Calculation of the Minimal Clinically Important Difference in Upper and Lower Limb Motor Assessment in Spinal Muscular Atrophy

Abstract

Objectives: Physical function assessments in patients with spinal muscular atrophy (SMA) are important indicators for assessing the effectiveness of treatment and changes over time in rehabilitation therapy. However, few reports exist on this indicator. This study calculated the minimal clinically important difference (MCID) for assessing motor function in the upper and lower limbs of individuals with SMA to estimate the degree of change within a functional score that is considered clinically meaningful.

Methods: This cohort study relied on individual participant measurements. A distribution-based approach was used to calculate the MCID values, incorporating data from 26 patients with SMA for the 6-Minute Walk Test (6MWT), Hammersmith Functional Motor Scale Expanded (HFMSE), Revised Upper Limb Module (RULM), and grip and pinch strength.

Results: The standard errors of measurement for all patients were: 58.38 m for 6MWT; 4.71 points for HFMSE; 3.25 points for RULM; 10.93 N and 9.86 N for right and left grip strength, respectively; 5.42 N and 4.73 N for right and left Palmar pinch; and 11.96 N and 8.66 N for right and left Key pinch. Significant correlations were observed between the physical function assessments.

Conclusions: We calculated MCID values for physical function evaluations of SMA and, as a sub-analysis, determined the SMA type and ambulatory status. These findings are expected to contribute to future SMA treatment and rehabilitation and promote the selection of appropriate physical function assessments.

Keywords: 6-minute walk test; minimal clinically important difference; physical function assessment; spinal muscular atrophy.

Fig. 1.

Box-plot diagrams showing the variability in each physical function evaluation. a) HFMSE, b) 6MWT, c) RULM, d) grip strength, e) Palmar pinch, and f) Key pinch. RT, right; Lt, left.

Fig. 2.

Illustration of MCIDs in a) HFMSE, b) 6MWT, and c) RULM. Three distribution-based approaches for MCID were calculated for each subgroup: SEm (triangle), 1/2 SD (diamond), and 1/3 SD (circle).

Fig. 3.

Illustration of MCIDs in a) right grip, b) left grip, c) right Palmar pinch, d) left Palmar pinch, e) right Key pinch, and f) left Key pinch. Three distribution-based approaches for MCID were calculated for each subgroup: SEm (triangle), 1/2 SD (diamond), and 1/3 SD (circle). Plots marked with asterisk indicate results for data normalized according to body weight. Rt, right; Lt, left.