Assessing Function and Endurance in Adults with Spinal and Bulbar Muscular Atrophy: Validity of the Adult Myopathy Assessment Tool

Michael O Harris-Love,Ellen Levy,Nicholas A Di Prospero,Angela Kokkinis,Galen Joe,Todd E Davenport,Joseph A Shrader,Kenneth H Fischbeck,Alison La Pean Kirschner,Sungyoung Auh,Cheunju Chen,Li Li,Lindsay Fernandez-Rhodes

doi:10.1155/2014/873872

Abstract

Purpose. The adult myopathy assessment tool (AMAT) is a performance-based battery comprised of functional and endurance subscales that can be completed in approximately 30 minutes without the use of specialized equipment. The purpose of this study was to determine the construct validity and internal consistency of the AMAT with a sample of adults with spinal and bulbar muscular atrophy (SBMA). Methods. AMAT validity was assessed in 56-male participants with genetically confirmed SBMA (mean age, 53 ± 10 years). The participants completed the AMAT and assessments for disease status, strength, and functional status. Results. Lower AMAT scores were associated with longer disease duration (r = −0.29; P < 0.03) and lower serum androgen levels (r = 0.49–0.59; P < 0.001). The AMAT was significantly correlated with strength and functional status (r = 0.82–0.88; P < 0.001). The domains of the AMAT exhibited good internal consistency (Cronbach's α = 0.77–0.89; P < 0.001). Conclusions. The AMAT is a standardized, performance-based tool that may be used to assess functional limitations and muscle endurance. The AMAT has good internal consistency, and the construct validity of the AMAT is supported by its significant associations with hormonal, strength, and functional characteristics of adults with SBMA. This trial is registered with Clinicaltrials.gov identifier NCT00303446.

Highlights

The adult myopathy assessment tool is a standardized, observed, physical performance test designed to be administered relatively quickly in clinical and research settings with common clinical equipment and minimal training
The functional and endurance domains that comprise the adult myopathy assessment tool (AMAT) reflect the contribution of impaired muscle force on functional limitations [1,2,3,4] and incorporate recent findings that physical performance in people with and without myopathy are affected by excessive fatigue [5, 6]
The maximal voluntary contraction (MVC) forces represented by the scaled total quantitative muscle assessment (QMA) score, scaled upper extremity (UE) QMA score, and scaled lower extremity (LE) QMA score were 42% to 65% of the reference values (Table 1)

Summary

Introduction

The adult myopathy assessment tool is a standardized, observed, physical performance test designed to be administered relatively quickly in clinical and research settings with common clinical equipment and minimal training (see Table 6 for the list of the AMAT tasks and scoring criteria). A strict functional assessment battery based on the attainment of a transfer or mobility task may exhibit a significant ceiling effect (more than 15% of subjects attain the maximum score) if patients have muscle force above what is needed to complete the task for a single repetition Impairments in these individuals could be revealed during a more demanding endurance task. An endurance battery may display a significant floor effect (more than 15% of subjects attain the minimum score) if patients do not have adequate muscle capacity to meet the criteria for a sustained or repetitive task [16] These same individuals may demonstrate the requisite strength to complete a single repetition of a less demanding functional task.

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