We obtained a representative sample in terms of diagnosis, with a predominance of deletions (66%), a 12% rate of duplications and a point mutation rate of 22% consistent with the literature . The total MFM score varied from 1 to 98.90% (median of 57%) ranging from patients with less severe up to very severe motor impairment. Corticosteroids were administered to 57.8% of the population compared with 85% for the English-language validation, probably due to divergences between English and French language guidelines.
Fidelity of the PedsQLTM3.0DMDfv: internal consistency
Our results showed good internal consistency for the parents’ scores, except for the Treatment dimension. For the children, internal consistency was acceptable only in the Daily Activities dimension, which provides objective information on everyday living. In the validation study of the original English-language version, with 200 parents and 117 children (i) the internal consistency was better, with Cronbach’s alpha close to 0.8 (ii) the difference between the children’s and parents’ data was less significant with parents’ data showing higher Cronbach’s alphas, (iii) the lowest Cronbach’s alpha for both datasets was in Treatment dimension .
In our French version, the lower internal consistency for both children and parents’ scores -compared to validation study of the original English-language version- could probably suggested a misunderstanding of the several items. For example, children found difficult to understand the concept of Treatment in our initial translation process. We therefore replaced it by Medicines and Physiotherapy. In clinical practice, this item could be even more specific with the names of the medications or the number of tablets taken per day, which would help the children to give a more precise answer. Another explanation could be that the heterogeneity of our sample, ranging from less severe up to severe impairments, could warrant this finding. We therefore conducted an assessment by severity, which allowed us to examine the scale’s internal consistency separately in several subgroups. It remained imprecise due to the low numbers, but conclusions did not change: the internal consistency was insufficient for the children’s questionnaires and satisfactory for the parents’ questionnaires, with a similar distribution of scores.
Analysis of internal consistency and its sensitivity revealed good internal consistency, especially for the responses from the parents’ group and the severe group of children. This analysis was not performed in the original validation.
In our study, the differences between the children’s and parents’ findings were greater than in the validation study of the original English version, with the parents’ data showing higher Cronbach’s alphas. The lowest Cronbach’s alpha for both datasets was for the Treatment dimension . The difference can be explained by a change in the wording of items in our French translation. Indeed, although identical for all ages in the children’s or the parents’ questionnaires, the items were formulated differently for the children and their parents. This difference was marked for item 4: “I am having trouble living with my illness [children]” and “Difficulties in managing his/her muscle disorder [parents]”. However, the back translation was correct. This item 4 seems to be related more to the Worry dimension than to the Treatment dimension. However, it is ranked in Treatment dimension (in the original version and consequently in our French translation) which can be a little confusing.
Internal consistency was lower for the Treatment dimension for the parents’ assessments and was better for the Daily Activities dimension (which provides objective and representative information on everyday living) for the children’s assessments. Our results were consistent with the original English version where the lowest Cronbach’s alpha for both datasets was in the Treatment dimension .
First, the convergent validity was satisfactory for each item in the Daily Activities and Communication subscales, for both child and parent ratings. It was also good for the Treatment and Worry subscales, but only for the parents’ assessments. The correlation coefficients were higher in the Daily Activities dimension than in the other dimensions. These findings seem logical. The Daily Activities dimension reflects motor impairment and severity and is composed of objective items. The Worry and Communication dimensions are more subjective and are much more directly dependent on the child or the parents’ feelings, which makes probably them less reliable.
Second, several items from various dimensions were positively correlated with items of a different dimension. For example, item 3 of the Treatment dimension appeared to be more closely associated with the Daily Activities dimension sub-scores, which is consistent with the fact that the Daily Activities dimension is the more objective dimension and the one more closely linked to motor impairments.
The same pattern was found for item 4 of the Treatment dimension, which appeared to be associated with the Daily Activities, Treatment, and Worry dimensions. It is possible that this item could be too subjective in its interpretation. This analysis was not reported in the original validation article.
Third, most of the correlations between the questionnaire dimensions were moderate. The Communication dimension showed little correlation with the other dimensions. This raises the question of its relevance and therefore that of the notion of an overall QoL score. In the original validation, these correlations were not performed.
Finally, for the oldest children with severe DMD, the QoL reported by the children and their parents was significantly poorer for the Daily Activities dimension. For the other dimensions, the results were not significant. Our result was consistent with the original article where, for the Daily Activities dimension, QoL was significantly better for the 8–12-year-old children than for the 13–18-year-olds, both for children and parents. This previous result was reinforced by a significant difference -both for children and parents- between children needing mobility aids and those moving without assistance: QoL was deemed to be better for those who didn’t use mobility aids or could walk . Similarly, Davis et al., in their 2010 study to validate the neuromuscular module for the DMD population, also found that children and parents reported a poorer QoL compared to a healthy population, most importantly in the physical dimension. QoL was significantly better in patients who did not use a wheelchair or very rarely compared to those who used one all the time . Thus, as with previous studies, ours clearly demonstrated the progressive chronic condition component of DMD, leading to irreversibly reduced physical condition, mobility and autonomy, and consequently a gradual decline in QoL.
Agreement between self- and proxy-assessments
The overall trend was that proxy-assessments scores (parents) were lower than self-assessments (children): parents rated their child’s QoL worse than their children thought. The difference was more marked for subjective items corresponding to feelings (Worry and Communication dimensions) compared to more objective items (Treatment and Daily Activities dimensions). For the Worry dimension, the correlation was better between proxy-assessment (parent) and self-assessment (child) scores when the child’s QoL was good. Our findings showed the same trend as the original study: the ICC was between 0.61–0.80 for Daily Activities, which indicated good agreement, and moderate For Treatment and Worry (ICC = 0.41–0.60). The weakest ICC was for the Communication dimension . This perception gap-both in original and in our translation- may be linked to the considerable difficulty parents had in understanding their position when replying to the questionnaire. Several parents thought that they had to assess their own QoL.
Our French version of the scale showed poor agreement between the parents and children, similar to the findings on the original English scale. The agreement was better for objective functions (activities of daily living) and lower for more subjective functions (Worry, emotions). Children appeared less worried than their parents in both versions. This result is consistent with literature on this subject and refers to the “disability paradox” or “well-being paradox” [25, 26], a process of adapting to changes in health and accommodation to illness. Children think they have a better QoL than their parents, because they have become accustomed to their diseases. This is the only life they know and they rate their QoL as relatively good, and perceive their well-being differently. Reference can also be made to the “coping strategy”, an adaptation strategy that helps protect against the adverse effects of disease. Explaining the “disability paradox” to families might therefore give them a more positive view of their child’s experience.
Another explanation to explain this difference is that parents have different perspectives on their child’s illness, and they probably feel more anxious about the future. They adjust their perceptions based on their knowledge of the natural course of the disease and think negatively about the future . Also, parents are often overwhelmed by the care and their negative perceptions can also be explained by the “burden” of being an informal caregiver . DMD leads to intense and prolonged family involvement, leading to physical, psychological and financial consequences . It will be probably necessary in the future to assess the parents’ QoL -or at least to collect data on their mental health or their own difficulties- in order to interpret the results more precisely.