New DMD Quality of Life Questionnaire Accurately Assesses Adults and Children

Philip Powell, PhD, CPsychol, AFBPsS

Researchers have developed a new patient-reported outcomes measure (PROM) for Duchene muscular dystrophy (DMD)—the DMD-quality of life (DMD-QoL). This new measure shows demonstrable content and face validity, according to a recent study.

Researchers generated the DMD-QoL, a 14-item QoL PROM, for use in patients with DMD from 7 years of age by proxy report and from 10 years of age by self or proxy report. The final version of the DMD-QoL showed good psychometric properties.

“Studies assessing health-related QoL in people with DMD suggest it is impaired compared to the general population. However, the ability of existing measures to adequately capture QoL in DMD has been questioned, with it posited that there is no optimal measure available,” wrote first author Philip Powell, PhD, CPsychol, AFBPsS, psychologist and research fellow, School of Health and Related Research, University of Sheffield, and colleagues.

To address this issue, Powell and colleagues used patient and public involvement and engagement in 3 steps. First, they generated draft items from 18 semi-structured qualitative interviews with boys and men with DMD. Second, they conducted cognitive debriefing interviews with 10 patients, 8 clinicians, and 10 patients’ parents to reduce and refine the items. Lastly, they took psychometric data on the draft items using a cross-sectional online survey with 102 respondents, and, with stakeholder input from patients and patients’ parents, produced the final questionnaire.

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Part 3 survey respondent ages ranged from 7 to 44 years (mean, 15.77; standard deviation [SD], 7.87). The final 14-item DMD-QoL correlated with the Comprehensive Model of QOL in MD (CMQM) in a 3-domain hierarchical model, (χ2 [74] = 81.91, P = .247; CFI = 0.982; RMSEA = 0.032 [0.000, 0.067], P = .761). No problems were detected in Mokken scale analysis (MSA). 

The final DMD-QoL consisted of 14 items, broken into 3 sets: physical functioning, psychological impact, and social participation. Items in physical functioning are “I found it hard to use my hands,” “I found it hard to eat,” and “I found it hard to breathe.” Items in psychological impact are “I was in pain,” “I felt tired,” “I found it hard to talk to people,” “I felt good about myself,” “I felt unhappy,” “I felt embarrassed,” “I felt worried,” and “I felt angry.” Items in social participation are “I found it hard to get around,” “I could take part in the things I wanted to,” and “I could take part in things with my friends.”

Average total score was similar between adults (27.6; SD, 6.4) and children (27.9; SD, 4.0; “adults” ≥16 years of age), although differences were seen in subscales. Adults scored significantly lower on the physical subscale (mean, 6.6; SD, 2.2) than children (mean, 8.0; SD, 1.5; t(71.38) = 3.45; P <.001). Accordingly, differences between adult in children were seen in the items “I found it hard to get around,” “I found it hard to use my hands,” “I found it hard to eat,” and “I found it hard to breathe.”

Adults scored significantly higher on the psychological subscale (mean, 16.9; SD, 3.5) than children (mean, 15.2; SD, 4.0; t(97.8) = 2.22; P = .029). Scores did not significantly differ on the social subscale between adults (mean, 4.1; SD, 2.3) and children (mean, 4.7; SD, 2.0). Children were more likely to endorse “I feel tired” on the psychological subscale, as well as “I could take part in things with my friends” in the social subscale.

Reported QoL was lowest in assisted reports (mean, 26.7; SD, 7.7), followed by proxy (mean, 27.4; SD, 5.5), and self-report (mean, 30.0; SD, 7.0) on the DMD-QoL. No significant differences were seen between reporting methods.

Powell and colleagues compared the DMD-QoL with many other measures. EQ-5D utility score was significantly higher in children (mean, 0.309; SD, 0.401), compared to adults (mean, 0.120; SD, 0.270; t(42.55) = 2.04; P = .047). As with the DMD-QoL, lowest utilities were reported for the assisted report (mean, −0.019; SD, 0.091), but utilities were also lower in the self-report (mean, 0.175; SD, 0.286) than proxy (mean, 0.279; SD, 0.392) group. The differences between groups were significant at the 10% level (F(2,54) = 2.611; P = .083).

There was a non-significant trend in children scoring lower in the Pediatric Quality of Life Inventory General Core Scales (PedsQL GCS) total score (mean, 44.1; SD, 16.7) than adults (mean, 46.4; SD, 12.3). In this measure, non-significant trends were also seen in that self-reported scores were highest (mean, 50.3; SD, 9.5), followed by assisted (mean, 43.9; SD, 14.2), and proxy report (mean, 43.7; SD, 16.3). 

“The 14 item DMD-QoL was designed in collaboration with, and for use in, the Duchenne community, to have good content validity relative to existing QoL PROMs. Initial analyses suggest DMD-QoL performs well in people with DMD (and their caregivers),” Powell and colleagues wrote.

“The DMD-QoL requires further independent validation and also needs to be compared for its performance against alternative QoL instruments. In the immediate next stage of its development, the measure will be valued to generate a preference-based measure that can be used to generate quality adjusted life years (QALYs) to inform resource allocation decisions within health technology assessments,” they concluded.

REFERENCE

Powell PA, Carlton J, Rowen D, Chandler F, Guglieri M, Brazier JE. Development of a new quality of life measure for Duchenne muscular dystrophy using mixed methods: The DMD-QoL. Neurology. Published online March 30, 2021. doi: 10.1212/WNL.0000000000011896