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Detecting meaningful change using the North Star Ambulatory Assessment in Duchenne muscular dystrophy

Lookup NU author(s): Dr Anna Mayhew, Dr Michelle Eagle, Emerita Professor Katherine Bushby

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Abstract

AimClinician-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.MethodNSAA data were examined from 198 males (mean age at assessment was 8y 6mo [SD 2y 6mo] range 4y-18y; 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.ResultsOur 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.InterpretationThis 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.

Publication metadata

Author(s): Bushby K; Eagle M; Mayhew AG; Cano SJ; Scott E; Manzur A; Muntoni F; North Star Clinical Network

Publication type: Article

Publication status: Published

Journal: Developmental Medicine & Child Neurology

Year: 2013

Volume: 55

Issue: 11

Pages: 1046-1052

Print publication date: 01/11/2013

Online publication date: 05/08/2013

Acceptance date: 30/04/2013

ISSN (print): 0012-1622

ISSN (electronic): 1469-8749

Publisher: Wiley-Blackwell

URL: http://dx.doi.org/10.1111/dmcn.12220

DOI: 10.1111/dmcn.12220

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