Abstract Body: Introduction: Repetitive peripheral sensory stimulation (RPSS) involves delivering electrical pulses to peripheral nerves to preferentially activate proprioceptive fibers and is a potential adjunct intervention for stroke motor rehabilitation. In the chronic phase after stroke, RPSS delivered above sensory threshold (suprathreshold) leads to improvements in hand strength compared to no stimulation. In the subacute phase, subthreshold RPSS (below sensory threshold) is more beneficial for hand dexterity than suprathreshold stimulation. Here, for the first time, we performed head-to-head comparisons of the effects of these two RPSS intensities on hand strength at different stages post-stroke.
Hypotheses: Subthreshold RPSS, compared to suprathreshold RPSS, will lead to greater gains in hand strength in the subacute phase after stroke. In the chronic phase, suprathreshold RPSS will be more beneficial.
Methods: In this multicenter, proof-of-principle, randomized clinical trial with blinded outcome assessment, 48 patients in the early subacute (8 to 90 days) or chronic (> 6 months) phases after stroke received either suprathreshold or subthreshold RPSS of the median nerve in the paretic arm for 2 hours. Grasp strength was measured before and after RPSS. Analysis was performed using Generalized Estimation Equations with factors "group" (subacute or chronic), "time" (before or after), and "intervention" (suprathreshold or subthreshold). Effect sizes were assessed using Cohen’s d.
Results: Significant interactions were found between “intervention” and “time” (Wald’s chi-square, 5.1; p = 0.024), and between “intervention” and “group” (Wald’s chi-square, 5.4; p = 0.020). Pairwise comparisons with Bonferroni corrections showed that hand strength significantly increased after suprathreshold (Confidence Interval, CI 95%, 1.15-28.5; Cohen’s d, 0.41) and subthreshold (CI 95%, 17.5-48.4; Cohen’s d, 0.81) RPSS. Other pairwise comparisons did not reach statistical significance.
Conclusions: Grasp strength improved after both suprathreshold and subthreshold stimulation in patients in the subacute or chronic stages after stroke. The effect size of subthreshold stimulation was large and two times greater than that of suprathreshold stimulation, suggesting that RPSS below sensory threshold should be preferred in future sham-controlled randomized clinical trials, either in the early subacute or chronic phases after stroke.