Optimal control of reaching is disturbed in complex regional pain syndrome: a single-case study

Abstract

Objective: Disturbance of goal-directed motor control may cause or exacerbate pathological pain in patients with complex regional pain syndrome (CRPS). We conducted a single-case study about motor control involved in reaching with a patient with CRPS in an upper limb.

Methods: Using a three-dimensional measurement system, we recorded reaching movement trajectories of the intact and affected hand before and after pain alleviation by therapeutic nerve blockade. We assessed degrees of tremor in the acceleration phase (from start until maximum peak velocity) and the deceleration phase (from maximum peak velocity until goal). To quantify the smoothness of reaching movements, we analyzed the curves of the trajectories during the initial movement phase (from start and maximum peak acceleration).

Results: The results showed that the tremor of the affected hand was greater than that of the intact hand during the deceleration phase, both before and after pain alleviation. Reaching trajectories of the intact hand smoothly traced curves convexed toward the intact side, while those of the affected hand represented unnaturally rectilinear functions associated with the loss of smooth movements. Further, these unnatural trajectories partially recovered after pain alleviation.

Conclusion: Disturbance of sensorimotor integration and pain-related fear might affect goal-directed motor control in CRPS patients.

Keywords: complex regional pain syndrome; motor control; reaching movement; sensorimotor integration.

Figure 1

Time series of goal-directed movement velocity in the intact upper limb (left) and in the affected limb before pain alleviation (middle) and after pain alleviation (right). Bradykinesia was observed in the affected limb (p < 0.017). However, slow reaching movements tended to improve after pain alleviation.

Figure 2

Examples of goal-directed movement trajectories in the intact upper limb (upper left) and in the affected limb before pain alleviation (lower left) and after pain alleviation (lower right). In the upper right bar graph, light-black, light-blue, and light-orange bars indicate tremor indexes during the acceleration phase in the intact limb and in the affected limb before and after pain alleviation, respectively. Respective dark-colored bars indicate the tremor indexes during the deceleration phase of these three conditions. The tremor indexes during the deceleration phase in the affected limb before and after alleviation were significantly higher than that in the intact limb (*p < 0.017).

Figure 3

Examples of goal-directed movement trajectories in the intact upper limb and in the affected limb before and after pain alleviation during the initial movement phase (upper column). The results of area under the curve (AUC) and trajectory direction during the initial movement phase are also shown (lower column). Upper column: The dotted line represents a straight trajectory between the start and goal positions in line with the sagittal body-midline axis. Positive values indicate rightward side (the affected side) and negative values indicate leftward side (the intact side). Lower column: Gray, blue, and orange bars indicate the results for the respective conditions. The AUC of each trajectory was measured by calculating the root mean square value. Trajectory directions in the three conditions are defined as angles between the body-midline axis and the initial movement direction of the intact and affected limbs. *p < 0.017; **p = 0.0001.