Multimodal Assessment of the Motor System in Patients With Chronic Ischemic Stroke

Abstract

Background and Purpose: Despite continuing efforts in the multimodal assessment of the motor system after stroke, conclusive findings on the complementarity of functional and structural metrics of the ipsilesional corticospinal tract integrity and the role of the contralesional hemisphere are still lacking. This research aimed to find the best combination of motor system metrics, allowing the classification of patients into 3 predefined groups of upper limb motor recovery. Methods: We enrolled 35 chronic ischemic stroke patients (mean 47 [26–66] years old, 29 [6–58] months poststroke) with a single supratentorial lesion and unilateral upper extremity weakness. Patients were divided into 3 groups, depending on upper limb motor recovery: good, moderate, and bad. Nonparametric statistical tests and regression analysis were used to investigate the relationships among microstructural (fractional anisotropy (FA) ratio of the corticospinal tracts at the internal capsule (IC) level (classic method) and along the length of the tracts (Fréchet distance), and of the corpus callosum) and functional (motor evoked potentials [MEPs] for 2 hand muscles) motor system metrics. Stratification rules were also tested using a decision tree classifier. Results: IC FA ratio in the IC and MEP absence were both equally discriminative of the bad motor outcome (96% accuracy). For the 3 recovery groups’ classification, the best parameter combination was IC FA ratio and the Fréchet distance between the contralesional and ipsilesional corticospinal tract FA profiles (91% accuracy). No other metrics had any additional value for patients’ classification. MEP presence differed for 2 investigated muscles. Conclusions: This study demonstrates that better separation between 3 motor recovery groups may be achieved when considering the similarity between corticospinal tract FA profiles along its length in addition to region of interest-based assessment and lesion load calculation. Additionally, IC FA ratio and MEP absence are equally important markers for poor recovery, while for MEP probing it may be important to investigate more than one hand muscle.

Structural or Functional Metrics to Assess Motor Impairment in Chronic Stroke?

“…Overall, Nazarova et al 11 showed that simple measures derived from diffusion MRI or TMS are insufficient for a correct outcome classification, in line with some previous reports. 3 Furthermore, their findings suggest that the combination of several CST FA measures including the Fréchet distance may provide a better proxy of upper limb motor function.…”

“…Although these results need to be replicated in larger samples, especially regarding the Fréchet distance, the relevance of microstructural metrics as potential biomarkers can be paralleled with other reports suggesting that diffusion MRI measures from a set of white matter tracts could predict walk recovery. 12,13 Finally, Nazarova et al 11 showed no benefit of a functional and structural multimodal approach. This may appear counter-intuitive according to the view the more, the better, as multimodal approaches are supposed to provide complementary information.…”

“…5 Yet, another study comparing several structural and functional approaches has reported that a TMS parameter (resting motor thresholds) was the only predictor of motor outcome. 10 How practice may change knowing the findings reported in Nazarova et al, 11 and what are the issues that remain to be addressed? Above all, the mechanisms of motor recovery need to be better investigated to reduce the fraction of variance unexplained by the current models and evaluate new therapeutics in postacute stroke.…”

“…6,7,10 Conversely, multimodal approaches based on the combination of structural and functional techniques may improve prediction accuracy. 3,5,8 An alternative perspective proposed by Nazarova et al 11 in a report in this issue of Stroke was to develop more sophisticated models at the metric level to evaluate whether combined measures derived from one single modality improve the prediction of upper limb motor performances in small samples. This study of 35 patients with unilateral hemispheric chronic stroke who underwent clinical motor tests as well as diffusion MRI and TMS assessment of the motor system tested if structural and functional multimodal metrics would provide complementary or redundant information on upper limb motor outcome.…”

Mapping of Motor Function with Neuronavigated Transcranial Magnetic Stimulation: A Review on Clinical Application in Brain Tumors and Methods for Ensuring Feasible Accuracy

“…Previously, it has been observed that the different somatotopically adjacent muscle representations could have different excitability profiles [ 95 , 107 , 118 ]. Albeit, at the group level the effect size may be minor or acceptable, at the individual level the clinical significance for such different profiles may be crucial [ 95 , 119 , 139 , 140 , 141 ]. This means that if a muscle has a lower rMT for activation and a steeper rise for the input–output curve than the other mapped muscles, the motor map will be biased due to the responses of that muscle, and will mostly present the representation area of that specific muscle over the other mapped muscles.…”