Impaired object manipulation in mildly involved individuals with multiple sclerosis

Abstract

We investigated hand function in mildly involved multiple sclerosis (MS) patients (N = 16; Expanded Disability Status Scale 1-5, 9-hole peg test 14-32 s) during static and dynamic manipulation tasks using an instrumented device. When compared with healthy controls (N = 16), the patients revealed impaired task performance regarding their ability to exert prescribed patterns of load force (L; force acting tangentially at the digits-object surface). Regarding the coordination of grip force (G; normal component) and L, the data only revealed an elevated G/L ratio, although both the G and L coupling (maximum correlation coefficients and the time lags between them) and the G modulation (gain and offset of G with respect to L) remained comparable in the two groups. Finally, most of the data suggested no MS-specific effects of switching from uni- to bimanual tasks, from available visual feedback to deprived feedback conditions. We conclude that the deterioration in the ability for precise control of external forces and overgripping could precede the decoupling of G and L and decreased G modulation in early phases of the disease. The results also suggest that the applied methodology could be sensitive enough to detect mild levels of impairment of hand function in MS and, possibly, other neurological diseases.

Figure 1

(A) Schematic representation of the experimental device. The circles illustrate the position of the tips of all five digits applying precision grasp against two handles. On the left hand side the dimensions of the opposing grasping surfaces and the distance between them is depicted. The lower shaded rectangles illustrate the force sensors recording the instructed load force (L) exerted in vertical direction, while the upper ones recorded the grip force (G). (B) The stick diagram illustrates the horizontal projection of the body position and hand position, as well as the corresponding G.

Figure 2

(A) Right (RG) and left grip (LG), and right (RL) and left load force (LL) recorded in the lifting task in a representative MS patient and healthy control. The remaining graphs illustrate coefficients of variation (CV) (B), G/L ratios (C), and Z-transformed correlation coefficients (D) averaged across the subjects. Error bars represent standard deviations.

Figure 3

(A) Right (RG) and left grip (LG), and right (RL) and left load (LL) forces recorded in the ramp-and-hold task in a representative MS patient and a healthy control. (B) Grip-load diagrams represent the data depicted in Figure 3A together with the regression lines and the corresponding coefficients of determination (R²). The remaining graphs illustrate averaged across the subjects coefficients of variation (CV;) C), G/L ratios (D), Z-transformed correlation coefficients (E), and gain (F) and offset (G) that correspond to the slopes and intercepts of the regression lines. Error bars represent standard deviations.

Figure 4

(A) Right (RG) and left grip (LG), and right (RL) and left load (LL) forces recorded in the static oscillation task in a representative MS patient and healthy control. (B) Grip-load diagrams represent the data depicted in Figure 3A together with the regression lines and the corresponding coefficients of determination (R²). The remaining graphs illustrate the averaged across the subjects’ coefficients of variation (CV (C), I/I ratios (D), Z-transformed correlation coefficients (E), and gain (F) and offset (G) that correspond to the slopes and intercepts of the regression lines. Error bars represent standard deviations.