9 Cranial Nerves IX, X, XII: Dysphagia
Abstract
Intact motor and sensory function of cranial nerves IX (glossopharyngeal), X (vagus), and XII (hypoglossal) are paramount to a normal voice and swallow. Paralysis of one or all of these cranial nerves can lead to hoarseness, taste and sensory disturbances, and dysphagia/aspiration, affecting all phases of swallowing to varying degrees. Pain in the head, neck, face, and oral cavity can be another symptom. Multiple cranial neuropathies such as these can be life-threatening and difficult to treat. History and physical examination typically confirm the diagnosis of paralysis of these nerves with the etiology typically due to pathology in the lower brainstem, skull base, or extracranial course of the nerves. Workup includes imaging of the brain, brainstem, skull base, and neck in addition to swallowing studies. Treatment is based on etiology and severity of symptoms. Regardless of treatment, all of these patients will require speech and swallowing therapy and some will possibly require a percutaneous gastrostomy and/or tracheostomy.
9.1 Normal Swallowing Mechanism
The act of swallowing is a complex coordination of events that relies on intact sensory and motor input and intact structures. Cranial nerves V, VII, IX, X, and XII are involved in a normal swallow. There are four phases of swallowing: oral preparatory, oral, pharyngeal, and esophageal. The oral preparatory and oral phases are voluntary and the pharyngeal and esophageal phases are involuntary. In the oral preparatory phase of swallowing, the food is mixed with saliva and chewed, using the lips, cheeks, muscles of mastication, and tongue. The bolus is prepared and voluntarily moved by the tongue posteriorly to the pharynx. The pharyngeal phase is initiated when the bolus reaches the faucial arches and is triggered by the superior laryngeal nerve. The following occurs during the pharyngeal phase: respiration stops, the soft palate elevates to contact the posterior pharyngeal wall preventing material from entering the nasal cavity, the larynx elevates and glottic closure occurs at all three sphincters (epiglottis/aryepiglottic folds, false vocal cords, and true vocal cords), contraction of the constrictor muscles occur moving the bolus forward, and relaxation of the cricopharyngeus muscle allowing the bolus to enter into the esophagus and finally the stomach.
9.2 Initial Workup
Most patients with swallowing disorders typically present to their primary care physician complaining of choking with foods. The first test for suspected dysphagia should be a modified barium swallow ($220). If aspiration is suspected with signs of fever and cough, a posteroanterior (PA) and lateral chest X-ray may also be obtained ($30) prior to the swallow study to evaluate for aspiration pneumonia or pneumonitis. Following the initial evaluation, the patient should be referred to an otolaryngologist. If a devastating neurologic disorder or neoplasm is suspected, referral should be made immediately.
9.2.1 Symptoms
Patients presenting with paralysis of cranial nerves IX, X, and XII typically report change in taste, severe dysphagia to both solids and liquids including difficulty forming and moving the food bolus toward the pharynx, aspiration with liquids with possible history of pneumonia, and nasal regurgitation. Changes in verbal speech include breathy dysphonia (change in voice quality) and dysarthria (speech not well articulated). These symptoms are due to lack of both motor and sensory inputs with decrease sensation palate, pharynx, larynx, and esophagus. Dyspnea on exertion and weakened cough due to loss of positive end expiratory pressure (CN X palsy) can contribute to the poor overall status of these patients, including weight loss. 1
9.2.2 History
Evaluation of every patient should begin with a thorough history. The physician needs to ascertain the following: the duration and progression of symptoms; any precipitating event; recent history of head and neck trauma or surgery; personal or family history of genetic, neuromuscular, or connective tissue disorders; history of muscle weakness; history of head and neck cancer, and history of tobacco and alcohol use. The most common causes of multiple lower cranial nerve palsies are trauma to the skull base, tumors of the skull base, and neuromuscular disorders. 1 While interviewing the patient, attention is paid to the quality of his or her voice and speech. The voice may be breathy, particularly with a high vagal lesion, and difficult to project. It may sound “wet” due to pooling of secretions in the larynx and hypopharynx (▶Fig. 9.1). Dysarthria, including slurred speech, may also be present due to hypoglossal nerve palsy unless the patient has compensated for it already.
9.2.3 Examination
A complete head and neck examination is performed on every patient. Special attention should be given to any mass or lesion found that is suspicious for a neoplasm.
A complete cranial nerve examination is to be done with special attention paid to cranial nerves IX, X, and XII. The glossopharyngeal nerve plays an important role in the pharyngeal phase of swallowing. Glossopharyngeal nerve palsy is best demonstrated with asking the patient to say “ahh” and observing for palate rise. Also, the gag reflex can be tested by touching the palate with a tongue blade. The patient with CN IX palsy will display a decrease gag reflex due to decreased palatal sensation and decreased palatal elevation. Decreased contact of the palate to posterior pharyngeal wall can lead to an incomplete velopharyngeal seal, which leads to nasal regurgitation of foods. The patient can also present with poor pharyngeal constrictor muscle contraction. This can be assessed on flexible fiberoptic laryngoscopy (FFL) in which a small flexible endoscope is passed through the nose and used to view the throat from above. The patient is instructed to carry out a forceful “eee” while watching the pharyngeal walls for contraction (pharyngeal squeeze). This can be graded as normal or abnormal, and when poorly functioning, it can indicate an aspiration risk.
The hypoglossal nerve innervates the tongue muscles and therefore plays a vital role in the oral preparatory and oral phases of swallowing where it facilitates formation of and movement of the bolus. The hypoglossal nerve is examined by asking the patient to protrude his or her tongue and move it side to side. Patients with CN XII palsy will have deviation of the tongue to the weak side as well as muscle wasting and fasciculations. One can also ask the patient to push their tongue against their cheek to check strength.
The vagus nerve plays an important role in the pharyngeal phase of swallowing, of which glottic closure is the hallmark. Vagal lesions above the nodose ganglion result in deficits of both the recurrent and superior laryngeal nerves, which leads to unilateral vocal fold paralysis and decreased sensation to the supraglottic larynx, respectively. This may lead to “silent” aspiration in which aspiration occurs asymptomatically due to loss of cough reflex. Loss of the vagal contribution to the pharyngeal plexus may also cause incoordination of the pharyngeal constrictors and incomplete relaxation of the cricopharyngeus muscle during swallowing. Similar to CN IX injury with subsequent pharyngeal plexus injury, patients with CN X injury will show decreased gag reflex and the uvula may be deviated to the side of the lesion. The voice is assessed for breathiness, pitch, and projection.
The larynx is best evaluated using FFL ($115), which can be performed in the office or at the bedside. It should be part of every dysphagia and dysphonia workup done by an otolaryngologist. When testing laryngeal movement and sensation, an anesthetizing agent should not be sprayed through the nostril as this could show a false-positive loss of sensation; the agent should be placed on a pledget and placed in the nasal cavity only in order to prevent anesthetizing the pharynx and larynx.
Injury to the recurrent laryngeal nerve typically presents with voice complaints and a paralyzed vocal cord being visualized in the paramedian position leading to an incomplete glottic closure. Over time, this can lead to atrophy, which will cause bowing and flaccidity of the vocal fold. The fold will typically be shortened with anterior displacement of the arytenoid. Many can accommodate to this deficit, but when there is also a loss of sensation as in a high vagal injury mentioned earlier, this often leads to significant aspiration.
The tip of the scope should be used to test laryngeal sensation. If the patient is insensate when touching the pharyngeal wall and supraglottis, it suggests superior laryngeal nerve involvement. Pooling of secretions in the ipsilateral pyriform sinus and post cricoid areas can be seen, indicating pharyngeal weakness. If severe, this can result in a suboptimal laryngeal examination. Frank “silent” aspiration of saliva can also be detected when it is freely aspirated into the tracheobronchial tree. Again, pharyngeal squeeze is useful in assessing pharyngeal muscular contraction and when absent signifies a higher risk of aspiration.
9.3 Differential Diagnosis
Lesions/palsies of lower cranial nerves have many causes: genetic, vascular, traumatic, iatrogenic, infectious, immunologic, metabolic, nutritional, degenerative, or neoplastic. Some of the causes include motor neuron disorders, amyotrophic lateral sclerosis (ALS), ischemic stroke, aneurysm, vasculitis, skull base fracture, carotid surgery and neck dissection, varicella zoster, Guillain–Barré syndrome, multiple sclerosis (MS), diabetes, vitamin B deficiency, and skull base neoplasms such as paraganglioma tumors (▶Fig. 9.2). The work up described in the following section will be helpful in determining the exact cause and subsequent treatment.
9.4 Workup
9.4.1 Imaging
Imaging is essential in the evaluation of dysphagia. The first test is a modified barium swallow study (MBSS), which is a “live” fluoroscopic view of bolus passing through the throat (see the following text) to determine the degree of dysphagia/aspiration and where the abnormality lies. Both CT and MR imaging of the skull base and neck may be used to assess for intracranial, skull base, or neck pathology.
9.4.2 Modified Barium Swallow Study
If an MBSS has not been previously done by the referring physician, one must be ordered as the initial test. MBSS is the gold standard for diagnosing and treating dysphagia (▶Fig. 9.3). A speech pathologist and a radiologist perform this test jointly in the radiology suite. This is a dynamic study that tests three consistencies of food: thin (liquid), thick (puree), and solid foods. All phases of swallowing are evaluated. Each phase of swallowing is closely analyzed and therapeutic maneuvers are taught to the patient during the test and their effectiveness is determined. A diet is then recommended to the patient and dysphagia exercises are taught. If the patient aspirates all consistencies, particularly if silent aspiration is present, a percutaneous gastrostomy or jejunostomy tube is recommended for nutrition while the patient is undergoing rehabilitation or surgical treatment for dysphagia. The disadvantages of the MBSS include the need to travel to the radiology suite, the need for specialized personnel, and its inability to always provide information about the subtle abnormalities of the palate, vocal folds, pharyngeal musculature, and sensation.
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