Stroke Lesion Impact on Lower Limb Function

Abstract

The impact of stroke on motor functioning is analyzed at different levels. 'Impairment' denotes the loss of basic characteristics of voluntary movement. 'Activity limitation' denotes the loss of normal capacity for independent execution of daily activities. Recovery from impairment is accomplished by 'restitution' and recovery from activity limitation is accomplished by the combined effect of 'restitution' and 'compensation.' We aimed to unravel the long-term effects of variation in lesion topography on motor impairment of the hemiparetic lower limb (HLL), and gait capacity as a measure of related activity limitation. Gait was assessed by the 3 m walk test (3MWT) in 67 first-event chronic stroke patients, at their homes. Enduring impairment of the HLL was assessed by the Fugl-Meyer Lower Extremity (FMA-LE) test. The impact of variation in lesion topography on HLL impairment and on walking was analyzed separately for left and right hemispheric damage (LHD, RHD) by voxel-based lesion-symptom mapping (VLSM). In the LHD group, HLL impairment tended to be affected by damage to the posterior limb of the internal capsule (PLIC). Walking capacity tended to be affected by a larger array of structures: PLIC and corona radiata, external capsule and caudate nucleus. In the RHD group, both HLL impairment and walking capacity were sensitive to damage in a much larger number of brain voxels. HLL impairment was affected by damage to the corona radiata, superior longitudinal fasciculus and insula. Walking was affected by damage to the same areas, plus the internal and external capsules, putamen, thalamus and parts of the perisylvian cortex. In both groups, voxel clusters have been found where damage affected FMA-LE and also 3MWT, along with voxels where damage affected only one of the measures (mainly 3MWT). In stroke, enduring 'activity limitation' is affected by damage to a much larger array of brain structures and voxels within specific structures, compared to enduring 'impairment.' Differences between the effects of left and right hemisphere damage are likely to reflect variation in motor-network organization and post-stroke re-organization related to hemispheric dominance. Further studies with larger sample size are required for the validation of these results.

Keywords: activity limitation; brain mapping; compensation; impairment; lower extremity; restitution; stroke.

FIGURE 1

Lesion overlay maps of left hemisphere damage (LHD, n = 38) and right hemisphere damage (RHD, n = 29) patient groups. Representative normalized slices (out of 90 normalized slices employed) are displayed in radiological convention (right hemisphere on left side and vice versa), with warmer colors indicating greater lesion overlap (units: number of patients with lesion in this region).

FIGURE 2

VLSM analysis depicting areas where damage was associated with significantly lower scores of Fugl-Meyer assessment lower extremity (FMA-LE) and 3 m walk test (3MWT) following (A) left hemisphere damage (LHD) and (B) right hemisphere damage (RHD). Minimum cluster size: 10 voxels, minimum number of patients affected in a voxel (15% of n: 6 and 4, respectively). Warmer colors indicate higher z-scores. The colored regions in B (RHD) survived FDR correction for multiple comparisons, but the colored regions in A (LHD) did not, and represent a lenient criterion of significance – z-score ≥ 2.00 (p ≤ 0.02). IR, irrelevant, all structures in this case shared a single z-score.

FIGURE 3

Conjunction analysis depicting areas of brain damage that were associated with lower scores in the Fugl-Meyer assessment lower extremity (FMA-LE) only, 3 m walk test (3MWT) only and both FMA-LE and 3MWT, shown in blue, yellow and green, respectively, in the left hemisphere damage (LHD, n = 38) and right hemisphere damage (RHD, n = 29) groups.