Wallerian degeneration in the corticospinal tract evaluated by diffusion tensor imaging correlates with motor deficit 30 days after middle cerebral artery ischemic stroke

Abstract

Background and purpose: The quantification and clinical significance of WD in CSTs following supratentorial stroke are not well understood. We evaluated the anisotropy by using DTI and signal-intensity changes on conventional MR imaging in the CST to determine whether these findings are correlated with limb motor deficit in patients with MCA ischemic stroke.

Materials and methods: We studied 60 patients within 12 hours of stroke onset. At admission, day 3, and day 30 of evolution, patients underwent multimodal MR imaging, including DTI sequences. We assessed the severity of limb weakness by using the motor subindex scores (5a, 5b, 6a, 6b) of the m-NIHSS and established 3 groups: I (m-NIHSS scores of 0), II (m-NIHSS, 1-4), and III (m-NIHSS, 5-8). FA values and rFAs were measured on the affected and the unaffected CSTs in the pons.

Results: FA values for the CST were significantly lower on the affected side compared with the unaffected side only at day 30 (P < .001), and the rFA was significantly correlated with the motor deficit at day 30 (P < .001; r = -0.793). The sensitivity, specificity, and positive and negative predictive values for motor deficit by rFA < 0.925 were 95.2%, 94.9%, 90.9%, and 97.4%, respectively.

Conclusions: WD in the CST revealed by DTI correlates with motor deficit 30 days after MCA ischemic stroke. This study highlights the utility of imaging follow-up at 30 days and the potential of DTI as a surrogate marker in clinical trials.

Fig 1.

Evolution of mean FA values and rFAs between the affected and unaffected sides in the region of interest in the descending CST at the level of the rostral pons in the function of m-NIHSS categories at admission, day 3, and day 30. Boxplots show median values (horizontal line inside the box), quartiles (box boundaries), and the largest and smallest observed values (lines extending from the box) of FA and rFA. Anisotropy values are clearly lower in patients with motor deficits at 30 days; no differences were found between patients in the m-NIHSS-II and m-NHISS-III groups.

Fig 2.

A 67-year-old man with acute right-sided striatocapsular infarction (upper left corner) who presented with severe hemiparesis (m-NIHSS, 8). Marked hyperintensity in the right descending CST on DWI at day 30 correlates with a decreased FA value and reduced brightness in the affected side, regarded as WD. Arrows indicate the affected right motor pathways at the level of the rostral pons

Fig 3.

rFAs between the affected and unaffected CSTs are lower in patients with motor deficits at 30 days; however, fewer than half presented with abnormal signal intensities on conventional MR imaging. The line parallel to the x-axis represents the prespecified cutoff point that discriminates patients with motor deficits on the basis of rFA. The graph shows medians and quartiles.