Quantitative assessment of finger motor impairment in multiple sclerosis

Abstract

Objective: To address the disability impact on fine hand motor functions in patients with Multiple Sclerosis (MS) by quantitatively measuring finger opposition movements, with the aim of providing a new "score" integrating current methods for disability assessment.

Methods: 40 MS patients (Expanded Disability Status Scale (EDSS): 0-7) and 80 healthy controls (HC) performed a repetitive finger-to-thumb opposition sequence with their dominant hand at spontaneous and maximal velocity, and uni- and bi-manually metronome-paced. A sensor-engineered glove was used to measure finger motor performance. Twenty-seven HC were tested twice, one month apart, to assess test-retest reliability.

Results: The motor parameters showed a good reproducibility in HC and demonstrated significantly worse performance in MS patients with respect to HC. A multivariate model revealed that rate of movement in the spontaneous velocity condition and inter-hand interval (IHI), indicating bimanual coordination, contributed independently to differentiate the two groups. A finger motor impairment score based on these two parameters was able to discriminate HC from MS patients with very low EDSS scores (p<0.001): a significant difference was already evident for patients with EDSS = 0. Further, in the MS group, some motor performance parameters correlated with the clinical scores. In particular, significant correlations were found between IHI and EDSS (r = 0.56; p<0.0001), MS Functional Composite (r = -0.40; p = 0.01), Paced Auditory Serial Addition (r = -0.38; p = 0.02). No motor performance parameter correlated with Timed 25-Foot Walk.

Conclusions: A simple, quantitative, objective method measuring finger motor performance could be used to define a score discriminating healthy controls and MS patients, even with very low disability. This sensitivity might be of crucial importance for monitoring the disease course and the treatment effects in early MS patients, when changes in the EDSS are small or absent.

Figure 1. Test-retest reliability of the motor performance parameters.

(A-E) Motor performance parameters in the two sessions performed one-month apart in a group of healthy controls (trial 2 vs. trial 1), with respect to the identity (i.e., the dashed line represents the bisector).

Figure 2. Comparison of the motor performance parameters between the two groups (HC and MS).

(A) RATE in the spontaneous and maximal velocity conditions, (B) Touch Duration in the 2 Hz condition, (C) Inter Tapping Interval in the 2 Hz condition, (D) Inter Hand Interval in the 2 Hz_bim condition. * indicates statistically significant difference between the two groups (HC and MS). Error bars indicate standard error of the mean.

Figure 3. ROC analysis.

The ability of the model of discriminating patients with MS from the HC group is demonstrated by the area under the ROC curve (AUC = 0.89 (95%CI = 0.820.96, p<0.001)), even when evaluated using a cross-validation procedure based on the leave-one-out method (AUC = 0.88 (95%CI = 0.81–0.95, p<0.001)).

Figure 4. Relationship between “Finger Motor Impairment score” and EDSS.

The weighted combination of motor performance parameters (“Finger Motor Impairment score”) given by the multivariate model was able to discern subjects from no disability to high level of disability (HC; patients with MS: EDSS = 0, EDSS = 1−2, EDSS = 2.5−4, EDSS>4) (p for trend <0.001). * indicates statistical significance with respect to healthy controls (HC group). Error bars indicate standard error of the mean.