Dysphagia is a common problem in neurologic disease. The authors describe rates of dysphagia in selected neurologic diseases, and the evaluation and treatment of dysphagia in this population. Applicable physiology and aspects of neural control are reviewed. The decision-making process to determine oral feeding versus alternative means of alimentation is examined.
Epidemiology
Dysphagia is common in multiple neurologic diseases ( Table 1 ), particularly in Parkinson’s disease, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Alzheimer’s disease, and, most prominently, in stroke.
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Stroke
Estimates of dysphagia incidence in stroke range between 20% and 90% depending on the method of ascertainment . Conservative estimates of dysphagia incidence in stroke patients suggest that it occurs acutely in about 50% of cases . Dysphagia has been associated with increased stroke mortality, increased hospital length of stay, dehydration, and malnutrition . Stroke patients with dysphagia have an increased risk for aspiration pneumonia (3-fold) . This risk is markedly increased (20-fold) in cases with confirmed aspiration on videofluoroscopy . Aspiration without a cough (silent aspiration) increases the risk of pneumonia and occurs in up to two thirds of stroke patients .
Parkinson’s disease
Up to 77% of Parkinson’s disease patients experience dysphagia . Conservative estimates report a dysphagia incidence of about 50% . Solids have been reported to be more problematic than liquids in Parkinson’s disease patients . Parkinson’s disease patients experience delayed swallowing reflex, prolonged laryngeal movements, and prolonged esophageal phase .
Multiple sclerosis
Dysphagia is not as common in MS. Frequency of dysphagia in MS has been estimated to be between 33% and 43% . De Pauw and colleagues conducted a large study which reported that 29% of patients had swallowing difficulties and 24%, permanent swallowing difficulties . Dysphagia in MS has also been associated with increasing disability , depressed mood, and low vital capacity . Abnormalities observed include impaired oral phase and delayed swallow reflex . Abraham and Yum reported upper esophageal sphincter (UES) dysfunction in all MS patients studied (13 cases) . A 10-item questionnaire for evaluation of dysphagia in MS has recently been developed . This tool allows for overall assessment of dysphagia and characterization of dysphagia to solids or liquids.
Amyotrophic lateral sclerosis
ALS can affect both bulbar and spinal motor systems. Dysphagia occurs at onset in about one third of cases, although generally it occurs late in the disease . ALS severity scales include swallowing as an important factor . Mayberry and Atkinson reported some feeding difficulty in 73% of surveyed patients with motor neuron disease. Dysphagia was reported in 87% of patients who had died of motor neuron disease versus 68% of surviving patients . Aspiration pneumonia rates of 13% have been reported and have been associated with increased mortality (mean survival time postinfection, 2 months) .
Alzheimer’s disease
Swallowing dysfunction in Alzheimer’s disease has been reported extensively, but not many studies have reported the incidence of dysphagia in this population. Horner and colleagues reported that aspiration occurred in 28.6% of Alzheimer’s disease patients studied using videofluoroscopy. Pneumonia is the most common cause of death in this population . Deficits in this population range from oral dysfunction to pharyngeal dysfunction with aspiration. Oral dysfunction is important in this population because it usually leads to eating dependency; a marker for poor outcome and mortality in institutionalized individuals .
Muscular dystrophies
Patients with muscular dystrophy can have a variety of deficits resulting in feeding and swallowing difficulties. Approximately 35% of individuals in a group of patients with myotonic dystrophy, spinal muscular atrophy, facioscapulohumeral muscular dystrophy (FSMD), Duchenne muscular dystrophy (DMD), or limb girdle muscular dystrophy reported problems with at least 1 aspect of feeding .
Patients with DMD have difficulties with mouth opening and chewing that are more frequent as they age and experience choking episodes on average once a week or less frequently . As a result of these problems, patients modify their diet, opting for smaller pieces and softer foods and have increasing mealtime duration . In DMD, the oral phase is affected, and although the pharyngeal phase is timely, it is weak, leaving pharyngeal residue . Videofluoroscopic swallow study (VFSS) has been recommended for asymptomatic DMD patients in their teens because the possibility of dysphagia increases with age . Aloysius and colleagues suggest that for DMD cases with choking, the VFSS is of limited usefulness when compared with a careful feeding regimen.
Oculopharyngeal muscular dystrophy (OPMD) is a disorder among adults that is characterized by bilateral ptosis and dysphagia; it is more common in French Canadians. The overall incidence of OPMD is unclear because it usually manifests itself in the sixth decade of life, and genetic testing was not available until after 1998, when Brais and colleagues determined the specific abnormality in chromosome 14 that causes the disease. Dysphagia in OPMD patients is aggravated by head retroflexion (astrologist’s view), a compensation for ptosis . Cricopharyngeal dysfunction with aspiration is common in OPMD, and treatment with cricopharyngeal myotomy is common .
Dysphagia is not a common symptom of FSMD and was once considered an exclusion criterion . Recent studies suggest that dysphagia occurs in advanced cases of FSMD, but that involvement is mild and seldom life threatening .
Dysphagia is considered one of the most important symptoms of myotonic dystrophy because of its relationship with recurrent pulmonary infections . The prevalence of dysphagia in this population has been reported to be between 25% and 80% . Swallowing dysfunction in myotonic dystrophy is associated with asymmetric pharyngeal contraction and weak UES contraction .
Polymyositis and dermatomyositis
Swallowing dysfunction has been reported in 12% to 54% of patients with polymyositis/dermatomyositis (PM/DM) and is more common in the acute inflammatory phase . The first signs of dysphagia are usually lingual weakness and incoordination . Cricopharyngeal muscle obstruction and esophageal dysmotility are the main abnormalities seen in PM/DM patients, causing aspiration when food backs up into the pharynx . Dysphagia is related to poor prognosis in PM/DM patients. Cricopharyngeal myotomy has been useful in treatment of dysphagia in PM/DM patients, as have corticosteroids given during the acute phase .
Swallowing physiology
Functional swallowing occurs as a result of a series of purposeful movements that allow transport of food from the oral cavity into the stomach while avoiding passage of food into the airway.
Swallowing is divided into 4 stages: (1) oral preparatory—preparation of food for propulsion to the pharynx, (2) oral propulsive—the food is pushed by the tongue through the pharynx, (3) pharyngeal—specific movements transport the bolus to the UES, and (4) esophageal—the bolus is propelled through the esophagus and lower esophageal sphincter to the stomach . The oral preparatory and oral propulsive stages are under volitional control . Once oral propulsion occurs, the following processes are a series of involuntary movements designed to transport the food and protect the airway. Individuals with neurologic disease can have physiologic deficits in any of the swallowing stages.
Oral preparatory stage
The duration of the oral preparatory stage depends on food type and consistency . When food is placed in the mouth, the bite is pulled back, followed by rotational movements of the tongue that place the food in the occlusal surface of the postcanine teeth . Mastication reduces the food to the appropriate consistency for transport.
Oral phase dysfunction can be one of the first signs of dysphagia in neurologic patients. Difficulty in moving food to the pharynx was reported by more than 50% of patients with motor neuron disease . Parkinson’s disease patients develop difficulty in chewing and other oral complaints . Altered feeding habit was the most common complaint in patients with MS .
Oral propulsive stage
When food has been processed and the consistency is appropriate for swallowing, the tongue contacts the hard palate and the area of tongue–palate contact expands posteriorly. This movement squeezes the bolus into the valleculae. Food transport occurs intermittently during processing, allowing for bolus accumulation in the oropharynx before the swallow occurs.
Neurologic disorders that directly affect tongue strength and coordination are more likely to affect oral propulsion. Decreased tongue pressures have been associated with higher incidence of dysphagia . Impaired oral propulsion can result in delayed or absent swallow initiation.
Pharyngeal stage
The pharyngeal phase is a series of highly coordinated events. When the bolus is ready to be swallowed, the soft palate elevates to seal the nasopharynx while the tongue base retracts and the pharyngeal wall contracts to squeeze the bolus downward. Submental muscles contract pulling the hyoid and larynx superiorly and anteriorly and folding the epiglottis backward to seal the laryngeal vestibule. The vocal folds close to seal the glottis and breathing ceases briefly to prevent food inhalation. The cricopharyngeus muscle relaxes to allow for UES opening assisted by contraction of the suprahyoid muscles and the pressure of the descending bolus.
Pharyngeal dysfunction usually occurs later in the course of degenerative neurologic diseases and is associated with increased disease severity. Identifying pharyngeal dysfunction is critical in the prevention of aspiration and subsequent pneumonia.
Esophageal stage
After the bolus passes the UES, peristalsis carries the bolus down to the stomach, assisted by gravity. The lower esophageal sphincter relaxes, allowing bolus passage into the stomach.
Esophageal dysfunction is common is Parkinson’s disease. Abnormalities include delayed transport, stasis, bolus redirection, and tertiary esophageal contractions .
Differences between eating and drinking
During drinking, the oral stage is modified to prevent premature spillage of liquids into the oropharynx. Before swallow initiation, the dorsal tongue is in contact with the soft palate, creating a posterior oral seal . Even in normal individuals, this seal is often incomplete, allowing some liquid to enter the oropharynx. A posterior oral seal is not present in continuous sequential drinking (as in straw drinking), and the liquid usually is at or below the level of the valleculae at swallow onset . Straws may increase the risk of aspiration in patients with an already compromised system due to neurologic disease. It would be a sensible approach to avoid their use in this population unless their safety has been confirmed during instrumental evaluation.
Swallowing physiology
Functional swallowing occurs as a result of a series of purposeful movements that allow transport of food from the oral cavity into the stomach while avoiding passage of food into the airway.
Swallowing is divided into 4 stages: (1) oral preparatory—preparation of food for propulsion to the pharynx, (2) oral propulsive—the food is pushed by the tongue through the pharynx, (3) pharyngeal—specific movements transport the bolus to the UES, and (4) esophageal—the bolus is propelled through the esophagus and lower esophageal sphincter to the stomach . The oral preparatory and oral propulsive stages are under volitional control . Once oral propulsion occurs, the following processes are a series of involuntary movements designed to transport the food and protect the airway. Individuals with neurologic disease can have physiologic deficits in any of the swallowing stages.
Oral preparatory stage
The duration of the oral preparatory stage depends on food type and consistency . When food is placed in the mouth, the bite is pulled back, followed by rotational movements of the tongue that place the food in the occlusal surface of the postcanine teeth . Mastication reduces the food to the appropriate consistency for transport.
Oral phase dysfunction can be one of the first signs of dysphagia in neurologic patients. Difficulty in moving food to the pharynx was reported by more than 50% of patients with motor neuron disease . Parkinson’s disease patients develop difficulty in chewing and other oral complaints . Altered feeding habit was the most common complaint in patients with MS .
Oral propulsive stage
When food has been processed and the consistency is appropriate for swallowing, the tongue contacts the hard palate and the area of tongue–palate contact expands posteriorly. This movement squeezes the bolus into the valleculae. Food transport occurs intermittently during processing, allowing for bolus accumulation in the oropharynx before the swallow occurs.
Neurologic disorders that directly affect tongue strength and coordination are more likely to affect oral propulsion. Decreased tongue pressures have been associated with higher incidence of dysphagia . Impaired oral propulsion can result in delayed or absent swallow initiation.
Pharyngeal stage
The pharyngeal phase is a series of highly coordinated events. When the bolus is ready to be swallowed, the soft palate elevates to seal the nasopharynx while the tongue base retracts and the pharyngeal wall contracts to squeeze the bolus downward. Submental muscles contract pulling the hyoid and larynx superiorly and anteriorly and folding the epiglottis backward to seal the laryngeal vestibule. The vocal folds close to seal the glottis and breathing ceases briefly to prevent food inhalation. The cricopharyngeus muscle relaxes to allow for UES opening assisted by contraction of the suprahyoid muscles and the pressure of the descending bolus.
Pharyngeal dysfunction usually occurs later in the course of degenerative neurologic diseases and is associated with increased disease severity. Identifying pharyngeal dysfunction is critical in the prevention of aspiration and subsequent pneumonia.
Esophageal stage
After the bolus passes the UES, peristalsis carries the bolus down to the stomach, assisted by gravity. The lower esophageal sphincter relaxes, allowing bolus passage into the stomach.
Esophageal dysfunction is common is Parkinson’s disease. Abnormalities include delayed transport, stasis, bolus redirection, and tertiary esophageal contractions .
Differences between eating and drinking
During drinking, the oral stage is modified to prevent premature spillage of liquids into the oropharynx. Before swallow initiation, the dorsal tongue is in contact with the soft palate, creating a posterior oral seal . Even in normal individuals, this seal is often incomplete, allowing some liquid to enter the oropharynx. A posterior oral seal is not present in continuous sequential drinking (as in straw drinking), and the liquid usually is at or below the level of the valleculae at swallow onset . Straws may increase the risk of aspiration in patients with an already compromised system due to neurologic disease. It would be a sensible approach to avoid their use in this population unless their safety has been confirmed during instrumental evaluation.
Neural control of swallowing function
Brain stem
The main center for swallowing control is located in the brain stem. The central pattern generator (CPG) is located in the rostral medulla within the nucleus tractus solitarius and the surrounding reticular formation . The CPG controls 2 main functions: (1) the triggering and timing of the swallowing pattern and (2) the control of motor neurons involved in swallowing . Sensory information to the CPG has been implicated in swallow response modulation and airway protection .
Disruption of the CPG results in severe dysphagia. This is most commonly seen in cases of lateral medullary strokes. It has been suggested that in lateral medullary strokes, swallowing function is globally affected because of an acute disconnection syndrome with the contralateral CPG .
ALS can cause swallowing dysfunction (bulbar ALS) but most commonly dysphagia develops several months after the onset of the disease . Dysphagia in ALS cases is associated with abnormal UES opening, decreased coordination between the laryngeal elevator muscles and the cricopharyngeal sphincter, and a delayed swallow all related to bulbar dysfunction, and progressive corticobulbar degeneration .
Supramedullary control
Several supratentorial structures have been implicated in swallowing control, most prominently the cerebral cortex. The primary motor, motor supplementary, and primary somatosensory cortices (Brodmann areas [BA] 1, 2, 3, 4, and 6) have been implicated in swallowing motor regulation and execution, and sensorimotor control . Other cortical areas have been implicated in swallowing, including the anterior cingulate (BA 24 and 32) , orbitofrontal cortex (BA 10, 11, 12, 44, 45, and 47) , parieto-occipital cortex (BA 7, 17, 18, and 40) , temporopolar cortex (BA 22 and 38) , and insular cortex .
Subcortical structures including the internal capsule , thalamus , basal ganglia , and cerebral peduncles have also been implicated in swallowing control.
Even though the areas previously mentioned have been repeatedly implicated in swallowing control, a comprehensive model integrating the function of supratentorial and bulbar structures has not been described. Future research is necessary to determine how all of these areas integrate to produce functional swallowing.
Dysphagia related to dysfunction of supratentorial structures is the most common type seen in neurologic disease. Dysphagia related to nondegenerative diseases, such as stroke or traumatic brain injury, tends to remain stable or improve with time . In degenerative diseases, dysphagia tends to worsen with time as global brain function deteriorates, interrupting the coordination of the multiple areas involved in swallowing control.
The evaluation of dysphagia in neurogenic disease
Cognitive and communication assessment
In patients with neurogenic disease, before evaluation of swallowing function, it is wise to screen cognitive and communication functioning ( Table 2 ).
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This information will not only affect completion of the clinical swallowing evaluation (CSE) but will also impact the instrumental swallowing evaluation and subsequent treatment. Given the importance of supratentorial modulation of pharyngeal biomechanics, preoral phase deficits, such as decreased attention, may have substantial consequences for oral and pharyngeal swallowing efficiency . The level to which a patient’s cognition and communication are impaired depends on the location and extent of neural damage. A patient with right hemisphere damage or involvement of the parietal or prefrontal lobes is more likely to present with cognitive impairment as compared with the patient with occipital lobe damage. Likewise, a patient with left hemisphere damage is more likely to have aphasia than a person with right hemisphere damage.
Recent research has supported the notion that neglect is associated with dysphagia. Neglect is defined as failure to respond or orient to stimuli presented to the contralesional side in the presence of intact elemental sensory and motor functioning . Neglect may be spatial or personal and is evidenced by sensory inattention, motor intention, spatial neglect, and/or unawareness of deficits. Parker and colleagues reported that fewer than half of acute stroke patients were aware of their dysphagia symptoms (eg, coughing, drooling). Most of the patients who were diagnosed with dysphagia and were aware of symptoms did not acknowledge having a “swallowing problem.” Patients with poor awareness of their dysphagic symptoms did not modify swallowing behavior, whereas patients who were aware of their dysphagia modified rate and volume of ingestion. Moreover, patients with poor awareness developed more medical complications at 3 months post-onset as compared with the group with good awareness of dysphagia symptoms. Spatial neglect has been associated with initial non-oral intake in acute stroke patients , and rehabilitation of dysphagia is longer in patients with neglect .
The clinical bedside swallowing evaluation
In patients with complaints of dysphagia or those patients with neurogenic disorders associated with a high frequency of dysphagia, a clinical bedside swallowing evaluation (CSE) should be completed. From the CSE, one can determine which patients warrant an instrumental examination, develop a hypothesis of the underlying swallowing pathophysiology, and develop plans concerning a management program. The CSE generally includes an examination of oral structural integrity, cranial nerve function, and swallowing.
Notation is made of the appearance of oral mucosa in terms of salivation and color. Pooling of saliva in the oral cavity generally does not indicate hypersalivation in patients with neurogenic disease; rather, it may indicate dysphagia. Dentition should be evaluated in terms of the number and appearance of the teeth, and the presence or absence of a dental prosthesis. Poor dental care in combination with decreased mobility, sensation, and awareness of dysphagia may increase the risk of pneumonia in stroke patients. Dental decay and dependence for oral care are significant contributors to the development of aspiration pneumonia .
A thorough cranial nerve examination will allow inference of potential swallowing pathophysiology. Evaluation of motor and sensory integrity of the face, lips, tongue, and palate will allow the examiner to link clinical observations of cranial nerve impairment with suspected oropharyngeal pathophysiology and thereby increase sensitivity for detecting dysphagia on the CSE .
The swallowing portion of the CSE includes administration of various consistencies (liquids, semi-solids, solids) and volumes over multiple trials. It is generally best to start the examination with small volumes of thin liquids to reduce the amount of aspiration, should it occur, and to prevent contaminating the pharynx with residue from a thicker consistency. In some patients, particularly those who have been without oral intake for a period of time or those with significant cognitive deficits, it may be wise to start by having the patient chew and swallow ice chips to “prime” the swallowing system and direct the patient’s attention to the swallowing task.
From the CSE, particular features have been identified to determine which stroke patients are at risk for aspiration and warrant an instrumental examination. This is important, particularly after an acute stroke, as all patients may not warrant an instrumental examination. However, it should be noted that much of this focus is directed to identification of patients with risk of aspiration, not with risk of dysphagia. Many patients with neurologic disease may present with dysphagia without aspiration. Early studies relied on the presence of a cough or voice change after ingestion of 3 oz of water to determine aspiration. Poor sensitivity, however, has decreased the usefulness of an isolated water swallow test, as the risk of false-negative results is high .
A cluster of symptoms and signs of aspiration in addition to coughing or voice change after swallowing have been evaluated in acute stroke patients to increase the ability to detect silent aspiration in acute stroke. Six clinical features (dysphonia, dysarthria, abnormal volitional cough, abnormal gag reflex, cough on trial swallow, and voice change on trial swallow) were associated with risk of aspiration (residual material in the larynx or aspiration) as identified using videofluroscopy . The presence of any 2 of these 6 clinical features correctly identified risk of aspiration with 92% accuracy . Studies by other investigators have confirmed the usefulness of these 6 clinical features in the identification of risk of aspiration in acute stroke patients but have suggested that the presence of 4 clinical predictors increases specificity . Others have indicated that the presence of 2 of these 6 features identified by Daniels and colleagues . was not strongly related to aspiration as identified by endoscopic evaluation . Contradictory findings may be related to different outcome measures, evaluation type, and evaluation protocol. Overall, research suggests that clinicians can rule in aspiration when it is truly present but that ruling out aspiration when it is absent is difficult to do .
Dysarthria may correlate with dysphagia in individuals with bulbar ALS. Individuals with ALS may not complain of dysphagia but may evidence reduced speech intelligibility. Progression of dysphagia parallels the progression of speech intelligibility in ALS . Furthermore, dysphagia increases as respiratory capacity decreases regardless of the form of ALS . As such, vital capacity should be consistently measured. Accurate and timely assessment of a clinically relevant decline in respiratory status seems crucial for determining the timing of feeding tube placement.
Instrumentation, such as pulse oximetry and cervical auscultation, has been added to the CSE to increase sensitivity and specificity. With pulse oximetry, oxygen saturation is measured before, during, and after swallowing, with decrease in saturation during and after swallowing purported to be associated with aspiration. Contradictory findings; however, have been reported, with some studies indicating a strong correlation between desaturation and aspiration , whereas others have shown poor association . Such discrepancies may be attributed to the desaturation criteria and to the lack of an instrumental evaluation to confirm aspiration. Cervical auscultation is used to amplify either swallowing sounds or airway sounds during direct oral intake. Generally, a simple stethoscope is used, but a microphone or accelerometer may be added for improved fidelity and signal recording. Recent research identified reduced reliability among raters, which in turn yielded reduced ability to distinguish between stroke patients with and without aspiration . Until reliability is established for cervical auscultation and pulse oximetry, neither adjunct can be assumed to provide additional value to the CSE.
Instrumental evaluation
The purpose of an instrumental swallowing study is to evaluate physiologic functioning of the oropharyngeal swallowing mechanism, determine swallowing safety, and identify the effects of compensatory strategies, such as posture and bolus consistency, on deglutition. By determining the exact cause of dysfunction, therapeutic intervention can be initiated to address the specific disorder. The 2 primary instrumental tools used to evaluate oropharyngeal dysphagia are VFSS and videoendoscopy. The advantages and disadvantages of each are listed in Table 3 . As neurogenic dysphagia can impair all 3 stages of swallowing, VFSS is the preferred instrumental assessment tool for the neurogenic population. However, medical diagnosis and results from the cognitive evaluation and CSE may dictate which examination is done. For example, videoendoscopy may be useful in the evaluation of swallowing in patients with specific diagnoses, such as myasthenia gravis, in which dysphagia occurs with fatigue, or in patients with contractures, for whom positioning during the VFSS is suboptimal.
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