Patient reported outcomes in GNE myopathy: incorporating a valid assessment of physical function in a rare disease

Abstract

Background: The aim of this analysis was to evaluate the psychometric properties of three patient reported outcome (PRO) measures characterizing physical function in GNE myopathy: the Human Activity Profile, the Inclusion Body Myositis Functional Rating Scale, and the Activities-specific Balance Confidence scale.

Methods: This analysis used data from 35 GNE myopathy subjects participating in a natural history study. For construct validity, correlational and known-group analyses were between the PROs and physical assessments. Reliability of the PROs between baseline and 6 months was evaluated using the intra-class correlation coefficient model; internal consistency was tested with Cronbach’s alpha.

Results: The hypothesized moderate positive correlations for construct validity were supported; the strongest correlation was between the human activity profile adjusted activity score and the adult myopathy assessment endurance subscale score (r = 0.81; p < 0.0001). The PROs were able to discriminate between known high and low functioning groups for the adult myopathy assessment tool. Internal consistency of the PROs was high (α > 0.8) and there was strong reliability (ICC >0.62).

Conclusion: The PROs are valid and reliable measures of physical function in GNE myopathy and should be incorporated in investigations to better understand the impact of progressive muscle weakness on physical function in this rare disease population.

Implications for Rehabilitation

• GNE myopathy is a rare muscle disease that results in slow progressive muscle atrophy and weakness, ultimately leading to wheelchair use and dependence on a caregiver.

• There is limited knowledge on the impact of this disease on the health-related quality of life, specifically physical function, of this rare disease population.

• Three patient reported outcomes have been shown to be valid and reliable in GNE myopathy subjects and should be incorporated in future investigations to better understand how progressive muscle weakness impacts physical functions in this rare disease population.

• The patient reported outcome scores of GNE myopathy patients indicate a high risk for falls and impaired physical functioning, so it is important clinicians assess and provide interventions for these subjects to maintain their functional capacity.

Keywords:

• Psychometrics
• quality of life
• hereditary inclusion body myopathy
• reliability
• construct validity
• activities of daily living

Acknowledgements

We would like to thank John Perreault and Vandana Singhal for their roles in coordinating the natural history study and the nurses at the NIH Clinical Center for providing care to our participants during their visits. We would especially like to thank the participants of the natural history study for their participation and important role in improving our understanding of GNE myopathy.

Disclosure statement

The authors report no declarations of interest.

Additional information

Funding

This work was supported by the Intramural Research Programs of the National Human Genome Research Institute (no grant number associated), and the National Center for Advancing Translational Sciences (no grant number associated), National Institutes of Health, Bethesda, Maryland, United States.