Both projection and commissural pathways are disrupted in individuals with chronic stroke: investigating microstructural white matter correlates of motor recovery

Abstract

Background: Complete recovery of motor function after stroke is rare with deficits persisting into the chronic phase of recovery. Diffusion tensor imaging (DTI) can evaluate relationships between white matter microstructure and motor function after stroke. The objective of this investigation was to characterize microstructural fiber integrity of motor and sensory regions of the corpus callosum (CC) and descending motor outputs of the posterior limb of the internal capsule (PLIC) in individuals with chronic stroke and evaluate the relationships between white matter integrity and motor function.

Results: Standardized measures of upper extremity motor function were measured in thirteen individuals with chronic stroke. Manual dexterity was assessed in thirteen healthy age-matched control participants. DTI scans were completed for each participant. Fractional anisotropy (FA) of a cross-section of sensory and motor regions of the CC and the PLIC bilaterally were quantified. Multivariate analysis of variance evaluated differences between stroke and healthy groups. Correlational analyses were conducted for measures of motor function and FA. The stroke group exhibited reduced FA in the sensory (p = 0.001) region of the CC, contra- (p = 0.032) and ipsilesional (p = 0.001) PLIC, but not the motor region of the CC (p = 0.236). In the stroke group, significant correlations between contralesional PLIC FA and level of physical impairment (p = 0.005), grip strength (p = 0.006) and hand dexterity (p = 0.036) were observed.

Conclusions: Microstructural status of the sensory region of the CC is reduced in chronic stroke. Future work is needed to explore relationships between callosal sensorimotor fiber integrity and interhemispheric interactions post-stroke. In addition, contralesional primary motor output tract integrity is uniquely and closely associated with multiple dimensions of motor recovery in the chronic phase of stroke suggesting it may be an important biomarker of overall motor recovery.

Figure 1

White matter integrity in CC and PLIC in healthy individuals and patients with chronic stroke. In patients with chronic stroke, reduced mean FA values were observed in both the contra- and ipsilesional PLIC and in the primary sensory region of CC. Error bars represent one standard deviation from the mean. *p < 0.05.

Figure 2

Associations between contralateral PLIC integrity and multiple measures of motor function in patients with chronic stroke. In patients with chronic stroke, significant correlations were observed between contralesional PLIC mean FA and FM score, grip strength asymmetry and BBT asymmetry. *p < 0.05.

Figure 3

DTI-derived color and FA maps depicting region of interest drawings from a representative subject in the stroke group. A. Sagittal view of CC motor (yellow) and sensory (blue) regions as identified using Hofer and Frahm’s modified scheme [18]. B. Coronal view of right (pink) and left (orange) PLIC ROIs. C. Axial view of PLIC ROIs at level of the anterior commissure.