Disturbances of spatial reference frame and postural asymmetry after a chronic stroke

Asymmetrical postural behaviors are frequently observed after a stroke. They are due in part to the sensorimotor deficit, but they could also be related to a disorder of the representation of the body in space. The objective was to determine whether the asymmetrical postural behaviors of chronic stroke patients are related with a disruption of the perception of spatial frame. 30 chronic stroke patients (mean age 60.3 year ± 10, mean delay post-stroke 4.78 year ± 3), 15 patients with right brain damage (RBD) and 15 patients with left brain damage (LBD), and 20 healthy subjects participated in the study. Postural asymmetry was detected by the evaluation of body weight repartition on a force platform (weight body asymmetry) and was related to the longitudinal body axis (LBA) and the subjective straight ahead (SSA) (egocentric space representation) and to the subjective visual vertical (SVV) (allocentric space representation) by a multivariate analysis of variance adjusted with motor function and sensitivity as covariables. Both patients with RBD (35% ± 8) and LBD (39% ± 4) had body weight asymmetry and there was still space misperception at this stage of recovery, especially in the RBD group. WBA was related to LBA when considering both patients with RBD and LBD (p = 0.03). However, this relation was dependent on the side of the lesion (p = 0.0006) with a stronger relation in the RBD group (0.01). No relation with WBA was found neither with SSA (p = 0.58) nor with SVV (p = 0.47). This study pointed out a strong relationship between disturbance in the perception of the longitudinal body axis and postural asymmetry in chronic strokes, and especially within the RBD group. Conversely, no other spatial perturbations seemed to be involved in this particular postural behavior.