D1Dimension 1 METHOD Three studies were performed. Two studies included only physiotherapy-treated patients, with 13 patients (males mean age 11y 7mo, SD 1y 10mo, range 8-14y) in the 3-month study and 41 patients (males mean age 14y 1mo, SD 5y 5mo, range 6-32y) in the 1-year study. A third study compared 12 patients treated with steroids with 12 age-and motor-function-matched untreated patients (males mean age of treated patients 10y 2mo, SD 2y 2mo range 6-14) over a 12-month period.RESULTS Over 3 months, the MFM D1 subscore (standing and transfers) decreased significantly ()4.7%; p<0.01). Over 1 year, all MFM subscores decreased significantly: )4.9% for D1 (p<0.01); )7.7% for D2 (axial and proximal motor capacity; p<0.01); )4.3% for D3 (distal motor capacity; p=0.03); and )5.8% for the total score (p<0.01). A threshold value for loss of ambulation and a predictive value 1 year before loss were estimated (total score 70% and D1 subscore 40%). Compared with the controls, patients treated with steroids had more stable total scores ()0.59 vs )5.87; p=0.02) and D2 subscores (0.98 vs )8.50; p<0.01).
Trial design for SMA depends on meaningful rating scales to assess outcomes. In this study Rasch methodology was applied to 9 motor scales in spinal muscular atrophy (SMA).
Data from all 3 SMA types were provided by research groups for 9 commonly used scales. Rasch methodology assessed the ordering of response option thresholds, tests of fit, spread of item locations, residual correlations, and person separation index.
Each scale had good reliability. However, several issues impacting scale validity were identified, including the extent that items defined clinically meaningful constructs and how well each scale measured performance across the SMA spectrum.
The sensitivity and potential utility of each SMA scale as outcome measures for trials could be improved by establishing clear definitions of what is measured, reconsidering items that misfit and items whose response categories have reversed thresholds, and adding new items at the extremes of scale ranges.
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