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DIFFUSION MR CORRELATES OF MOTOR FUNCTION RECOVERY AFTER STROKE: A SYSTEMATIC REVIEW
  1. Dheeraj Kalladka,
  2. Keith Muir
  1. University of Glasgow, Southern General Hospital, Glasgow

    Abstract

    Background Corticospinal tract (CST) integrity predicts the capacity for motor recovery after stroke and can be studied by diffusion–weighted MRI (DWI) sequences which measure random motion of water molecules along multiple directional gradients. By applying a diffusion tensor mathematical model at every brain voxel, several metrics can be derived that provide information on white matter tract microstructural integrity, including Fractional Anisotropy (FA), Apparent Diffusion Coefficient (ADC), Mean diffusivity (MD) and tractography. Neuroimaging parameters of CST integrity on its own, or along with functional MRI (fMRI) to investigate grey matter reorganisation, are proposed to aid patient selection for clinical trials (or in future, individualise rehabilitative or regenerative therapy selection), and serve as biomarkers of clinical change.

    Methods We performed a systematic review of Ovid Medline and EMBASE databases for published articles in English between inception & April 2011 that reported on Diffusion Tensor Imaging, fMRI, PET and MR Spectroscopy correlates of functional recovery.

    Results Of 9152 articles retrieved, 142 met criteria. Twenty one articles that reported on DTI parameters were included of which 20 were motor recovery studies and 1 visual. Ninety–one evaluated fMRI parameters (52 motor, 20 Aphasia, 3 Neglect, 5 Visual, 2 Cerebellar, 4 Gait & 3 Sensory/proprioception). Twenty–one evaluated PET parameters (13 motor, 5 aphasia, 2 neglect & 1 post stem cell implantation) & 3 evaluated MRS parameters. Among 20 DTI motor studies, 362 patients (mean age 55 yrs) were studied, of whom 70% were sub–cortical–only strokes, and 80% infarcts. Mean time from stroke onset to first DTI scan was 196 days with a range from 1 to 5100 days. Longitudinal DTI study designs comprising 91 patients were reported in 6 (30%) studies only including 2 case reports. Healthy volunteers as controls (mean age 46 yrs) were included in 9 (43%) studies. Ten studies reported near complete limb recovery with recovery times ranging from 3 to 30 months. Twelve studies measured FA of which 8 calculated correlations between FA and motor clinical scores but choice of region–of–interest (ROI) for FA extraction, clinical scores and statistical tests were heterogeneous. Eleven studies analysed tractography to either visualise or sub–group patients and investigate clinical scores. Six studies defined ROIs on tracts and derived FA and ADC. FA is reported as a better functional discriminator than ADC. Two studies reported functional reorganization and outcome was influenced by cortico–fugal fibres in addition to cortico–spinal tract integrity.

    Conclusions FA is the most commonly measured metric but there was considerable heterogeneity in study design and analysis. Most studies were cross–sectional, confined to sub–cortical, ischaemic strokes at late stages, and involved younger patients than typical of the stroke population. Further evaluation of the utility of DTI as a biomarker for use in stroke recovery trials is needed.

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