Objective

The “quality of life in neuromuscular disease” questionnaire (QoL-NMD) is a new health-related quality of life measurement tool specifically designed for patients with a slowly-progressive neuromuscular disease with motor deficiency. The QoL-NMD is structured into 3 domains: “impact of physical symptoms”, “self-perception” and “activities and social participation”. Our objective is to estimate conditional minimum detectable changes (cMDCs). The cMDCs help determine if a measure change reflects a change of patient’s status over time or a measurement error.

Material/patients and methods

The QOL-NMD was administered to patients recruited in 8 tertiary hospitals dedicated to NMD. Each QoL-NMD domain was measured by a T score metric i. e. a normal distribution with a mean of 50 and a standard deviation of 10. High values represent good quality of life. Standard errors of measurement were estimated using items response theory. For each QoL-NMD domain we estimated the cMDCs associated with all measure changes.

Results

A total of 315 patients were recruited. Estimated cMDCs were generally smallest in the mid-range of all scales (between 9 and 12) and higher on the outer quartiles (up to nearly 17). The lowest mid-range cMDCs were for the domain “activities and social participation” (almost all below 10).

Discussion – conclusion

These results provide a clinically useful means of interpreting change for individual patients on the QoL-NMD. The cDMC tables can help clinicians and investigators identify differences for individual patients that are clinically relevant to reflect a status change and motivate a modification of care.