Detecting meaningful change using the North Star Ambulatory Assessment in Duchenne muscular dystrophy
Anna G Mayhew, Stefan J Cano, Elaine Scott, Michelle Eagle, Kate Bushby, Adnan Manzur, Francesco Muntoni, North Star Clinical Network for Neuromuscular Disease, Allison Morgan, Fiona Bull, Eva Es, Marika Pane, Filippo Buccella, Francesca Ceradini, Fernanda De Angelis, Imelda de Groot, Birgit Steffensen, Meredith James, Kate Bushby, Michela Guglieri, Francesco Muntoni, Anna G Mayhew, Stefan J Cano, Elaine Scott, Michelle Eagle, Kate Bushby, Adnan Manzur, Francesco Muntoni, North Star Clinical Network for Neuromuscular Disease, Allison Morgan, Fiona Bull, Eva Es, Marika Pane, Filippo Buccella, Francesca Ceradini, Fernanda De Angelis, Imelda de Groot, Birgit Steffensen, Meredith James, Kate Bushby, Michela Guglieri, Francesco Muntoni
Abstract
Aim: Clinician-reported outcome instruments such as the North Star Ambulatory Assessment (NSAA) need to be able to detect clinically important change to be suitable for clinical trials. However, in Duchenne muscular dystrophy (DMD), identifying changes in function is not straightforward. In this study, we use Rasch-transformed data to examine the responsiveness and minimal important difference (MID) of the NSAA in males with DMD receiving different corticosteroid regimes.
Method: NSAA data were examined from 198 males (mean age at assessment was 8 y 6 mo [SD 2 y 6 mo] range 4 y-18 y; 805 assessments). Responsiveness was assessed using mean score changes (using Rasch-transformed data) between adjacent pairs of age groups, pairwise squared t-values from paired samples t-tests, and an effect size calculation. The MID was assessed using the effect size calculation and 0.5 standard deviation (SD) of mean score differences.
Results: Our findings revealed a difference in change scores over time between the two corticosteroid regimes. Mean NSAA person estimates were higher in the daily prednisolone group. The mean MID (0.5 SD) was 8.8 and 6.9 for the daily group and intermittent group respectively.
Interpretation: This study, based on Rasch-transformed NSAA data, provides an initial basis for the interpretation of clinical change in DMD over time and between corticosteroid regimes. Our proposed MIDs can be mapped back to differences in specific item content across the range of the NSAA.
© 2013 Mac Keith Press.
Source: PubMed