Thomas Tourdias et al. inStroke
Early Fiber Number Ratio Is a Surrogate of Corticospinal Tract Integrity and Predicts Motor Recovery After Stroke.
Bigourdan A, Munsch F, Coupé P, Guttmann CR, Sagnier S, Renou P, Debruxelles S, Poli M, Dousset V, Sibon I, Tourdias T. Early Fiber Number Ratio Is a Surrogate of Corticospinal Tract Integrity and Predicts Motor Recovery After Stroke. Stroke. 2016 Apr;47(4):1053-9. 2016
Thomas Tourdias est membre du Team ‘Glia-neuron interactions’ Group leader: Stéphane Oliet, PhD du Neurocentre Magendie. Cursus de Thomas Tourdias: MD: Radiology, Bordeaux (2008), PhD: Neurosciences, Bordeaux (2011), Post doc: Stanford University, CA, USA (2013)
Cerebral ischemic stroke is a major cause of motor impairment with significant impact on the ability of patients to be self-sufficient in activities of daily living. Providing accurate prognosis of long-term motor impairment within the first few days after an insult is highly desirable (i) to correctly inform patients and caregivers; (ii) to rapidly anticipate the type, duration, and goals of rehabilitation; and (iii) to improve patient selection for clinical trials, such as those focusing on brain repair and reorganization.
The initial stroke severity is one of the most important predictor of long-term motor disability; mild-to-moderate patients at baseline being associated with favorable long-term outcome. In particular a proportional recovery rule states that many patients will recover ≈70% of their initial motor deficit. Nevertheless this rule seems to fail in patients with initial severe deficit because some did not recover at all while others can show substantial recovery.
In this paper, we hypothesized that quantifying the structural integrity of the motor pathway (i.e. the corticospinal tract) at the acute phase could inform on the potential of motor recovery over that provided by the 70% rule for resolution of motor impairment.
To test this hypothesis we prospectively included 117 stroke patients assessed acutely (24 to 72 hours after the insult) and at 1 year with diffusion tensor imaging (DTI) and motor scores. DTI is a magnetic resonance imaging technic that measures microscopic, natural displacements of water molecules in each voxel of a 3D image of the brain.
The rational for DTI is that water displacement is not the same in all directions, a phenomenon called anisotropy. Especially diffusion is faster in the direction of white matter fibers than in the perpendicular direction. 3D vector representing fiber orientation can thus be obtained in each voxel. Subsequent voxels can then be connected on the basis of their respective fiber orientation to reconstruct streamlines representing “virtual” fibers. By using this technic we computed the total number of corticospinal tract fibers ipsilateral to the stroke normalized by the total number of fibers from the contralateral side and we called this metric fiber number ratio (FNr).
We showed that:
(i) Initial FNr (iFNr) measured at the acute stage provides an early surrogate of chronic corticospinal tract fiber degeneration measured by FNr at 1 year follow-up.
(ii) iFNr is not mandatory for patients with mild-to-moderate stroke because those patients show a proportional recovery of ≈70% of their initial impairment which means that bedside measure of initial severity already provides a strong indication of future motor recovery (Figure 1-A).
(iii) iFNr provides strong added value toward predicting long-term motor impairment for the population of severely affected patients who demonstrate highly variable motor recovery unpredictable by clinical severity alone (Figure 1-B). Among those severe patients, persistent integrity of motor fibers assessed with iFNr is strongly associated with motor recovery. In particular patients with residual integrity of ≈30% of fibers (iFNr>0.26) are likely to recover by 70% of more (Figure 1-C and D; sensitivity=100%; specificity=83.5%; negative predictive value=100%; positive predictive value=72.7%; area under the curve=0.93±0.05; p=0.006)
In conclusion, we identified a metric which we called iFNr that is measurable in clinical routine before patient discharge from the hospital and that significantly improves our ability to identify the patients who are likely to recover. This predictive tool is of particular added value for patients with initially severe paresis. We expect this might improve stroke patient management by aiding in determining goals, type, and duration of rehabilitation.
(A) Mild-to-moderately affected patients (potential of recovery<50) recover about 70% of their initial impairment. The dashed line indicates the 70% rule prediction. (B) Severely affected patients (potential of recovery>50) demonstrate high variance in motor recovery. (C) In this severely affected population, patients with persistent motor fibers (iFNr>0.26, black dot) can also recover about 70% of their initial impairment while those with low amount of residual fibers (iFNr<0.26, red dots) don’t recover substantially (sensitivity=100%; specificity=83.5%; negative predictive value=100%; positive predictive value=72.7%). (D) Typical examples of two initially severe patients; one who don’t recover as expected based on the absence of residual motor fiber (red) while the other show substantial recovery of +53 points after 1 year as it could be predicted from residual fibers measured acutely.
Thomas Tourdias, MD, PhD, Bordeaux University Hospital, Neuroradiology, E-mail firstname.lastname@example.org
*Antoine Bigourdan, MD, department of neuroimaging, Bordeaux University Hospital
|*Fanny Munsch, PhD, department of neuroimaging, Bordeaux University Hospital|
* equal contribution