Research Article - (2022) Volume 4, Issue 3
Background: Sensory impairment severity may impact individual stroke survivors’ motor recovery as well as their response to peripheral sensory stimulation treatment.
Objective: To determine the effect of sensory impairment level of individual stroke survivors on motor improvement with therapy and peripheral sensory stimulation.
Methods: A secondary analysis of a pilot triple-blind randomized controlled trial. Twelve chronic stroke survivors participated in 2 weeks of hand task-practice therapy. They were randomly assigned to the treatment group receiving peripheral sensory stimulation or the control group receiving no stimulation during the therapy. Sensory impairment level was quantified as the pre-intervention sensory threshold. Motor improvement was assessed as change in the Box and Block Test score from pre to post-intervention. The association between sensory impairment level and motor improvement was examined using a regression analysis, accounting for groups.
Results: Participants with better sensation (i.e., with lower sensory threshold) had better motor improvement than patients with worse sensation (i.e., with higher sensory threshold). Sensory impairment level did not alter the effect of peripheral sensory stimulation.
Conclusion: The level of sensory impairment can be utilized to predict recovery potentials and direct rehabilitation treatment for stroke survivors.
Stroke rehabilitation • Upper extremity • Neurologic rehabilitation • Subliminal stimulation• Sensory function • Afferent pathways • Neural pathways • Wearable technology
Stroke affects more than 795,000 people per year in the U.S. and is a major cause of long-term disability [1] More than two thirds of stroke survivors have hand impairment [2] which limits their ability to perform activities of daily living [3,4]. In addition to motor impairment, sensory impairment is a common consequence of stroke. An estimated 50%-85% of chronic stroke survivors have sensory impairment, [5-7] with 37% of all stroke survivors experiencing long-term sensory deficits in the hand alone [8]. Sensory impairment significantly hinders motor learning9 and thus, may impede motor recovery [10-12]. However, sensory impairment level is not typically considered as a covariate for rehabilitation intervention outcome.
Peripheral sensory stimulation can be used to supplement manual therapy during rehabilitation since adding peripheral sensory stimulation enhances upper extremity motor recovery post-stroke [13,14]. Peripheral sensory stimulation activates not only the afferent pathway but also the motor cortex as seen by changes in neurophysiologic measures, thus priming the motor cortex for motor activities [15-17]. However, sensory impairment may curtail the effect of peripheral sensory stimulation due to disruption in the sensory processing pathways [18,19]. Yet, the impact of patients’ sensory impairment on the extent of hand functional recovery from therapy with peripheral sensory stimulation has not been examined. The objective of this study was to determine the effect of sensory impairment level of individual stroke survivors on motor improvement with therapy and peripheral sensory stimulation.
Study design
This secondary exploratory study is based on a triple-blind randomized controlled trial. Twelve chronic stroke survivors were randomly assigned to either the treatment group or control group (n=6/group). Both groups received hand task-practice therapy while wearing a peripheral sensory stimulation device on the paretic wrist for 2 hours/session, 3 times a week for 2 weeks. The device delivered imperceptible random-frequency vibration at 60% of the participant’s sensory threshold for the treatment group and no vibration for the control group. This vibration stimulates skin mechanoreceptors and elevates cortical neuronal firing for hand tasks [20,21] to improve sensorimotor function [22-26] and recovery in stroke survivors. Further description of this particular peripheral sensory stimulation and task-practice therapy used in this study can be found.
Participants
Participants were adult (age ≥ 18 years) chronic stroke survivors (≥ 6 months post-stroke) with mild-to-moderate upper limb impairment (Fugl-Meyer Upper Extremity Assessment (FMA-UE) scores 30-60/66 points) with cognitive ability to participate in task-practice therapy. None of the participants had botulin toxin injection in the paretic upper limb within 3 months of enrollment or concurrent upper limb therapy other than the study intervention. Participants had the mean age of 62 (SD=8) years, mean time post-stroke of 5 (SD=5) years, and mean FMA-UE score of 48 (SD=8). Demographic characteristics, including age, time post-stroke, and FMA-UE scores, were not significantly different between groups. All participants provided written informed consent. The study protocol was approved by the Medical University of South Carolina’s Institutional Review Board.
Assessments
The level of sensory impairment was quantified as the sensory threshold in this study. The sensory threshold was measured before the intervention as the lowest vibration amplitude at which the participant could feel the vibration at the wrist, determined using the staircase method [28]. The sensory threshold was expressed as percent of the maximum possible vibration amplitude (root mean square velocity of 68 mm/sec). Motor improvement following therapy was quantified as change in Box and Block Test scores from pre to post-intervention. The post-intervention Box and Block Test was completed on average 6 (SD=3.6) days after the last intervention day [14].
Analysis
A regression analysis was used to determine the relationship between sensory impairment level and motor improvement. The regression analysis included the between-participant groups (treatment and control) and the interaction between sensory impairment level and group. All statistical analyses were performed using SAS (SAS Institute Inc., Cary, NC, USA).
Sensory impairment level significantly predicted motor improvement (p=0.006) (Figure 1). Specifically, participants with better sensation (i.e., with lower sensory threshold) had greater motor improvement than participants with worse sensation (i.e., with higher sensory threshold). The treatment group had a greater motor improvement than the control group (p=0.0117). The interaction between group and sensory impairment level was not significant (p=0.949), indicating that the motor improvement decreased similarly in the two groups as the sensory impairment increased.
Figure 1. Association between sensory impairment level and motor improvement. Sensory impairment level was quantified as the pre-intervention sensory threshold. The motor improvement was quantified as change in the Box and Block Test score from pre- to post-intervention.
Sensory impairment is rarely considered in post-stroke motor rehabilitation [10,18] However, sensation is essential to enable feedback motor control [29,30] Longer feedback loops and direct projections from the cortical hand sensory areas to motor areas exist as evidenced by the cutaneomuscular reflex in humans [31,32] and intracortical micro stimulation studies in animals [33-36] These projections enable sensory feedback to affect motor output [37]. Thus, it follows that impaired sensation results in impaired motor function [38-41]. Many cross-sectional studies exist to show that stroke survivors with sensory deficits tend to have poor motor function [11,12,42-48] More importantly, sensory deficits hamper motor learning. Motor learning relies on development of an internal model to output motor commands that are appropriate for the motor state informed by the sensory feedback [49-51]. Sensory deficits, and thus impaired sensory feedback, likely interfere with development of an accurate internal model, thereby motor learning [52,53] The significant contribution of the present study is the presentation of longitudinal clinical data to suggest that greater severity of sensory impairment may diminish upper extremity motor recovery following intervention in chronic stroke survivors.
The present study provides insight into the importance of considering sensation for motor recovery. For example, sensory impairment level may be considered as a prognostic means to predict motor recovery. Improved prognosis may assist clinicians with determining appropriate rehabilitation goals, rehabilitation treatment, and discharge planning for individual stroke survivors. In addition, sensory intervention [54,55] may be a prerequisite to or in conjunction with motor intervention to promote motor recovery.
Interestingly, sensory impairment level did not alter the effect of the peripheral stimulation. All but one participant had some residual sensation, as seen by the sensory threshold less than 100% of the maximum possible amplitude. In addition, the peripheral stimulation was adjusted to be 60% of the sensory threshold for individual participants. Thus, it is possible that the residual sensory pathway, together with the individually adjusted peripheral stimulation amplitude, was able to yield the benefit of the peripheral sensory stimulation.
The primary limitation of this study is that it is exploratory and consequently has the small sample size. Larger studies are warranted, where additional covariates such as baseline motor function level, sex as a biological variable, age, and time since stroke could be examined. Other future research directions include investigation of the relative contributions of the sensory versus motor pathway integrity to post-stroke motor recovery as well as reorganization of these pathways with sensorimotor intervention.
This project was supported by NIH/NIGMS P20-GM109040, NIH/NICHD R01-HD094731-01A1, NIH/NCATS TL1-TR00145, NIH/NCATS UL1-TR001450, and DHHS/HRSA T08HP39300.
Dr. Na Jin Seo is the Principal Investigator of the study. Dr. Na Jin Seo and Jenna Blaschke conceived this study. Dr. Na Jin Seo, Jenna Blaschke, and Dr. Amanda Vatinno contributed to analysis. Drs. Amanda Vatinno and Viswanathan Ramakrishnan performed statistical analysis/interpretation. All authors contributed to result interpretation and writing of this manuscript. All authors reviewed and approved the final manuscript.
Dr. Na Jin Seo is an inventor of a patent regarding the investigated sub threshold vibratory stimulation. The other authors report no conflicts of interest.
Received: 29-Mar-2022, Manuscript No. NNR-22-58939; Editor assigned: 31-Mar-2022, Pre QC No. NNR-22-58939; Reviewed: 14-Apr-2022, QC No. NNR-22-58939; Revised: 30-May-2022, Manuscript No. NNR-22-58939; Published: 06-Jun-2022, DOI: 10.4172/ NNR.4.3.006
Copyright: © 2022 Blaschke J, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
