Neuromuscular electrical stimulation on upper limb function post-stroke

Abstract

Invited Commentary on: ‘Advances in neuromuscular electrical stimulation for the upper limb post stroke’, Hayward et al. Hayward et al.’s review paper summarizes the current applications of neuromuscular electrical stimulation (NMES) and the treatment effects of different types of NMES in the impairment, activity, and participation domains of International Classification of Functioning, Disability and Health model for stroke patients. In addition, they suggested future research directions for NMES research. We would like to remind readers that there is another important question for future research, i.e. the influence of NMES parameters (stimulation time, intensity, treatment duration, and target muscles) on affected upper limb recovery post-stroke. It has been suggested that parameters of electrical stimulation are likely to be crucial factors related to treatment effect. Owing to the heterogeneity of NMES parameters adopted in the articles reviewed in the current study, the readers must be cautious while applying the results from this study to their individual patients. According to motor learning theories, repetition is important for improving movement performance. Hence, it is reasonable to assume that there might be a positive relationship between number of practice trials and motor performance improvement. Previous studies have demonstrated that increasing exercise time led to better functional outcomes. Can we apply this principle for NMES treatment? Will higher doses of NMES lead to better arm function recovery than lower doses of NMES? What is the optimal treatment dose for selected NMES to improve impairment or function of the upper limb after stroke? The answers to these questions remain ambiguous because the stimulation doses of NMES ranged widely from as little as a total of 6 hours to more than 200 hours among studies. The minimal effective dose for improving upper limb function from our own study was 10 hours. Our study revealed that dosage of NMES was a significant predictor for upper limb function improvement and increasing the stimulation dose of NMES led to greater improvement in the action research arm test score at follow-up. Another important issue in NMES application is the influence of selection of target muscles. de Kroon et al.’s study showed that there was no significant difference between alternating stimulation of the hand extensor and flexor muscles or stimulation hand extensors only. Our study found that patients who received stimulation of both hand flexor and extensor muscles showed greater improvement as compared with those receiving stimulation of extensor muscles. Furthermore, de Kroon et al.’s review paper reported an increased likelihood of a positive outcome if elbow and shoulder muscles were stimulated in addition to wrist and/or finger extensors. The relationship between stimulated target muscles and arm function remains unclear based on current available evidences. Hayward et al. suggested that more studies are needed to investigate effects of NMES on patients with severe paresis or paralysis in acute stage. This could provide more information for clinicians regarding which stroke patients will benefit from NMES intervention or is suitable for which types of NMES. Some studies supported the treatment effect of NMES in the acute phase; however, few studies have applied NMES in patients with severe paresis. Our own experience indicated that cyclic NMES can be applied to patients in the acute flaccid stage or to patients with severe arm weakness with satisfactory results on both the impairment and the function levels. NMES is a useful adjunct therapy for stroke rehabilitation during both acute and chronic stages. The current review paper provided an overview of current and emerging NMES applications. It offers a good overview for clinicians to select appropriate NMES techniques for improving either the impairment or function of upper limb after stroke. For future studies, we hope that more information on the influence of NMES parameters on affected upper limb recovery can be provided.