Corticospinal tract lesion load: An imaging biomarker for stroke motor outcomes.

Objective: The aim of this work was to investigate whether an imaging measure of corticospinal tract (CST) injury in the acute phase can predict motor outcome at 3 months in comparison to clinical assessment of initial motor impairment.

Methods: A two-site prospective cohort study followed up a group of first-ever ischemic stroke patients using the Upper-Extremity Fugl-Meyer (UE-FM) Scale to measure motor impairment in the acute phase and at 3 months. A weighted CST lesion load (wCST-LL) was calculated by overlaying the patient's lesion map on magnetic resonance imaging with a probabilistic CST constructed from healthy control subjects. Regression models were fit to assess the predictive value of wCST-LL and compared with initial motor impairment.

Results: Seventy-six patients (37 from cohort 1 and 39 from cohort 2) completed the study. wCST-LL as well as assessment of motor impairment (UE-FM) in the acute phase correlated with motor impairment (UE-FM) at 3 months in both cohort 1 (R(2)  = 0.69 vs. R(2)  = 0.67; p = 0.43) and cohort 2 (R(2)  = 0.69 vs. R(2)  = 0.62; p = 0.25). In the severely impaired subgroup (defined as UE-FM ≤ 10 at baseline), wCST-LL correlated with outcomes significantly better than clinical assessment (R(2)  = 0.47 vs. R(2)  = 0.11; p = 0.03). In the nonseverely impaired subgroup, stroke patients recovered approximately 70% of their maximal recovery potential. All stroke patients in both cohorts had poor motor outcomes at 3 months (defined as UE-FM ≤ 25) when wCST-LL was ≥ 7.0 cc (positive predictive value was 100%).

Interpretation: wCST-LL, an imaging biomarker determined in the acute phase, can predict poststroke motor outcomes at 3 months, especially in patients with severe impairment at baseline.