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Flexible Laryngoscopy

Yolanda D. Heman-Ackah

Flexible laryngoscopy is performed to gain a dynamic assessment of the larynx during phonation. It can serve as a useful adjunct to rigid and indirect laryngoscopy; as indirect methods of evaluating the larynx usually require protrusion of the tongue to facilitate adequate visualization of the larynx.^1,2 Flexible laryngoscopy, on the other hand, allows the examiner to evaluate the larynx in its normal anatomic position during various phonatory maneuvers and to gain a better understanding of the patient’s vocal habits and vocal posturing during vocalization. Such an understanding can help with accurate diagnosis and in developing a treatment plan that addresses all aspects of the vocal mechanism contributing to voice complaints and vocal pathologies.

Choice of Instrumentation

There are numerous options in instrumentation available currently for flexible laryngoscopy. These include systems that use a distal “chip-tip” camera versus a traditional camera positioned at the eyepiece of the laryngoscope. The chip-tip camera is a small camera positioned at the tip of the flexible laryngoscope. The advantage of the chip-tip laryngoscope is that the distal placement of the camera allows a more magnified view of the larynx with better resolution than can be achieved with the placement of the camera at the eyepiece of the laryngoscope.^1,3–5 The light source chosen to be used with the flexible laryngoscope can be either a continuous halogen light or a stroboscopic light. Halogen light sources are often used for dynamic assessment of the supraglottic and glottic vocal tract during phonation and for anatomic evaluation of the larynx and its component structures. Stroboscopic light allows for the evaluation of the vibratory function of the vocal folds via flashing lights. The magnification and resolution achieved with currently available chip-tip flexible laryngoscopes for stroboscopic evaluation of the larynx is good, but more detail is usually appreciated with the greater magnification available with rigid endoscopes.^6,7 When portability is of benefit, flexible laryngoscopes with battery-operated light sources can be beneficial. In all cases, the ability to record the examination is invaluable not only in patient education but also in allowing the clinician the ability to take a sufficient amount of time to review subtle abnormalities of the larynx in great detail without the patient discomfort that often accompanies such attention in the absence of a video recording. Additionally, the ability to compare examinations over the course of time is a benefit of maintaining a video record.

The most valuable use of the flexible laryngoscope is in the evaluation of movement disorders of the larynx and in evaluation of supraglottic function during phonation.2,8–10

Anesthesia

The flexible laryngoscopic examination can be performed with or without topical anesthesia, and there are certain situations when either is appropriate.¹¹ Topical anesthesia in the larynx allows the clinician to position the laryngoscope within the laryngeal inlet, within several millimeters of the vocal folds without causing much patient discomfort, coughing, or choking. This can be particularly beneficial in patients with a significant amount of tongue base tension, in whom an adequate assessment of vocal fold mobility cannot be performed easily with the telescope positioned at or above the level of the tongue base. The use of topical anesthetics is also beneficial when stroboscopic evaluation of the larynx is performed with the flexible laryngoscope, as it allows a closer, more magnified view of lesions on the vocal fold and greater resolution for evaluation of the mucosal wave. When sensory deficits are suspected, the use of topical anesthetics can interfere with the ability to perform sensory testing, which usually is performed through a flexible laryngoscope that is designed to deliver calibrated puffs of air through an operating channel to laryngeal mucosa. However, in the absence of a need for sensory testing, topical anesthesia is usually recommended. Many clinicians use a nasal decongestant such as oxymetazoline hydrochloride or phenylephrine combined with a topical anesthetic in the nose such as Pontocaine (tetracaine) and a topical anesthetic in the mouth and laryngeal inlet such as Cetacaine. Because there is a slight risk of methemoglobinemia with use of local anesthetics, care must be taken not to use too much anesthetic and not to use anesthetic at all in those who are at risk of developing it.

Technique of Flexible Laryngoscopy

Positioning of the patient for flexible laryngoscopy is key for optimal examination results.¹² Ideally, the patient should be seated, with the head in the neutral position, eyes open, and face relaxed. A relaxed face allows for ease of passage of the laryngoscope into the nose. A small amount of lubricant on the tip of the scope will facilitate passage of the telescope through the nose with minimal patient discomfort, especially when sufficient amount of time has been allowed for nasal decongestion after application of oxymetazoline or phenylephrine. The scope should be passed along the floor of the nose, into the nasopharynx and then turned inferiorly for a view of the hypopharynx and, in particular, the larynx. Closure of the eyes during the examination results in posturing of the larynx that can easily be confused with supraglottic hyperfunction. For this reason, patients should be encouraged to keep their eyes open at all times during the examination. It can be extremely helpful to have a video monitor positioned behind the examiner for the patient to view during the examination. This provides excellent feedback to the patient and helps to reduce anxiety that can sometimes be provoked by the presence of the laryngoscope in the nose.

The flexible laryngoscope is passed through the nose, either beneath the inferior turbinate or between the inferior and middle turbinates in the nose. Care must be taken not to let the tip of the laryngoscope touch the turbinates or septum, as this will result in significant patient discomfort and/or pain. Once the laryngoscope reaches the back of the nose, it is flexed downwards, and the patient is instructed to breathe through the nose. In doing so, the patient will relax the soft palate, opening the posterior nasopharynx wide enough to allow the passage of the laryngoscope into the oropharynx and from there into the hypopharynx and laryngeal inlet.

At this point in the examination, it is best to use halogen light. It allows for evaluation of all of the anatomic structures of the upper aerodigestive tract, without distortion or shadows that can sometimes obscure the anatomy when stroboscopic light is used. A full evaluation of the nasal cavity, nasopharynx, eustachian tubes, soft palate, tonsils, base of tongue, vallecula, piriform sinuses, posterior oropharyngeal wall, posterior hypopharyngeal wall, and larynx should be performed during this portion of the examination. The telescope can be rotated from right to left in the back of the nasopharynx to visualize the eustachian tubes. Once in the hypopharynx, protrusion of the tongue will allow evaluation of the vallecula. Having the patient puff his or her cheeks with closed lips will distend the piriform sinuses. Evaluation of each of these structures for inflammatory, infectious, and neoplastic lesions should always be a routine component of the voice evaluation.

Once an anatomic survey has been completed, the examination can proceed to evaluation of vocal function. The first step in the examination is evaluation of quiet breathing. During normal respiration, the vocal folds should slightly abduct during inspiration and slightly adduct during expiration. When these movements are reversed, paradoxical vocal fold motions are said to exist. Such paradoxical movements can signify laryngeal hyperexcitability that could contribute to laryngeal spasms in response to environmental stimuli such as reflux or allergy. Other than these slight movements of the vocal folds with respiration, there should be no other spontaneous movements in the larynx during quiet breathing. The presence of involuntary, irregular, arrhythmic, jerky movements of the larynx implies laryngeal myoclonus. Rhythmic, involuntary twitches of the laryngeal muscles at rest imply a resting tremor. When similar involuntary, rhythmic twitches occur during phonation only, they are termed laryngeal intention tremors.13

After assessment of quiet breathing, an evaluation of the speaking voice is performed. Usually, the patient is asked to recite a familiar fact, such as his or her name and the date, to evaluate for evidence of supraglottic hyperfunction during speech. Ideally, the tongue base should be positioned anteriorly, away from the supraglottis; the vocal folds should meet in the midline with phonation, and the supraglottic muscles should be relaxed during phonation. With increased tongue base tension, the tongue will fall posteriorly and press against the epiglottis, narrowing the supraglottic inlet. When the false vocal folds and pharyngeal constrictors are overly recruited during phonation, there is squeezing of the false vocal fold mucosa in an anterior-posterior or lateral direction. In severe cases, the supraglottic mucosa may be squeezed circumferentially. Dysphonia plica ventricularis occurs when such squeezing results in approximation of the false vocal folds during phonation, so that the “voice” produced is a product of the false vocal folds vibrating against one another, rather than the true vocal folds doing so. Having the patient count from 1 to 10 helps to see whether any supraglottic hyperfunction observed during speech dissipates when the patient is performing a rote task or whether it remains the same. Hyperfunction that is present during thoughtful tasks and that disappears during a mundane task can signal task-specific hyperfunctional behavior. Having the patient raise the pitch of his or her voice to a Minnie Mouse-sounding caricature voice while counting to 10 should result in alleviation of much of the hyperfunction that is seen during normal counting. The inability to raise the pitch of the voice during this task may imply dysfunction of the superior laryngeal nerves. Strain in the voice that is present throughout speech implies supraglottic hyperfunction, which is also commonly referred to as muscle tension dysphonia. Strain that appears intermittently during speech can imply involuntary laryngeal spasms, such as can occur with reflux-induced laryngospasm, spasmodic dysphonia (also termed laryngeal dystonia), laryngeal myoclonus, laryngeal tremor, and some psychogenic laryngeal disorders.^9,12,13

Occasionally, reflux-induced laryngospasm episodes are easily apparent during the examination. The examiner will see reflux material come up from the cricopharyngeal region and trickle onto the arytenoids and into the laryngeal inlet. At the moment that the refluxate touches the arytenoids or vocal folds, they will spasm, and a concomitant break in speech, characterized by sudden strain, is observed.

Spasmodic dysphonia is a focal dystonia of the larynx that can involve either the intrinsic adductor or abductor muscles of the larynx or both sets of muscles. Adductor spasmodic dysphonia is characterized by involuntary spasms of the adductor muscles of the larynx. These spasms tend to occur during voiced sounds of speech. The best way to elicit adductor spasms is to have the patient count from 80 to 89. Usually, the /ay/ sound in “eighty” will cause an adductor spasm, and that sound will sound strained. This spasm will then make it difficult for the patient to produce the unvoiced sound of /ti/ that follows in the word eighty. Abductor spasmodic dysphonia is characterized by involuntary spasms of the abductor muscles in the larynx, and these tend to occur during unvoiced sounds of speech. It is easiest to elicit abductor spasms by having the patient count from 60 to 69. The sound /s/ that begins the word sixty is unvoiced and will cause an abductor spasm, making the rest of the word that follows sound breathy. Mixed spasmodic dysphonia is characterized by both adductor and abductor spasms. In all forms of spasmodic dysphonia, the spasms usually improve when the patient is asked to perform a phonatory task using a voice that is different from his or her usual and habitual communicative voice. Such tasks may include talking in a caricature voice like that of “Minnie Mouse” or singing.^9,12,13

The next phonatory task specifically looks at superior laryngeal nerve function. It involves having the patient perform the glissando maneuver on the vowel /i/. In this task, the patient slides from the lowest pitch he or she can access to the highest pitch in his or her vocal range while phonating the vowel /i/, then sliding down from high to low. Ideally, both vocal folds should show a progressive and smooth increase in longitudinal tension (ie, the length of the vocal fold from the arytenoid to the anterior commissure should increase as pitch increases) as the patient goes from low to high and a reversal of this motion as he or she goes from high to low. The examiner is not only noting whether or not the vocal folds lengthen with voluntary increase in pitch but is also noting whether or not the lengthening of the vocal folds is symmetric and whether or not there is a tilting of the larynx as the pitch is increased. Asymmetric lengthening of the vocal folds with voluntary increase in pitch implies a relative weakness or paresis of the superior laryngeal nerve/ cricothyroid muscle on the side that is foreshortened. Similarly, tilting of the larynx during voluntary increase in pitch implies a superior laryngeal nerve paresis on the side toward which the larynx tilts as the pitch is raised.2,8–10,12–14

The function of the abductor muscles of the larynx is evaluated by having the patient perform serial abductory laryngeal tasks. Having the patient sniff through the nose forcefully and quickly at least five times in rapid succession will assess the isolated function of the posterior cricoarytenoid muscles, the laryngeal abductors. Ideally, the vocal folds should abduct symmetrically during the sniffs. When assessing the degree of symmetry, the examiner is paying close attention to the extent to which the vocal folds open from the midline on each side, whether or not that excursion is the same or if one vocal fold appears to open slightly wider than does the other, and whether or not the quickness with which the vocal folds move is symmetric or if one vocal fold tends to move slightly more briskly than the other. Asymmetries in lateral excursion of the vocal folds or in the briskness of abduction of the vocal folds may imply dysfunction of the involved posterior cricoarytenoid muscle or the branch of the recurrent laryngeal nerve that innervates that muscle.

Having the patient whistle a tune, such as “Yankee Doodle,” allows the examiner to evaluate the adductor and abductor functions of the larynx while at the same time eliminating the supraglottic hyperfunction that can accompany speech and that can obscure subtle abnormalities in vocal fold mobility. A tune with a quick beat will cause rapid adduction and abduction of the vocal folds, which is beneficial in assessing the rapidity of vocal fold motion. Attention is focused on symmetry of motion of the vocal folds, symmetry of both lateral and medial excursion of the vocal folds, and symmetry in briskness in movement of the vocal folds. Asymmetries in adduction may imply paresis or dysfunction in any of the adductory muscles of the larynx, including the thyroarytenoid, lateral cricoarytenoid, the interarytenoid, or the cricothyroid muscles. Asymmetries in abduction imply paresis or dysfunction of the posterior cricoarytenoid muscle. Asymmetries in adduction can also be elicited by having the patient alternate rapidly between the sounds /i/-/hi/-/i/-/hi/-/i/-/hi….2,8–10,12–14

The ability to coordinate the actions of the opposing muscle groups in the larynx is assessed by having the patient repetitively and quickly alternate between strong adductory and abductory movements. The task of repeatedly alternating between a forceful sniff and the sound /i/ is one of the best tasks for assessing coordination in the larynx. The inability to rapidly alternate between abduction and adduction implies laryngeal dysdiadokinesis. Any systemic neurologic disorder that can cause dysdiadokinesis in other muscle groups can also cause dysdiadokinesis in the larynx. These typically are signs of an extrapyramidal cause.¹³ One of the most common causes in the larynx is laryngeal dystonia (spasmodic dysphonia). Parkinsonism is another. Laryngeal cogwheeling, seen as jerky movements of the adductor muscles as they attempt to go from the open position of the sniff to the closed position of the /i/, can also be elicited in this maneuver. Cogwheeling is a sign of laryngeal rigidity and can be seen in upper motor neuron disorders that cause spasticity as well as in Parkinsonism.^13,14

Dysdiadokinesia can also be elicited by having the patient repeatedly say the sounds /pa/-/ta/-/ka/-/pa/-/ta/-/ka/-/pa/-/ta/-/ka/-/pa/-/ta/-/ka/-/pa/-/ta/-/ka/…. This task involves more rapid movement of the adductors and abductors and will elicit subtle abnormalities in coordination that may not be readily apparent in alternating between a sniff and the sound /i/. Additionally, the task /pa/-/ta/-/ka/-/pa/-/ta/-/ka/-/pa/-/ta/-/ka/-/pa/-/ta/-/ka/-/pa/-/ta/-/ka/… allows one to evaluate for rapidity of movement. The inability to say these sounds rapidly in succession implies laryngeal bradykinesia, which is often seen in basal ganglia disorders such as laryngeal dystonias and Parkinsonism.¹³

Whether or not the patient is a singer, it is always important to evaluate the singing voice as well as the speaking voice.^9,10,12 Usually, it is best to have the patient sing a tune with which he or she is very familiar, such as “Happy Birthday,” or another similar tune in their native language if English is the second language. For instance, “La Cucaracha” is a song that most Spanish-speaking patients will know, and this can be used to evaluate the singing voice in this situation. Familiarity with a song that is commonly sung usually eliminates the desire for the patient to “perform” and allows for assessment of hyperfunction, breathing patterns, and vocal fold mobility during a task that the patient does not associate with normal speech. This can be particularly helpful again in patients with psychogenic voice disorders, as it is harder for the patient to manipulate the voice throughout the vocal range. During singing, inconsistencies in vocal fold mobility and longitudinal tension can be elicited that may be more difficult to ascertain during other phonatory maneuvers. Patients with spasmodic dysphonia will typically have a completely normal singing voice, regardless of the degree of severity of the dysphonia in the speaking voice. In patients who are singers, it is important to also have them sing a song or two from their normal repertoire to evaluate how they use their vocal mechanism during vocal performance. Oftentimes, laryngeal postures and habits are different during singing in professional and avocational singers than they are during speech, and it is important to make this distinction.

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