Interhemispheric Pathways Are Important for Motor Outcome in Individuals with Chronic and Severe Upper Limb Impairment Post Stroke

BACKGROUND: Severity of arm impairment alone does not explain motor outcomes in people with severe impairment post stroke. OBJECTIVE: Define the contribution of brain biomarkers to upper limb motor outcomes in people with severe arm impairment post stroke. METHODS: Paretic arm impairment (Fugl-Meyer upper limb, FM-UL) and function (Wolf Motor Function Test rate, WMFT-rate) were measured in 15 individuals with severe (FM-UL ≤ 30/66) and 14 with mild–moderate (FM-UL > 40/66) impairment. Transcranial magnetic stimulation and diffusion weight imaging indexed structure and function of the corticospinal tract and corpus callosum. Separate models of the relationship between possible biomarkers and motor outcomes at a single chronic (≥6 months) time point post stroke were performed. RESULTS: Age (ΔR(2)0.365, p = 0.017) and ipsilesional-transcallosal inhibition (ΔR(2)0.182, p = 0.048) explained a 54.7% (p = 0.009) variance in paretic WMFT-rate. Prefrontal corpus callous fractional anisotropy (PF-CC FA) alone explained 49.3% (p = 0.007) variance in FM-UL outcome. The same models did not explain significant variance in mild–moderate stroke. In the severe group, k-means cluster analysis of PF-CC FA distinguished two subgroups, separated by a clinically meaningful and significant difference in motor impairment (p = 0.049) and function (p = 0.006) outcomes. CONCLUSION: Corpus callosum function and structure were identified as possible biomarkers of motor outcome in people with chronic and severe arm impairment.