levels (Human Activity Profile), and self-reported physical status (36-item Short Form Health Survey, Ver. 2, Physical Component Summary).

Results

The participants attained a mean AMAT score of 30.1 (±5.7; range, 18-44). AMAT scores were significantly associated with strength (r = 0.40-0.43, p < 0.01), gait speed (r = 0.69-0.73, p < 0.001), physical activity levels (r = 0.67, p < 0.001) and self-reported physical status (r = 0.50, p < 0.005), but not depression or psychosocial fatigue (p > 0.05). These relationships were independent of age, disease duration, and age of onset. No floor or ceiling effects were observed as no participant attained the minimum or maximum score (0-45).

Conclusion

The construct validity of the AMAT is supported by its significant associations with muscle strength, functional performance, physical activity, and self-reported physical status. However, anaerobic endurance as measured by the AMAT differs from estimates of psychosocial fatigue in our sample. The AMAT is a standardized, performance-based tool that may be used to assess functional limitations and anaerobic endurance in patients with sIBM.

Disclosure:

M. Harris-Love,
None;

G. Joe,
None;

T. Davenport,
None;

J. Shrader,
None;

B. McElroy,
None;

G. Rakocevic,
None;

O. Vasconcelos,
None;

M. Dalakas,
None.

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