Development of a phone application for assessing fatigue levels in rare disorders: a feasibility and validity study

Abstract

Purpose Barth syndrome (BTHS) is a rare genetic disorder characterized by skeletal myopathy, cardiomyopathy, and exercise intolerance due to early fatigue. The purpose of this study was to test the feasibility and validity of a new phone application designed to capture multi-dimensional aspects of fatigue across the lifespan. The specific study aims were to (1) assess the feasibility of using the app to record perceived fatigue levels in real-time, (2) evaluate discriminant validity by assessing if the app can differentiate between those with and without BTHS, and (3) content validity by assessing the relationship between perceived energy levels and actual energy expenditure. Methods Eighteen participants with BTHS and 18 age-matched control participants completed the study. The participants wore an activity tracker for 14 days and were prompted to respond to an Android app to report their fatigue levels 6 × /day. Statistical analysis was completed to examine perceived fatigue and the relationship between reported fatigue and actual energy expenditure. Results Feasibility was supported by the majority of participants responding to at least 50% of the application prompts and scores indicative of good internal consistency between responses (92–95%) and reliability of the battery scale (p < .001). Discriminant validity of the app was only partially supported, with the number of “crashes” being significantly different between those with and without BTHS (p = 0.042). Other measures of perceived fatigue were not found to be significantly different between groups, even though individuals with BTHS showed significantly lower energy expenditure than control participants during the day as measured by actigraphy (p < 0.001). Content validity of the app was supported, with perceived energy levels significantly correlating with actual energy expenditure collected with the activity tracker (p < 0.001). Conclusions In summary, the phone app developed by our team allowed researchers to capture the lived experience of individuals with BTHS while also capturing objective data. We verified that the app was able to consistently and accurately capture participant-reported fatigue. The battery scale tested as part of our feasibility aim was successful in capturing perceived levels of energy and can be used as a valid measure of fatigue in future studies. It was interesting to note that “crashes” appear to be the main differentiating factor in fatigue between the BTHS and control participants, where other measures of perceived fatigue were not found to be significantly different. These results highlight the complex nature of measuring fatigue as a subjective construct. This study provides foundational information on methods for quantifying fatigue in adults, adolescents, and children with BTHS and can provide possible targets for future therapeutic trials.