Electromyography biofeedback training for post-stroke dysphagia

Abstract

Dysphagia is a common complication of ischemic stroke and is usually difficult to treat. The mainstay of standard therapy of post-stroke dysphagia (PSD) is effortful swallowing. Since its introduction in 2004, there is increasing evidence that surface electromyography-guided biofeedback training (EMGBT) can enhance the therapeutic effect of standard LE. In this editorial, we comment on the article by Meng et al published in the recent issue of the World Journal of Clinical Cases, which provided evidence that particularly extensive EMGBT with an increased number of sessions is definitively more effective than the standard speech therapy or ordinary EMGBT. Among the 90 PSD patients with ischemic stroke or intracerebral bleeding, those who underwent EMGBT in more sessions than usual particularly benefited from the approach. It was concluded that EMGBT is more effective than traditional swallowing training in improving dysphagia and swallowing disorders as well as hyoid-laryngeal complex movement speed in PSD patients.

Key Words: Ischemic stroke; Dysphagia; Electromyography; Biofeedback; Rehabilitation

Core Tip: A previous case study published in the World Journal of Clinical Cases demonstrated significant improvements in post-stroke dysphagia (PSD) using electromyography biofeedback training, emphasizing its potential as an effective treatment modality. The study showed that intensive surface electromyography-guided biofeedback training (EMGBT) can improve swallowing function in PSD patients more effectively than conventional speech therapy. For this reason, comprehensive EMGBT has been recommended as an adjuvant treatment for dysphagia in PSD patients.

INTRODUCTION

Dysphagia is the inability to move food safely and effectively into the stomach due to structural or functional impairment of the jaw, lips, tongue, soft palate, pharynx, or esophagus[1]. Depending on the location of the lesion, dysphagia is divided into oro-pharyngeal (proximal) dysphagia and esophageal (distal) dysphagia[1]. Oropharyngeal dysphagia manifests as difficulty initiating swallowing, coughing, choking, or aspiration and is most commonly caused by chronic neurological diseases such as ischemic stroke, Parkinson disease, or dementia[1]. Esophageal dysphagia is characterised by the feeling that food gets stuck after swallowing, most commonly caused by gastroesophageal reflux disease or functional esophageal disorders[1].

Dysphagia after ischemic stroke, also known as post-stroke dysphagia (PSD), is usually oropharyngeal in nature and is a common complication of ischemic stroke, often leading to adverse outcomes due to chronic aspiration and subsequent pulmonary infections, as well as inadequate nutrition and inadequate intake of calories, electrolytes, vitamins, and trace elements as well as inadequate fluid intake[2]. PSD may be due to involvement of numerous cerebral structures[3]. Structural and functional imaging studies have shown that PSD results from impairment of the sensorimotor cortex, insula, cerebellum, cingulate gyrus, thalamus, basal ganglia (e.g., lentiform nucleus), and associated white matter connections, or the brainstem[3]. About 40% of patients with acute ischemic stroke develop PSD, but the prevalence figures of PSD vary significantly between studies with estimates ranging from 8% to 80%[4]. About half of patients with PSD are still affected six month after stroke[4].

The most commonly used treatment options for PSD include dietary adjustments and oral hygiene to help mitigate the risk of aspiration pneumonia, nutritional supplementation including tube feeding, use of pharmaceutical agents such as capsaicin and other transient receptor potential vanilloid-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, and the effortful swallowing (ES) technique, which relies on the use of maximum voluntary effort to behaviorally alter aspects of swallowing physiology[5,6]. However, it remains uncertain whether all patients with PSD can actually maximally recruit muscle activity during exercise and whether age and bolus type have an influence on performance[2]. In a study of healthy subjects, it was shown that swallowing with maximal effort resulted in increased amplitude and prolonged duration of the electromyography (EMG) interference pattern recorded via surface electrodes (sEMG) from submandibular muscles, while swallowing with minimal effort led to a reduced sEMG interference pattern amplitude without a change in sEMG signal duration[6]. These findings supported the concept of swallowing as a submaximal task and suggested the development of sEMG biofeedback techniques for rehabilitation[6].

Biofeedback is a therapy method that is based on measuring and amplifying body signals that are not consciously perceptible and then returning them to consciousness as perceptible stimuli (visual, acoustic)[7]. Biofeedback is generally used to train patients' self-control over psychosomatic processes. Biofeedback can be used to improve health, performance, and physiological changes that often occur associated with changes to thoughts, emotions, and behavior. sEMG allows both a patient and the clinician to have direct and immediate access to muscle function that is not possible through manual palpation or visual observation[7]. sEMG biofeedback training (EMGBT) can be used to train down increased muscle activity or up train weak, inhibited, or paretic muscles[7]. EMGBT can be also used to differentiate between dysphagia and odynophagia (dysphagia associated with pain)[8].

Several studies have now been carried out that show a positive effect of EMGBT for the treatment of PSD[9-15]. In a study of 25 PSD patients compared with 20 patients with dysphagia after treatment for head/neck cancer, it was shown that 92% of stroke patients and 80% of head/neck cancer patients improved their functional oral intake of foods and liquids using EMGBT[9]. Patients in the stroke group completed more therapy sessions thus increasing the overall cost of therapy, but made greater functional gains, resulting in a lower cost per unit of functional change, than patients in the head/neck cancer group[9]. In a study of 11 PSD patients [tube-dependent (n = 8), oral diet (n = 3)] with an average onset of dysphagia at 31 months, the functional oral intake scale (FOIS) increased from 2.6 to 5.6 after an average of seven treatment sessions within 76 days[10]. In 6 of the 8 tube-dependent patients, percutaneous enteral gastrostomy tubes could be removed after treatment[10]. Bogaardt et al[10] concluded that EMGBT could be an effective complementary standard therapy in the treatment of chronic PSD. EMGBT can be also used to assess the effect of neuromuscular electrical stimulation (NMES) in PSD patients[11]. In 10 PSD patients who received NMES 30 minutes a day, five times a week, and for 4 weeks, video-fluoroscopic dysphagia score (VDS) and penetration-aspiration scale (PAS) improved from 13.4 to 9.4 in the oral phase and from 38.4 to 20.7 in the pharyngeal phase[11]. The PAS also improved from 5.1 to 2.7 when comparing the condition before and after the procedure[11]. The authors concluded that NMES monitored by sEMG can be used to improve oropharyngeal swallowing in PSD patients[11]. In a randomised controlled trial with 17 PSD patients, nine of whom received EMGBT and eight PSD patients received control treatment, it was found that FOIS improved in all patients regardless of the type of treatment used[13] and that EMGBT, in particular, improved pharyngeal clearance and swallowing safety and that these effects remained stable over a period of two months[13]. The authors concluded that EMGBT is an effective rehabilitation technique for PSD patients, especially for improving pharyngeal clearance and swallowing safety, thereby reducing the risk of aspiration and malnutrition[13]. However, when comparing the effect of EMGBT with visual video-fluoroscopy biofeedback on the accuracy of airway protection during swallowing during training of the voluntary laryngeal closure (vLVC) swallowing manoeuver in 19 PSD patients, it was found that both the accuracy of vLVC training performance and clinical feedback accuracy were poorer in patients who underwent EMGBT compared to patients who underwent visual video-fluoroscopy biofeedback[12]. It was concluded that airway protection during swallowing requires precisely timed movements of small, hidden laryngeal and pharyngeal structures and that kinematic biofeedback using video-fluoroscopy may be needed to ensure that targeted swallowing movements are trained during rehabilitation and not maladaptive movements[12].

Shortcomings of the sEMG are that the signal-to–noise ratio can be low depending on the placement of the electrodes, the amount of subcutaneous fat, the extent of muscle edema, the extent of muscle wasting, and the type of electrodes. Furthermore, the recorded interference pattern strongly depends on comorbidities and co-medications that affect the recruitment of motor units, motor nerve functions, the neuromuscular endplate, and muscle fibre conductivity. Therefore, patients with cerebral or spinal cord disease that affect the recruitment, illnesses of cranial nerves IX X, and XII, transmission disorders such as myasthenia or myasthenic syndrome, and all types of muscle disease, may heavily influence the shape and quality of the recordable interference pattern.

In their study, Meng et al[16] aimed to investigate the effect of EMGBT on swallowing function and motor speed in 90 PSD patients. They divided the 90 patients into three groups, one group (n = 30) received routine speech therapy (ES) only (group-1), a second group (n = 30) received ES plus EMGBT (group-2), and a cohort of 30 PSD patients additionally received two training sessions with EMGBT (group-3)[16]. They evaluated the effect of these three types of treatment using the swallowing disorder score (VGF), the Rosenberg PAS, the standard swallowing assessment (SSA), and the VDS before starting therapy and four weeks later, in which the therapies were applied[16].

Only patients with a confirmed diagnosis of ischemic stroke or intracerebral bleeding clinically were included, presenting with dysarthria, aphasia, difficulty chewing or swallowing, choking when drinking water, dyskinesia of the soft palate, pharyngeal muscles, tongue, masticatory muscles, or the facial muscles, tongue atrophy, tremor, diminished or absent gag reflex, diminished or absent soft palate reflex, exaggerated masseter reflex, or abnormal brainstem reflexes[16]. Inclusion criteria were first stroke, informed consent, alertness and stability, and the absence of severe cognitive dysfunction or aphasia[16], Patients with severe mental or physical illnesses that made collaboration impossible, malignancies, previous throat or neck treatments, and metal internal fixation were excluded[16].

Meng et al[16] found no difference between the three groups in PAS and VGF scores before treatment. After four weeks of treatment, both SSA and VGF had improved in all three groups[16]. When the results were compared between the three groups, it was found that the therapeutic effect measured using the PAS was highest in group-3 patients, but VGF scores were not different between the three groups[16]. Likewise, there was no difference in the forward or upward movement speed of the hyoid bone between the three groups before treatment. However, after four weeks of treatment, the forward and upward movement speed of the hyoid bone had increased in all three groups[16]. When comparing the three groups, the forward and upward movement speed of the hyoid bone was increased in group-2 and group-3 compared to group-1 patients[16].

A limitation of the study is that patients with ischemic stroke and intracerebral bleeding were mixed. Because the prognosis and outcome can vary significantly between the two, only patients from one of the two diagnostic cohorts should be included in a study of the effect of EMGBT in PDS patients. Since the effect of EMGBT can also depend heavily on the anatomical location of the stroke, it is recommended to examine PSD patients with similar or the same location and stroke volume.

CLINICAL IMPLICATIONS

EMGBT can be used as an important supplementary measure for PSD. The more intensively this method is used, the better the recovery from PSD.

CONCLUSION

EMGBT is more effective than traditional swallowing training (e.g., ES) in improving dysphagia and swallowing disorders and in increasing the movement speed of the hyoid-laryngeal complex in PSD patients. Clinicians should recognise that the EMGBT can be a useful, complementary method for treating PSD patients and improving their outcome.