Impaired callosal motor fiber integrity and upper extremity motor impairment are associated with stroke lesion location

Background. Damage to the callosal motor fibers (CMFs) may affect motor recovery in patients with stroke. However, whether the severity of CMF impairment varies with lesion locations remains unclear. Objective. To investigate (1) whether CMF impairment occurs after stroke and whether the impairment varies with lesion locations and (2) the associations of CMF impairment and upper extremity (UE) motor impairment. Methods. Twenty-nine patients with lesions involving the corticospinal tract (CST) were categorized into 2 groups: lesions involving the CMFs (CMF group, n = 15), and lesions not involving the CMFs (non-CMF group, n = 14). Thirteen healthy adults served as the control group. Tract integrity, assessed by the mean generalized fractional anisotropy (mGFA) using diffusion spectrum imaging, of the CMFs and the CST above the internal capsule (CST _ABOVE ) of the ipsilesional hemisphere were compared. Results. After accounting for the effect of lesion load on the CST, the CMF group exhibited a significantly lower mGFA of the CMFs than did the control and non- CMF groups (post hoc P =.005 and.001, respectively). No significant difference was observed between the non-CMF and control groups (post hoc P =.999). The CST and CMF impairment accounted for 56% of the variance of UE motor impairment in the CMF group (P =.007), whereas no significant association was observed in the non-CMF group (P =.570). Conclusions. CMF impairment after stroke depends on lesion locations and CMF integrity has an incremental contribution to the severity of UE motor impairment in the CMF group.