White matter integrity is a stronger predictor of motor function than BOLD response in patients with stroke

Recovery prediction like this is useless since there are no protocols given that will create white matter integrity.  All you are doing is predicting failure to recover and there is not a single stroke survivor in the world that wants to hear that.

White matter integrity is a stronger predictor of motor function than BOLD response in patients with stroke

 

Show all authors

Mingguo Qiu, MD, Warren G. Darling, PhD, Robert J. Morecraft, PhD, ...

First Published February 25, 2011 Research Article Find in PubMed 

https://doi.org/10.1177/1545968310389183

Article information

Abstract

Objective. 

 Neuroimaging techniques, such as diffusion tensor imaging (DTI) and blood oxygenation level–dependent (BOLD) functional magnetic resonance imaging (fMRI), provide insights into the functional reorganization of the cortical motor system after stroke. This study explores the relationship between upper extremity motor function, white matter integrity, and BOLD response of cortical motor areas.  

Methods. 

Seventeen patients met study inclusion criteria; of these 12 completed DTI assessment of white matter integrity and 9 completed fMRI assessment of motor-related activation. Primary clinical outcome measures were the Wolf Motor Function Test (WMFT) and the upper limb portion of the Fugl-Meyer (FM) motor assessment. Structural integrity of the posterior limb of the internal capsule was assessed by examining the fractional anisotropy (FA) asymmetry in the PLIC. Laterality index of motor cortical areas was measured as the BOLD response in each patient during a finger pinch task. Linear regression analyses were performed to determine whether clinical outcome was associated with structural or functional MRI measures. 

Results. 

There were strong relationships between clinical outcome measures and FA asymmetry (eg, FM score [R² = .655, P = .001] and WMFT asymmetry score [R² = .651, P < .002]) but relationships with fMRI measures were weaker.  

Conclusion. 

Clinical motor function is more closely related to the white matter integrity of the internal capsule than to BOLD response of motor areas in patients 3 to 9 months after stroke. Thus, use of DTI to assess white matter integrity in the internal capsule may provide more useful information than fMRI to interpret motor deficits following supratentorial brain injury.

Keywords

magnetic resonance imaging, diffusion tensor imaging, fractional anisotropy, laterality index, motor functional outcome

Introduction

Central mechanisms underlying upper limb motor recovery following stroke remain poorly understood. Clinical observations suggest that the initial levels of motor deficit and the course of recovery depend on corticofugal projection fiber integrity.^1-5 Diffusion tensor imaging (DTI) can appraise the integrity of white matter tracts by recording the fractional anisotropy (FA), which is derived from the eigenvalues of the diffusion tensor, to localize changes in white matter integrity due to local tissue damage or Wallerian degeneration after stroke.⁶ Furthermore, comparing the FA value of a well-defined pathway on one side of the neuraxis with the homologous pathway on the opposite side for signs of asymmetry provides insight toward the integrity and general health of a potentially injured or structurally declining white matter pathway. For instance, studies examining stroke patients with small homogeneous subcortical infarcts have found that larger asymmetries in FA are associated with poor motor recovery of the limb subserved by the injured pathway.⁷ Indeed, recent observations suggest that the potential for motor function recovery declines with increasing corticospinal tract disruption in stroke patients,^8,9 with no clinically meaningful gains appearing if DTI-derived FA asymmetry values exceed 0.25.¹⁰

Functional magnetic resonance imaging (fMRI) has provided important insights into the reorganization of the motor cortices after stroke.^11-13 The reported fMRI-derived patterns of motor system activation following stroke are variable and their interpretation regarding the recovery process is controversial.^14-17 Some studies suggest that positive motor recovery correlates with activation of the ipsilesional lateral premotor and supplementary motor areas when performing movements of the affected limb following stroke, particularly when the primary motor cortex (M1) is involved in the damage.^14,15 However, other reports suggest that bilateral patterns of cortical activity are associated with more favorable levels of motor recovery than ipsilesional activation alone, implicating a role for the contralesional motor areas in the recovery process.^17,18 Patients with good upper limb recovery after stroke have a significantly lower laterality index (LI) during finger tapping¹⁹ (ie, higher contralesional activity) than able-bodied volunteers, indicating relatively greater activation and potential contribution of the unaffected primary sensorimotor cortex (SM1). Conversely, poorly recovered chronic stroke patients exhibit low LI values.²⁰ However, these differences in LI values may subtend proportional differences in recovery stage since those in the Cramer et al¹⁹ study were 11 days to 15 months poststroke (combined acute and chronic phases or recovery), whereas Carey et al²⁰ enrolled patients who were 10 months to 21 years poststroke (all in chronic phase of recovery).

Although these studies have provided insight into recovery mechanisms after stroke, the specific neural substrates mediating recovery of hand motor function are not completely understood. Recent data suggest that pyramidal tract integrity is a strong predictor for focusing activation within affected primary sensorimotor cortex.²¹ The question remains as to the relative importance of the contribution of the cortical motor areas and their corticofugal projection systems to upper limb recovery following stroke. Furthermore, the relationship between motor system activation and white matter integrity remains poorly understood.¹³ The aim of the present study was to test the hypothesis that FA asymmetry in the posterior limb of the internal capsule (PLIC) and LI of the cortical motor areas are associated with upper limb motor functional outcomes in hemiparetic patients following stroke. Indeed, it is well known that the corticofugal projection from the frontal motor cortices to cervical spinal cord levels reside within the PLIC^1,22 and PLIC damage in humans results in upper extremity functional deficits.^1,4,5 We hypothesized that the degree of affected upper limb motor function will be correlated with FA asymmetry of PLIC and laterality of activated voxels in primary motor cortex in hemiplegic patients with moderate motor impairment 3 to 9 months poststroke. Specifically, superior motor function with the hemiplegic hand will be associated with lower FA asymmetry (ie, better integrity of PLIC) and higher LI (ie, higher ipsilesional activity).