CHAPTER 59 Neurologic Evaluation of the Larynx and Pharynx
The upper aerodigestive tract serves the diverse purposes of breathing, eating, and communicating. These activities require some orthogonal functions. For example, pharyngeal patency should be maintained during respiration, but the pharynx should be forcibly constricted during swallowing. In addition, the anatomic structure of the upper aerodigestive tract is precarious, with ingested food and inspired air traversing the same space. Precise coordination of motor activity and appropriate response to sensory feedback are essential for normal function. Neurologic disorders may impair upper aerodigestive tract function by diverse mechanisms, including motor weakness, incoordination, and impairment of sensation.1,2
The diagnosis of disorders in patients with neurologically impaired function of the upper aerodigestive tract is often elusive, particularly when the problem is isolated to that region. The reason is that the ability of the throat and larynx to function cannot be directly observed. Patients with complaints of hoarseness, dysarthria, dysphagia, aspiration, or airway obstruction are often seen by otolaryngologists, whose training emphasized morphologic rather than functional evaluation. Neurologists, whose forte is functional assessment, generally confine their evaluations to structures that are more accessible, such as limbs. If the anatomy is normal and if no functional deficit is noted on a traditional neurologic examination, a patient who actually has a neurologic impairment is often incorrectly assumed to have a functional or psychiatric disorder. Thus, the diagnosis of a generalized neurologic disorder, such as myasthenia gravis or amyotrophic lateral sclerosis (ALS), may be delayed until the disease process is more widespread and apparent. As a result, patients may receive well-intentioned but ineffective therapy instead of potentially effective treatment.3–5
The diagnosis of neurologic impairment of the upper airway requires an awareness of the possibility of neural dysfunction, familiarity with the signs and symptoms of neural dysfunction, and a systematic approach to the examination of the throat and pharynx. Box 59-1 lists some symptoms that suggest neurologic impairment. The patient’s interests are best served by the collaborative efforts of the otolaryngologist, who is highly skilled in visualizing the throat and larynx, and the neurologist, who is knowledgeable in the pathophysiologic processes. This chapter reviews normal physiology and salient features of specific neurologic diseases that affect function, outlines the approach to the history and physical examination of patients in whom such diseases are suspected, and discusses how ancillary tests may be useful.
Box 59-1 Laryngeal and Pharyngeal Symptoms Suggesting Neuropathology
Normal Function
Phylogenetically, the most important function of the larynx is protective; the larynx prevents ingested food and drink from entering the lungs. To fulfill this role in humans, the larynx should be open during breathing and tightly closed during swallowing. Phonation is a more advanced evolutionary function. Glottic closure during forced exhalation results in an effective cough to clean the lungs and prevent atelectasis. Laryngeal closure is required to generate positive intrathoracic pressure for defecation, childbirth, and lifting heavy objects and for the stabilization of the thorax. The larynx also seems to play a sophisticated role in controlling airflow and pressure during breathing. The vocal folds open just before respiration and then close gradually during exhalation, braking expiratory airflow and thereby influencing the rate of breathing. The sensory feedback loops that control these respiratory functions of the larynx are not well understood, but it is clear that feedback from a variety of receptors is involved.1,2,6
Swallowing is a deceptively simple function. Food prepared in the mouth is ejected into the pharynx and then rapidly propelled downward around the glottis, through the pyriform sinus, and into the esophagus. During the swallow, the same pharynx that remains patent during breathing is responsible for constricting tightly in an organized sequence from top to bottom. Regurgitation into the nose or reflux into the mouth is prevented by actions of the soft palate, tonsillar pillars, and base of the tongue. The larynx is pulled upward and forward, away from the flow of the bolus. This action also decompresses the sphincter between the pharynx and esophagus. Flexion of the epiglottis and closure of the glottis prevent the entry of any errant material into the airway. After this complex and coordinated activity, the cricopharyngeal muscle should be relaxed when the bolus reaches the caudal end of the pharynx to permit passage into the esophagus. If pharyngeal peristalsis is inadequate or if the upper esophageal sphincter is insufficiently opened, residual material in the pharynx could penetrate the airway during the next inhalation. The unique anatomic configuration in humans after infancy renders swallowing more difficult. In all other mammals, the feeding and breathing channels are offered a degree of separation by interdigitation of the epiglottis and uvula. In humans, these structures are separated during early development by the descent of the larynx relative to the palate.7–9
Speech is audible communication that results from phonation, resonance, and articulation. The production of sound (phonation) requires several conditions. Expired airflow and pressure should be sufficient to induce oscillation of the vocal folds. The vocal folds should be appropriately approximated. If they are closed tightly, excessive expiratory force is required, resulting in a strained, harsh voice or complete aphonia. If the vocal folds are too far apart, increased expiratory airflow volume is required, so that the voice becomes weaker and breathier or even fades to a whisper. The three-dimensional shape of the vocal fold is also important in imparting favorable aerodynamic features to the glottis. Atrophy of the vocal fold causes concavity in the axial and coronal planes. The former results in incomplete glottal closure even during tight approximation of the vocal processes. Concavity in the coronal plane results in a convergent airflow tract. Control of length and tension is required to produce normal inflections in pitch and tone. In the absence of such control, the voice may be flat and expressionless, or it may be distorted by uncontrolled pitch breaks. The mucosa of the vocal folds should be supple to permit free vibration. All but the last of these requirements for phonation are susceptible to derangement by neurologic dysfunction.10,11
Resonance is the modification of phonation to produce voice. Pure phonated sound as produced by the vocal folds does not sound like a human voice; it is a strident and unpleasant noise. This sound is modified by resonance of the head, neck, and chest so that component frequencies are selectively amplified or dampened. Vocal resonance is largely determined by anatomy, but it also is significantly modulated by motor activity of the pharynx, soft palate, and oral cavity. This principle may be used in speech therapy to achieve stronger voices in patients with impaired function. Certain neurologic disorders, such as ALS, stroke, and Guillain-Barré syndrome, result in altered vocal resonance. The characteristic sound of the voice in patients with these disorders may be a valuable physical sign to aid in early diagnosis.10,11
Articulation is the shaping of voice into words by actions of the lips, tongue, palate, pharynx, and larynx and is highly susceptible to neurologic impairment. Whereas dysarthria in children is caused most often by a hearing deficit, acquired dysarthria in adults usually indicates neurologic impairment. Dysarthria may be a result of impaired motor output, such as weakness, paralysis, or incoordination, but may also result from cognitive or language defects or from apraxia of speech.10,11
Neurologic Examination of the Mouth, Larynx, and Pharynx
The standard neurologic examination does not address the relatively inaccessible regions that are familiar to the otolaryngologist. The following protocol is suggested as a systematic approach to detecting neurologic dysfunction. The objectives are to assess the integrity of the lower cranial nerves and to seek signs of central nervous system disorders.10
Oral Cavity
Observe the lips, palate, and tongue for abnormal spontaneous movement. Involuntary, slow, athetoid movements of the tongue occur in patients with tardive dyskinesia, which is usually a reaction to a major tranquilizer. A quivering, “bag of worms” appearance indicates fasciculations, a characteristic sign of ALS. Spasmodic motions, in particular excessive blinking and jaw thrusting, are characteristic of Meige’s syndrome. Assess range of motion, strength, and symmetry of the mouth and palate muscles as usual. Ask the patient to purse the lips, to protrude the tongue and move it from side to side, and to open the mouth and say the traditional /ah/ to test for palate motion and symmetry. The best way to assess tongue strength is to have the patient push the tongue against the buccal mucosa while the physician palpates the cheek externally.10
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
