Abstract DP400: Responder Analysis of the TRANSPORT2 ( <i>TRANScranial direct current stimulation for Post stroke Recovery - a phase II sTudy)</i> : A post-hoc analysis

Introduction: TRANScranial direct current stimulation for Post stroke Recovery - a phase II sTudy (TRANSPORT2) was a multi-center trial in which ischemic stroke patients (1-6 months) with moderate upper extremity motor impairments were randomized to constraint-induced movement therapy with high dose (4mA), low dose (2mA), or sham transcranial direct current stimulation. The primary analysis found no significant differences in motor impairment among the three groups at days 15, 45, and 105, as measured by the Fugl-Meyer Upper Extremity (FM-UE) assessment. Methods: We conducted a post-hoc responder analysis. “Always-responders” were defined as subjects with FM-UE increases ≥6 points from the second baseline visit at days 15, 45, and 105. “Never-responders” were defined as subjects with FM-UE increases ≤5 from the second baseline visit at day 15, 45, and 105. Descriptive statistics of baseline characteristics are presented. Comparisons between the always-responder and never-responder groups were done using Welch’s t-tests and chi-square tests. Analyses were performed with RStudio (Posit PBC, Boston, MA), with significance set at α = 0.05. Results: We identified 28 always-responders and 37 never-responders. (Figure 1). Always-responders were younger (54.5±12.8 vs 62.8±10.5, p=0.007), enrolled sooner after stroke (100.6±42.6 vs 125.4±41.0, p=0.02), and were less likely to be enrolled in the 2 mA treatment group (sham=18.9% vs 35,7%, 2 mA=51.4% vs 21.2%, 29.7 vs 42.9%, p=0.04) (Table 1). There were no differences in race, handedness, side of motor weakness, NIHSS, lesion volume, weighted corticospinal tract lesion load (wCST-LL), presumed motor evoked potential (MEP) positivity, stroke impact scale (hand subscale), or the proportion who continued rehabilitation until day 105. Baseline FM-UE scores were similar (39.5±9.2 vs 34.2±13.8, p=0.068) between both groups. However, always-responders performed better in the Wolf Motor function Test (WMFT) (8.3±17.6, 35.5±50.0, p=0.0035) at baseline compared with never-responders. Conclusion: The phenotype of always-responders in the TRANSPORT2 clinical trial was that of a younger, more acute, and possibly more plastic subject. Despite similar baseline FM-UE scores to never-responders, always-responders had better WMFT scores, suggestive of preserved functional capacity that may have improved rehabilitation gains. The results of this hypothesis-generating, post-hoc analysis should be interpreted with caution.