Structural integrity of corticospinal motor fibers predicts motor impairment in chronic stroke

Abstract

Objective: Motor impairment after stroke has been related to infarct size, infarct location, and integrity of motor tracts. To determine the value of diffusion tensor imaging (DTI) as a predictor of motor outcome and its role as a structural surrogate marker of impairment in chronic stroke, we tested correlations between motor impairment and DTI-derived measures of motor tract integrity.Methods: Thirty-five chronic stroke patients with varying degrees of recovery underwent DTI and motor impairment assessments. Fibers originating from the precentral gyrus were traced and separated into pyramidal tract (PT) and alternate motor fibers (aMF). Asymmetry indices of fiber number and regional fractional anisotropy (FA) values comparing lesional with nonlesional hemispheres were correlated with motor impairment scores and compared to an age-matched control group.Results: Fiber number and regional FA value asymmetry significantly differed between the groups with lower values in the patients' lesional hemispheres. Both measures significantly predicted motor impairment with stronger predictions when all motor tracts were combined as compared to predictions using only the PT. The pattern of motor tract damage (PT only vs PT and aMF) led to a classification of mild, moderate, or severe impairment with significant between-group differences in motor impairment scores.Conclusions: Diffusion tensor imaging-derived measures are valid structural markers of motor impairment. The integrity of all descending motor tracts, not merely the pyramidal tract, appears to account for stroke recovery. A 3-tier, hierarchical classification of impairment categories based on the pattern of motor tract damage is proposed that might be helpful in predicting recovery potential. Neurology Motor impairment after stroke has been related to lesion site and size, 1,2 amount of previous lesion burden, and other factors like age or comorbidities. 3,4 It has also been shown that the integrity of motor fibers, with the pyramidal tract (PT) as the main descending fiber bundle, but also the cortico-rubro-spinal or cortico-reticulo-spinal systems, 5,6 plays an important role for the degree of motor impairment which can be measured with standardized, reliable, and valid clinical assessments. 7,8 However, mere lesion location may not sufficiently demonstrate the extent to which motor fibers remain intact and a considerable amount of variance remains unexplained.Diffusion tensor imaging (DTI) allows for the visualization and quantitative examination of fiber tracts and their integrity in vivo 9 so that the topographic relation of lesion location and corticospinal fibers can be evaluated [10][11][12][13][14] and fiber degeneration can be revealed.

PREP2: A biomarker‐based algorithm for predicting upper limb function after stroke

“…Further work could usefully explore other neuroimaging biomarkers that might provide important prognostic information for MEP− patients. These may involve measures of alternative descending motor pathways,25, 26, 27, 28 and of the wider ipsilesional and contralesional sensorimotor networks, including the corpus callosum 29, 30, 31, 32, 33. However, more sophisticated measures may also require expertise not readily available in most clinical settings.…”

Primary progressive aphasia patients evaluated using diffusion tensor imaging and voxel based volumetry-preliminary results

“…Probabilistic tractrography uses the anisotropy of water and tract direction to generate probabilistic maps of connectivity between brain regions and it may draw fibers into the gray matter 15 . The number of fibers in each tract must be understood as a quantitative measure of connectivity between anatomical locations, as determined by the chosen region of interest (ROI) 16 . The loss of fiber loss by axonal degeneration secondary to neuronal injury occur after three months 17 .…”

Differential Adaptation of Descending Motor Tracts in Musicians

“…Previous studies comparing musicians with nonmusicians yielded contradictory results with regard to FA values in corticospinal motor tracts, and none of the studies related diffusivity measures to motor performance measures (Schmithorst and Wilke 2002;Bengtsson et al 2005;Han et al 2009;Imfeld et al 2009). Studies examining neural effects of long-term instrumental music practice have been complemented by studies showing white matter plasticity in response to the acquisition of other nonmusical sensorimotor skills (Scholz et al 2009;Hanggi et al 2010;Landi et al 2011) as well as in response to recovery from neurological disorders (Schlaug et al 2009;Wrigley et al 2009;Lindenberg et al 2010;Granziera et al 2012;Keil et al 2012;Zipse et al 2012) or neural effects of immobilization (Langer et al 2012). …”

“…These aMF might comprise the cortico-rubro-spinal and the cortico-reticulo-spinal tracts (Canedo 1997). They have been found to play an important role and show adaptations in motor recovery after lesions to the PT (Lindenberg et al 2010;Rüber et al 2012). The aims of our study were to test the hypotheses that (1) diffusivity measures of PT and aMF would show characteristic differences between keyboard players, string players, and nonmusicians and that (2) diffusivity measures of PT and aMF would be related to functional motor performance.…”