A Systematic Review and Meta-analysis on the Effectiveness of Transcranial Direct Current Stimulation on Swallowing Function of Poststroke Patients

Dysphagia after stroke: research advances in treatment interventions

After a stroke, most patients have dysphagia, which can lead to aspiration pneumonia, malnutrition, and adverse functional outcomes. Protective interventions aimed at reducing these complications remain the cornerstone of treatment. Dietary adjustments and oral hygiene help mitigate the risk of aspiration pneumonia, and nutritional supplementation, including tube feeding, might be needed to prevent malnutrition. Rehabilitative interventions aim to enhance swallowing function, with different behavioural strategies showing promise in small studies. Investigations have explored the use of pharmaceutical agents such as capsaicin and other Transient-Receptor-Potential-Vanilloid-1 (TRPV-1) sensory receptor agonists, which alter sensory perception in the pharynx. Neurostimulation techniques, such as transcranial direct current stimulation, repetitive transcranial magnetic stimulation, and pharyngeal electrical stimulation, might promote neuroplasticity within the sensorimotor swallowing network. Further advancements in the understanding of central and peripheral sensorimotor mechanisms in patients with dysphagia after a stroke, and during their recovery, will contribute to optimising treatment protocols.

Differential impact of unilateral stroke on the bihemispheric motor cortex representation of the jaw and tongue muscles in young and aged rats

Introduction

Dysphagia commonly occurs after stroke, yet the mechanisms of post-stroke corticobulbar plasticity are not well understood. While cortical activity associated with swallowing actions is bihemispheric, prior research has suggested that plasticity of the intact cortex may drive recovery of swallowing after unilateral stroke. Age may be an important factor as it is an independent predictor of dysphagia after stroke and neuroplasticity may be reduced with age. Based on previous clinical studies, we hypothesized that cranial muscle activating volumes may be expanded in the intact hemisphere and would contribute to swallowing function. We also hypothesized that older age would be associated with limited map expansion and reduced function. As such, our goal was to determine the impact of stroke and age on corticobulbar plasticity by examining the jaw and tongue muscle activating volumes within the bilateral sensorimotor cortices.

Methods

Using the middle cerebral artery occlusion rat stroke model, intracortical microstimulation (ICMS) was used to map regions of sensorimotor cortex that activate tongue and jaw muscles in both hemispheres. Young adult (7 months) and aged (30 months) male F344 × BN rats underwent a stroke or sham-control surgery, followed by ICMS mapping 8 weeks later. Videofluoroscopy was used to assess oral-motor functions.

Results

Increased activating volume of the sensorimotor cortex within the intact hemisphere was found only for jaw muscles, whereas significant stroke-related differences in tongue activating cortical volume were limited to the infarcted hemisphere. These stroke-related differences were correlated with infarct size, such that larger infarcts were associated with increased jaw representation in the intact hemisphere and decreased tongue representation in the infarcted hemisphere. We found that both age and stroke were independently associated with swallowing differences, weight loss, and increased corticomotor thresholds. Laterality of tongue and jaw representations in the sham-control group revealed variability between individuals and between muscles within individuals.

Conclusion

Our findings suggest the role of the intact and infarcted hemispheres in the recovery of oral motor function may differ between the tongue and jaw muscles, which may have important implications for rehabilitation, especially hemisphere-specific neuromodulatory approaches. This study addressed the natural course of recovery after stroke; future work should expand to focus on rehabilitation.

Efficacy of game training combined with surface electromyography biofeedback on post-stroke dysphagia

OBJECTIVE

To explore the efficacy of game training combined with surface electromyography biofeedback (sEMG-BF) in the treatment of dysphagia after early stroke.

METHODS

Ninety patients with early post-stroke dysphagia (PSD), who were diagnosed and treated from March 2021 to December 2022, were divided randomly into a control group (30 cases), experimental group 1 (30 cases) and experimental group 2 (30 cases). The control group received routine swallowing rehabilitation and transcranial direct current stimulation. Experimental group 1 received sEMG-BF in conjunction with the care provided to the control group. Experimental group 2 received sEMG-BF and game training in addition to the care provided to the control group. Before and after treatment, all three patient groups were evaluated using the WADA water swallowing test, the Functional Oral Intake Scale (FOIS), sEMG and a tongue manometer test.

RESULTS

Before treatment, there was no significant difference (P > 0.05) among the three groups of patients in terms of WADA water swallowing rating, FOIS score, submandibular muscle sEMG peak, swallowing time limit and maximum tongue pressure. After treatment, all three groups exhibited improvements in these indices compared with those before treatment (P < 0.05). Experimental group 1 showed greater improvement than the control group (P < 0.05), and experimental group 2 exhibited greater improvement than experimental group 1 and the control group (P < 0.05).

CONCLUSION

Game training combined with sEMG-BF can significantly improve the swallowing function of patients with PSD.

Efficacy of Transcranial Direct Current Stimulation Combined with Conventional Swallowing Rehabilitation Training on Post-stroke Dysphagia

To observe the clinical effects of transcranial direct current stimulation (tDCS) combined with conventional swallowing rehabilitation training on post-stroke dysphagia and explore its long-term efficacy. A total of 40 patients with dysphagia after the first stroke were randomly divided into a treatment group (n = 20) and a conventional group (n = 20). The treatment group received tDCS combined with conventional swallowing rehabilitation training, while the conventional group only received conventional swallowing rehabilitation training. The Standardized Swallowing Assessment (SSA) Scale and the Penetration-Aspiration Scale (PAS) were used to assess dysphagia before and after treatment, at the end of 10 treatments, and at the 3-month follow-up. The changes in infection indicators [the white blood cell (WBC), C-reactive protein (CRP) and procalcitonin (PCT)], the oxygenation indicator [arterial partial pressure of oxygen (PaO2)] and nutrition-related indicators [hemoglobin (Hb) and serum prealbumin (PAB)] were compared before and after treatment. The SSA and PAS scores were lower in both groups after treatment than before treatment, and the difference was statistically significant (P < 0.01). The SSA and PAS scores of the treatment group were lower than those of the conventional group before and after treatment and during follow-up, and the difference was statistically significant (P < 0.05, P < 0.01). A within-group comparison showed that WBC, CRP and PCT after treatment were lower than those before treatment, and the difference was statistically significant (P < 0.05). The PaO2, Hb and serum PAB were higher after treatment than before treatment, with a statistically significant difference (P < 0.05). The WBC, CRP and PCT of the tDCS group were lower than those of the conventional group, and PaO2, Hb and serum PAB were higher in the treatment group than in the conventional group, with a statistically significant difference (P < 0.01). The tDCS combined with conventional swallowing rehabilitation training can improve dysphagia with a better effect than conventional swallowing rehabilitation training and has a certain long-term efficacy. In addition, tDCS combined with conventional swallowing rehabilitation training can improve nutrition and oxygenation and reduce infection levels.

Dosage consideration for transcranial direct current stimulation in post-stroke dysphagia: A systematic review and network meta-analysis

Objective

This systematic review and network meta-analysis sought to determine the efficacy of different intensities of transcranial direct current stimulation (tDCS) in patients with dysphagia after stroke to improve swallowing function.

Methods

Randomized-controlled trials (RCTs) of tDCS in post-stroke dysphagia were searched from Pubmed, EMBASE, Cochrane Library, Web of Science, China National Knowledge Infrastructure (CNKI), Chinese Biomedical Literature Service System (SinoMed), Wanfang database, and Chinese Scientific Journals Database (VIP) from databases' inception to June 22, 2022. Article screening, data extraction, and article quality evaluation were completed by 2 independent researchers. Network meta-analysis was performed using Stata.

Results

A final total of 20 studies involving 838 stroke patients were included. The included control interventions were sham tDCS and conventional therapy (CT). Network meta-analysis showed that 20 min of 1.2, 1.4, 1.5, 1.6, and 2 mA anodal tDCS and 30 min of 2 mA anodal tDCS significantly improved post-stroke dysphagia compared with CT (all P < 0.05). In addition, 20 min of 1, 1.4, 1.6, and 2 mA anodal tDCS also significantly improved post-stroke dysphagia compared with sham tDCS (all P < 0.05). Our results demonstrated that 20 min of stimulation at 1.4 mA was the optimal parameters for anodal tDCS and exhibited superior efficacy to CT [SMD = 1.08, 95% CI (0.46, 1.69)] and sham tDCS [SMD = 1.45, 95% CI (0.54, 2.36)].

Conclusion

Different durations and intensities of anodal tDCS are effective in improving post-stroke dysphagia. However, 20 min of tDCS at 1.4 mA may be the optimal regimen.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/#recordDetails, identifier CRD42022342506.

Assessment and treatment of neurogenic dysphagia in stroke and Parkinson's disease

PURPOSE OF REVIEW

Neurogenic dysphagia worsens quality of life and prognosis of patients with different neurological disorders. Management of neurogenic dysphagia can be challenging. This review provides a comprehensive overview of current evidence on screening, diagnosis, and treatment of neurogenic dysphagia in stroke and Parkinson's disease, suggesting clues for clinical practice.

RECENT FINDINGS

The pros and cons of diagnostic techniques are discussed in the light of updated evidence. Findings from recent meta-analyses of different treatment approaches, including traditional dysphagia therapy, peripheral and central neurostimulation techniques, and treatment with botulinum toxin, are critically discussed, emphasizing inconsistencies and controversial issues.

SUMMARY

Screening tests and clinical swallow examination should be routinely performed in neurological patients at risk for dysphagia. In patients testing positive for dysphagia, first-line instrumental investigations, represented by fiberoptic endoscopic evaluation of swallowing or videofluoroscopic swallow study, should be performed to confirm the presence of dysphagia, to assess its severity, and to inform the treatment. Second-line and third-line instrumental methods can be used in selected patients to clarify specific pathophysiological aspects of oropharyngeal dysphagia. Treatment strategies should be personalized, and combination of traditional dysphagia therapy with innovative treatment approaches may increase the chance of restoring effective and safe swallowing.

Efficacy and Safety of Transcranial Direct Current Stimulation on Post-Stroke Dysphagia: A Systematic Review and Meta-Analysis

Dysphagia is one of the most common symptoms in patients after stroke onset, which has multiple unfavorable effects on quality of life and functional recovery. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation that is widely used to improve deglutition function. Recently, some studies have confirmed that tDCS enhances deglutition function after stroke. However, the number of evaluation indexes used in those studies was small, and the number of trials included was limited. Most importantly, the optimal stimulation protocol is still uncertain and the safety of tDCS has not been reviewed. Therefore, we conducted a systematic review and meta-analysis to address these shortcomings.

METHODS

Seven databases were searched entirely, including Pubmed, Cochrane Library, Web of Science, China National Knowledge Infrastructure (CNKI), Chinese Biomedical Literature Service System (SinoMed), Wan-fang database, and the Chinese Scientific Journals Database (VIP) from inception to 31 December 2021. Two reviewers independently evaluated the eligibility of retrieved data according to the selection criteria and assessed the methodological quality of the studies using the Cochrane risk of bias tool. Outcomes, measures, and indicators used in this study included the dysphagia outcome and severity scale (DOSS), modified Mann assessment of swallowing ability (MMASA), functional oral intake scale (FOIS), functional dysphagia scale (FDS), and Kubota's water-drinking test (KWDT). Sensitivity and subgroup analyses were performed to evaluate the intervention effect more specifically.

RESULTS

Fifteen trials with a total of 787 participants (394 subjects in the tDCS groups were treated with true tDCS, and 393 subjects in the control groups were wait-listed or treated with sham tDCS) involving tDCS for dysphagia after stroke and were included in the meta-analysis. Results of this meta-analysis confirmed that tDCS had a positive effect on post-stroke dysphagia. Subgroup analyses revealed that bilateral and high-intensity stimulation with tDCS had a more significant impact on post-stroke dysphagia. Furthermore, no adverse events occurred during the application of tDCS for post-stroke dysphagia.

CONCLUSION

tDCS can promote the recovery of deglutition function in patients with dysphagia after stroke. In addition, bilateral stimulation and high-intensity stimulation may have better effects. However, the safety evidence for tDCS and post-stroke dysphagia is insufficient.

Role of Catechol-O-methyltransferase Val158Met Polymorphism on Transcranial Direct Current Stimulation in Swallowing

Transcranial direct current stimulation (tDCS) is one of the latest post-stroke dysphagia treatment modalities, and the effect of tDCS is known to be affected by various factors including genetic polymorphisms. However, the role of catechol-O-methyltransferase (COMT) polymorphisms on tDCS in swallowing is unclear. In this prospective pilot study, we aim to explore the effect of tDCS on the swallowing cortex and subsequent swallowing motor function according to COMT polymorphism. Twenty-four healthy participants received either anodal tDCS or sham mode tDCS on the mylohyoid motor cortex at random order, after inhibitory repetitive transcranial magnetic stimulation (rTMS) for preconditioning. The primary outcome was the changes of mylohyoid-motor-evoked potentials (MH-MEP) amplitude in each COMT polymorphism group, from the post-inhibitory rTMS baseline state to immediate, 30, and 60 min after tDCS. The secondary outcomes were the changes in swallowing function. The results showed that COMT Val/Val polymorphism showed improvement across time in the MH-MEP amplitudes and triggering time of swallowing after tDCS, whereas COMT Met carrier group did not show significant changes of MH-MEP or swallowing function across time. This therapeutic response variability of tDCS in the mylohyoid motor system according to COMT polymorphism support the importance of genetic analysis in individualized dysphagia treatment.

Scoping review to identify and map non-pharmacological, non-surgical treatments for dysphagia following moderate-to-severe acquired brain injury

INTRODUCTION

Dysphagia is a common and critical consequence of acquired brain injury (ABI) and can cause severe complications. Dysphagia rehabilitation is transforming from mainly compensatory strategies to the retraining of swallowing function using principles from neuroscience. However, there are no studies that map interventions available to retrain swallowing function in patients with moderate-to-severe ABI.

OBJECTIVE

To systematically map the accessible research literature to answer the research question: Which non-surgical, non-pharmacological interventions are used in the treatment of dysphagia in patients with moderate and severe ABI in the acute and subacute phase? DESIGN: Scoping review based on the methodology of Arksey and O'Malley and methodological advancement by Levac et al. DATA SOURCES: MEDLINE, Embase, Cochrane Library, CINAHL, PsycINFO, Web of Science, OTseeker, speechBITE and PEDro were searched up until 14 March 2021.

ELIGIBILITY CRITERIA

All studies reporting rehabilitative interventions within 6 months of injury for patients with moderate-to-severe ABI and dysphagia were included.

DATA EXTRACTION AND SYNTHESIS

Data was extracted by two independent reviewers and studies were categorised based on treatment modality.

RESULTS

A total of 21 396 records were retrieved, and a final of 26 studies were included. Interventions were categorised into cortical or non-cortical stimulation of the swallowing network. Cortical stimulation interventions were repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation. Non-cortical were complex swallowing interventions, neuromuscular electrical stimulation, pharyngeal electrical stimulation (PES), sensory stimulation, strengthening exercises and respiratory muscle training.

CONCLUSION

This scoping review provides an overview of rehabilitative dysphagia interventions for patients with moderate and severe ABI, predominantly due to stroke, in the acute and subacute phase. Positive tendencies towards beneficial effects were found for rTMS, complex swallowing interventions, PES and cervical strengthening. Future studies could benefit from clear reporting of patient diagnosis and disease severity, the use of more standardised treatment protocols or algorithms and fewer but standardised outcome measures to enable comparison of effects across studies and interventions.