Abstract
BackgroundPerson-reported outcomes measurement development for rare diseases has lagged behind that of more common diseases. In studies of caregivers of patients with rare diseases, one relies on proxy report to characterize this disability. It is important to measure the child’s disability accurately and comprehensively because it affects caregiver burden. We aimed to create a condition-specific caregiver proxy-report measure for Duchenne Muscular Dystrophy (DMD) in order to understand the impact of DMD on the caregiver. Drawing on relevant item banks from the Patient-Reported Outcome Measurement Information System (PROMIS), we sought to confirm their reliability and validity in the target sample of DMD caregivers.MethodsThis web-based study recruited DMD caregivers via Rare Patient Voice, patient-advocacy groups, and word of mouth. Recruitment was stratified by age of the caregiver’s child with DMD, which broadly represents stages of DMD progression: 2–7, 8–12, 13–17, and > 18. Telephone interviews with DMD parent-caregivers pretested possible measures for content validity. The web-based study utilized an algorithm to categorize respondents’ ambulatory status for tailored administration of PROMIS Parent-Proxy items as well as some new items developed based on caregiver interviews. Item response theory analyses were implemented.ResultsThe study sample included 521 DMD caregivers representing equally the four age strata. The proxy-report measure included the following domains: fatigue impact, strength impact, cognitive function, upper extremity function, positive affect, negative affect, sleep-device symptoms, and mobility. The first five domains had strong psychometric characteristics (unidimensionality; acceptable model fit; strong standardized factor loadings; high marginal reliability). Negative Affect, covering anger, anxiety, depressive symptoms, and psychological stress, fit a bifactor model with good model fit, high marginal reliability, and strong factor loadings. The Sleep-device symptoms domain was not unidimensional, and the mobility domain did not have a simple structure due to residual correlations among items at opposite end of the mobility-disability continuum. These two domain scores were retained as clinimetric indices (i.e., uncalibrated scales), to achieve the overall goal of having a content-valid DMD-specific measure across all stages of disease severity.ConclusionsThe present study derived a DMD-specific proxy-report measure from PROMIS item banks and supplemental items that could potentially be utilized in caregiver research across all stages of the care recipient’s DMD. Future research will focus on assessing the responsiveness and validity of the measure over time and its comparison to DMD patient self-report.
Highlights
The introduction of person-reported outcomes (PROs) over the past few decades has facilitated clinical research in many ways
Scoring In order to increase the accessibility of the Duchenne Muscular Dystrophy (DMD) Impact Measure derived from Patient-Reported Outcome Measurement Information System (PROMIS) parent-proxy item banks, we provide two approaches for scoring the domains: (1) simple sums; (2) item response theory (IRT)-based T-scores
The present study created a DMD-specific proxy-report measure derived from PROMIS item banks that measure the full range of DMD outcomes noted as important and relevant by DMD caregivers
Summary
The introduction of person-reported outcomes (PROs) over the past few decades has facilitated clinical research in many ways. The early approach was to use a more generic measure, such as the SF-36TM [6, 7] for primary care [8], end-stage renal disease [9], arthritis [10], etc.; or, in some cases, to add some condition-specific items to fit the purpose (e.g., multiple sclerosis [11], epilepsy [12]) These early measures were later complemented by fully disease-specific PRO and proxy-report measures that tapped the relevant domains for the target condition (e.g., multiple sclerosis [13], arthritis [14, 15], epilepsy [16]). Drawing on relevant item banks from the Patient-Reported Outcome Measurement Information System (PROMIS), we sought to confirm their reliability and validity in the target sample of DMD caregivers
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