Reliability of the adult myopathy assessment tool in individuals with myositis

Abstract

Objective: The Adult Myopathy Assessment Tool (AMAT) is a 13-item performance-based battery developed to assess functional status and muscle endurance. The purpose of this study was to determine the intrarater and interrater reliability of the AMAT in adults with myositis.

Methods: Nineteen raters (13 physical therapists and 6 physicians) scored videotaped recordings of patients with myositis performing the AMAT for a total of 114 tests and 1,482 item observations per session. Raters rescored the AMAT test and item observations during a followup session (mean ± SD 19 ± 6 days between scoring sessions). All raters completed a single, self-directed, electronic training module prior to the initial scoring session.

Results: Intrarater and interrater reliability correlation coefficients were ≥0.94 for the AMAT functional subscale, endurance subscale, and total score (all P < 0.02 for Ho , ρ ≤0.75). All AMAT items had satisfactory intrarater agreement (kappa statistics with Fleiss-Cohen weights, with values κw = 0.57-1.00). Interrater agreement was acceptable for each AMAT item (κ = 0.56-0.89) except the sit up (κ = 0.16). The standard error of measurement and 95% confidence interval range for the AMAT total scores did not exceed 2 points across all observations (AMAT total score range 0-45).

Conclusion: The AMAT is a reliable, domain-specific assessment of functional status and muscle endurance for adult subjects with myositis. Results of this study suggest that physicians and physical therapists may reliably score the AMAT following a single training session. The AMAT functional subscale, endurance subscale, and total score exhibit interrater and intrarater reliability suitable for clinical and research use.

Trial registration: ClinicalTrials.gov NCT00030212.

Copyright © 2015 by the American College of Rheumatology.

Figures

Figure 1. Application of the Enablement-Disablement model and the ICF taxonomy to the Adult Myositis Assessment Tool subscales

The Adult Myositis Assessment Tool (AMAT) Subscales are organized in a domain-specific format that may be integrated into the World Health Organization (WHO) International Classification of Functioning, Disability and Health (ICF) taxonomy and the Institute of Medicine (IOM) Enablement-Disablement model. The AMAT incorporates two domains of disablement, impairment and functional limitation, to provide a theoretical basis for the subscale dichotomy. These subscales may be further described using the ICF classification codes which characterize the tasks within the context of the biopsychosocial model of functioning and disability.