Rehabilitation of Lower Cranial Nerve Dysfunction

Rehabilitation of Lower Cranial Nerve Dysfunction Timothy D. Anderson, MD, Eva Michalakis, CCC-SLP, and Peter Catalano, MD Lower cranial nerve dysfunction can be attributed to a variety of causes and may result in severe morbidity and even mortality. Immediate problems are primarily related to difficulty with swallowing and resultant aspiration pneumonia. Voice problems typically are less dangerous but can affect quality of life adversely. With appropriate diagnosis of these deficits, management and rehabilitation can prevent serious complications. Although many lower cranial nerve deficits can be treated adequately by speech and swallowing therapy alone, surgical rehabilitation of these deficits is sometimes required to obtain optimal functional outcomes. Oper Tech Neurosurg 8:50-53 © 2005 Elsevier Inc. All rights reserved. KEYWORDS swallowing, voice, lower cranial nerve dysfunction, complications

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ower cranial nerve deficits are an infrequent but severe complication of neurosurgical procedures, strokes and other disorders. The lower cranial nerves must be intact for the voice and swallowing to be normal. Deficits can lead to dysphagia, voice disorders, aspiration pneumonia, and even death. Accurate diagnosis of the presence and extent of lower cranial nerve deficits is essential to avoid serious complications. We briefly review the physiology of voice and swallowing and provide an approach to the management of voice and swallowing problems related to lower cranial nerve deficits.

Physiology of Swallowing Swallowing is a complex process involving sensory and motor components of structures in the oral cavity, pharyngeal cavity, and esophagus. The goal of this series of sequential neuromuscular events is to transport food, liquid and saliva from the mouth into the stomach safely and efficiently. The swallow is typically divided into four stages: the oral preparatory stage, the oral stage, the pharyngeal stage, and the esophageal stage. The oral preparatory phase involves entry of food or liquid into the oral cavity and includes mastication or mixture with saliva to form a cohesive bolus. A successful oral preparatory phase requires tongue coordination and strength (hypoglossal nerve, CN XII), tension in the cheeks and lips (facial nerve, CN VII), intact oral and oropharyngeal sensation (trigeminal, CN V; glossopharyngeal, CN IX) and jaw motion (CN V). Edentulous patients are able to prepare food, as are those with restricted jaw motion or reduced buccal retention Department of Otolaryngology—Head and Neck Surgery, Lahey Clinic, Burlington, MA Address reprint requests to Timothy D. Anderson, M.D., Department of Otolaryngology—Head and Neck Surgery, Lahey Clinic, 41 Mall Road, Burlington, MA 01805. E-mail: [email protected]

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1092-440X/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.otns.2005.07.001

and lip closure. However, normal tongue mobility or adequate tongue mobility is necessary and is actually the most important neuromuscular function involved in the oral preparatory phase. Transition from the oral preparatory stage to the oral phase begins as the tongue moves posteriorly and pushes the formed bolus against the hard palate.1 The bolus is then prepared for propulsion through the oral cavity. Retraction of the base of tongue is essential for propulsion of the bolus into the pharynx. In normal patients the oral stage lasts no longer than one second and does not vary significantly with age or sex.2,3 Recent studies have shown that the consistency and size of the bolus may alter the timing of the various stages of the swallow.4 The first two stages of the swallow are entirely voluntary. As the food bolus passes into the pharynx, the reflexive portion of swallowing is triggered via glossopharyngeal nerve (CN IX) afferents. Their activation causes several simultaneous physiological activities to occur in the larynx and pharynx: Velopharyngeal closure; laryngeal elevation; inversion of the epiglottis, closure of all laryngeal sphincters (aryepiglottic folds, false vocal folds, and true vocal folds), initiation of pharyngeal peristalsis (squeezing), and relaxation of the upper esophageal sphincter.5 The food bolus is pushed through the pharynx, around the closed larynx, through the open upper esophageal sphincter, and into the distal esophagus.6 During the esophageal stage, the food bolus is moved down the esophagus and into the stomach by coordinated esophageal muscular contraction. Once the esophageal phase is initiated, the upper esophageal sphincter closes, preventing reflux of the bolus back into the pharynx.

Physiology of Speech Normal voice depends on complex interactions among the power source (lungs, diaphragm and abdominal/chest muscles), the vibratory source (vocal folds), and the resonators

Rehabilitation of lower cranial nerve dysfunction (upper aerodigestive tract, tongue and lips). Word formation requires precise motions of the tongue and lips as well as interaction with airflow through the larynx. Although interruptions in any of these systems can cause problems with communication, the most important portions for intelligible speech are the larynx (CN X) and tongue (CN XII).

CN IX The CN IX is efferent to one muscle only, the stylopharyngeus. This muscle dilates the pharynx laterally and contributes to the elevation of the pharynx and larynx. Efferent secretomotor fibers to the parotid glands stimulate production of saliva, which is important in bolus formation. Special sensory fibers carry taste information from the posterior third of the tongue. The most important physiologic action of CN IX is carrying sensation from the upper pharynx, which typically triggers the swallow reflex. Fortunately, in patients with glossopharyngeal injuries, a secondary, vagal-mediated reflex can trigger a swallow. CN IX mediates the sensory portion of the pharyngeal gag; therefore, the best indication of a reduced function is reduced or absent gag sensation. A more sensitive test than simple presence of palatal elevation with posterior pharyngeal stimulation is to compare patient perception of gag intensity with identical stimuli to the left and right sides of the oropharynx. Gag reflexes have been reported to be absent in as many as 13% of normal subjects.7,8 For this reason, the presence or absence of a gag reflex is not a good prognostic indicator of swallowing ability or function. The gag reflex is a protective mechanism and is not necessary to swallow adequately.

CN X CN X is involved in multiple steps in both swallowing and speech. The vagal sensory fibers provide a “backup” system to trigger the swallow reflex, albeit at a later stage than the normal glossopharyngeal trigger. The most important functions of the vagus are in its muscular efferents. The vagus supplies the pharyngeal constrictors that propel the food bolus down toward the esophagus. Peristaltic contractions begin superiorly and move inferiorly. Disruption of the muscle contractions may result in pharyngeal coating and residue and consequently can result in aspiration. CN X also inhibits the normal tonic contraction of the upper esophageal sphincter, allowing this valve to relax and the food bolus to pass into the esophagus. Finally, CN X innervates the intrinsic laryngeal musculature, stimulating laryngeal closure during swallow to prevent aspiration. Vagal stimulation also closes the vocal folds for speech and opens them for respiration. Patients with unilateral vagal injury present with a very breathy, hoarse voice, and coughing on swallow. Specialized testing may show a unilateral laryngeal sensory deficit.9 Bilateral injuries tend to be associated with a swallow function. More importantly, they often appear as respiratory insufficiency and stridor related to the inability to abduct the vocal folds and open the larynx for respiration. Tracheotomy is frequently required for airway management in patients with bilateral injuries. The upper esophageal sphincter may fail to relax with vagal injuries, exacerbating the swallowing dysfunction.

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CN XII CN XII primarily provides efferent innervation of the intrinsic tongue musculature. The tongue is muscle covered by a thin layer of mucosa; therefore, muscular fibrillations can frequently be observed after denervation. Muscular atrophy is a late finding. The tongue will deviate to the side of injury on protrusion. The patient with unilateral hypoglossal nerve injury typically becomes symptomatic with dysarthric, muffled speech and may have swallowing difficulties, especially during the oral preparatory and oral phases. Bilateral injuries are devastating and can cause significant communication and swallowing dysfunction. Tongue mobility is the most critical component of swallowing initiation, especially in the triggering of the pharyngeal stage. The presence of food alone is not an adequate stimulus to trigger the pharyngeal phase of swallowing.

Speech and Swallowing Rehabilitation Detecting the presence or absence of a swallowing impairment is insufficient. To successfully rehabilitate the swallowing function, the reason underlying the impairment must be identified. Aspiration may be caused by a variety of defects, in most cases by a breakdown in a combination of the synergistic components of the swallow. For example, an impaired ability for the base of tongue to contact the posterior pharyngeal wall may decrease the generation of pharyngeal pressure and lead to pharyngeal stasis and aspiration after the swallow. Delayed initiation of the swallow may result in aspiration before the swallow reflex even begins. Early involvement of a speech-language pathologist is essential to obtain an accurate diagnosis and management of swallowing impairment. Specialized testing, including radiologic imaging and endoscopic examination, is frequently required. Flexible endoscopic evaluation of swallowing with sensory testing provides vital information about laryngeal sensation, the mechanics of swallowing, and the risk of aspiration (Fig. 1). It also enables trials of compensatory strategies under direct observation. The goal of dysphagia therapy is safe and efficient swallowing function. Ideally, patients return to an exclusively oral diet with adequate nutrition and the benefits of the psychosocial aspects of eating. In certain cases, especially those with cognitive impairments or bilateral or multiple nerve injuries, this goal is unrealistic. In these cases appropriate, safe, swallowing goals must be identified and therapy will be directed toward these goals. It is often possible for a patient with severe swallowing dysfunction to safely use recreational oral intake while maintaining nutrition via a feeding tube. Rarely, no oral intake is possible for a particular patient, and ablative surgery must be considered to prevent chronic aspiration. A dysphagia therapy program may include compensatory strategies such as postural changes, dietary modifications, or use of swallowing techniques to improve airway protection and bolus transport. For example, the goal of rehabilitative exercises for oromotor function is to improve lingual or labial strength and range of motion. Such exercises are often successful in treating patients with dysarthria, a diminished ability to form an oral bolus, and

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T.D. Anderson, E. Michalakis, and P. Catalano

Figure 1 Example of severe silent aspiration as noted on flexible endoscopic evaluation of swallowing with sensory testing. In the initial examination, before administering food, the vocal folds both (A) abduct and (B) fully adduct, completely sealing the laryngeal inlet. Note the large quantities of thick, sticky mucous in the piriform sinuses. The presence of retained mucous frequently indicates both a sensory deficit and poor pharyngeal clearance, often related to poor pharyngeal muscle contractility. (C) The result of orally presenting a teaspoonful of green-dyed puree. The material immediately penetrates into the laryngeal inlet and is aspirated because the patient cannot sense the presence of the bolus on the vocal folds. Patients with severe sensory deficits are at high risk of aspiration pneumonia even if the remainder of the swallow is completely normal. This patient, who also has poor pharyngeal squeeze, should consider short-term enteral nutrition with potential further swallow rehabilitation as an outpatient. (Color version of figure is available online.)

impaired transit. Push-pull exercises and a variety of breath-holding strategies can improve both speech and swallow after a vagal injury. Thickening liquids can help delay aspiration in patients with glossopharyngeal dysfunction by allowing the intact vagus to trigger a swallow reflex before aspiration occurs.

Surgical Rehabilitation of Speech and Swallowing Unfortunately, in many cases speech and dysphagia therapy alone are ineffective treatment and surgical procedures must be considered for rehabilitation. Patients with unilateral, isolated vagal nerve injuries are excellent can-

didates for surgical rehabilitation. In the short term, vocal fold injections of gelfoam or collagen can augment the paralyzed vocal fold, improving glottic closure and decreasing the risk of aspiration.10 Improved glottic closure has the secondary benefit of markedly improving cough strength, allowing efficient clearance of aspirated boluses and better pulmonary toilet. Injection laryngoplasty can be performed in the office or at the bedside in cooperative patients or in the operating room if necessary.10 Permanent medialization with injections of hydroxyapatite or autologous fat or surgical augmentation with a variety of materials is typically deferred for at least 6 months if there is any hope of nerve recovery.11 Bilateral vagal nerve injury can manifest with respiratory distress and stridor or with severe swallowing dysfunction and inadequate voice and

Rehabilitation of lower cranial nerve dysfunction cough, depending on the position of the vocal folds. Many patients with bilateral vocal fold paralysis require a tracheotomy for the airway protection and pulmonary toilet. Ablative procedures to improve airway can be considered in the long term to allow tracheotomy decannulation. However, the risk is worsening the voice and swallowing. Other surgical procedures are available to treat specific deficits in swallowing. For example, incomplete relaxation of the upper esophageal sphincter can be abolished by cricopharyngeal myotomy. Laryngeal elevation procedures are commonly performed at the same time to prevent overflow aspiration and to allow the swallowed bolus time to pass into the esophagus. Sensory re-innervation of the pharynx and larynx is in its infancy but offers some hope for patients with aspiration from a desensate pharynx and larynx.12 Although a tracheotomy may improve pulmonary toilet and be advisable for a variety of reasons in this patient population, the presence of a tracheotomy usually worsens swallow function because of loss of sensation, laryngeal fixation and ineffective cough. In patients with intractable aspiration, ablative procedures such as narrow field laryngectomy, cricotracheal separation and epiglottic tube procedures may be considered. Technically, some of these procedures are reversible. However, few patients with such severe swallowing dysfunction recover enough function to make reversal advisable. Finally, enteral nutrition via an NG, G-tube, or J tube must always be considered in patients with dysphagia for short- or long-term maintenance of adequate nutrition. Enteral access can always be discontinued if swallowing improves.

Conclusion Accurate diagnosis is essential in the rehabilitation of speech and swallowing deficits related to lower cranial nerve injury.

53 Early involvement of speech-language pathologists helps ensure safe nutrition. Surgical rehabilitation of these deficits is sometimes helpful, especially for unilateral vagal injuries. Prompt otolaryngological consultation is needed for patients with intractable aspiration, respiratory problems or suspicion of bilateral vagal injuries. Enteral access and feedings should always be options for patients with swallowing dysfunction.

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