Mechanisms of arm paresis in middle cerebral artery distribution stroke: pilot study.

The development of effective neurobiological adjuvants to rehabilitation of paresis caused by stroke will depend on understanding mechanisms of paresis. Our objective was to determine the extent to which upper-limb (UL) paresis after nonlacunar ischemic middle cerebral artery (MCA) distribution stroke is caused by infarction of posterior periventricular white matter (PVWM), where corticospinal fibers serving movement descend, and caused by infarction of the arm-hand region of precentral gyrus (ahPCG). We conducted a blinded, retrospective analysis of computed tomography and magnetic resonance imaging from a convenience sample of 64 prospectively evaluated subjects with UL paresis resulting from MCA distribution stroke. Of the subjects, 96.5% had PVWM involvement while 53% had minimal or no ahPCG involvement. Even in subjects with no UL function, 56% had very minimal infarction (<25%) of the ahPCG. Degree of paresis was statistically associated with presence or absence of detectable posterior PVWM damage but not with extent of ahPCG involvement. These preliminary findings suggest that posterior PVWM involvement may be a major, if not the principal, determinant of paresis in all hemispheric ischemic strokes and motivate further prospective studies of this problem.