Neurolaryngologic Evaluation of the Performer




Numerous neurologic diseases affect voice production either through direct effects on the larynx or by affecting muscles involved with support or resonation of the voice. Voice changes can be the initial presenting symptoms of neurodegenerative disorders, especially in patients who have increased awareness of their vocal quality. Some patients present to the otolaryngologist before the neurologist. The otolaryngologist must have an understanding and familiarity with laryngeal manifestations of neurodegenerative diseases to make the appropriate diagnosis in a timely fashion. Moreover, the otolaryngologist can play a significant role in the care of patients who have neurodegenerative disease. Video procedures for neurolaryngologic evaluation accompany this content online.


Innervation of voice and speech


The neuroanatomy of voice and speech is complex. An intricate neural network is responsible for ensuring that the larynx performs its main functions: providing and protecting the airway, producing cough and Valsalva, and producing voice. The complexity is greater considering all of the other muscles of support and articulation that need to be coordinated during voice and speech production. Human beings have more voluntary control over the laryngeal and articulating muscles than other animal species. Although more primitive visceromotor pathways are involved, particularly with more cathartic vocal functions, human voice production is marked by greater cortical control . As with other voluntary motor systems, the neuromuscular pathway of voice and speech production involves upper and lower motor neurons, the basal ganglia and cerebellum, neuromuscular junctions, and the target muscle.


Central innervation


Upper motor neurons relay signals from the cortex to lower motor neurons in the brainstem and spinal cord to initiate voluntary movement . Numerous cortical areas contribute to vocalization. Some areas are excitatory, whereas others are inhibitory. Cortical input affecting vocal fold movement is bilateral, which is why a unilateral cortical injury seldom results in a complete vocal fold paralysis. There is hemispheric specialization with speech production, however, with the left primary motor cortex playing a more dominant role . The right motor cortex likely plays an important role in the prosody, or melody, of speech .


The cell bodies of the laryngeal nerves lie within the nucleus ambiguus in the medulla. In addition to upper motor neuron input, these lower motor neurons receive input from other brainstem nuclei, including the nucleus tractus solitarius and nucleus parabrachialis. This complex network of interconnections integrates afferent input and modifies reflexes. Other synapses occur from neurons in the periaqueductal gray matter, the final pathway of the visceromotor system, and are likely involved in the cathartic functions of voice, such as during crying or screaming . The lower motor neuron is the final common pathway to the target muscle .


Extrapyramidal system


Upper and lower motor neurons are part of the pyramidal system and control voluntary movement. The basal ganglia and cerebellum are part of the extrapyramidal system. The extrapyramidal system is important in controlling gross motor function. It inhibits erratic movements and helps maintain muscle tone. The basal ganglia inhibit the rapid firing of motor neurons (the “release phenomenon”). They receive input from most cortical areas and send output to areas of the frontal cortex involved with planning movement. The cerebellum improves accuracy of movement by comparing central motor commands with sensory input from the periphery . It is likely involved in vocal self-monitoring and fine-tune adjustments in pitch and airflow . Neurodegenerative processes involving the extrapyramidal system may result in abnormal movement, such as tremor, dystonia, dysdiadokinesia, as well as, abnormal muscle tone .


Peripheral innervation


The motor nerves (cranial and spinal) synapse at the motor endplate of the target muscle. This synapse is called the neuromuscular junction. The neurotransmitter acetylcholine is released from the nerve terminal and triggers an action potential, which results in muscle contraction.


The intrinsic muscles of the larynx are supplied by the recurrent (RLN) and superior (SLN) laryngeal nerves. The nerve fibers travel within the vagus nerve through the jugular foramen of the skull base. The RLN branches from the vagus within the superior mediastinum and loops around the aortic arch on the left and subclavian artery on the right. It travels back superiorly within or just lateral to the tracheoesophageal groove until it enters the larynx posterior to the cricothyroid joint. The SLN branches off the vagus nerve just inferior to the nodose ganglion. The nodose ganglion contains the sensory cell bodies of the SLN. The SLN travels inferiorly along the side of the pharynx, medial to the carotid artery, and splits into two branches at about the level of the hyoid bone. The internal division of the SLN penetrates the thyrohyoid membrane with the superior laryngeal artery and supplies sensory innervation to the larynx. The external division of the SLN provides motor innervation to the cricothyroid (CT) muscle.


The RLN innervates all of the intrinsic muscles of the larynx except the cricothyroid. These include the thyroarytenoid (TA), posterior cricoarytenoid (PCA), lateral cricoarytenoid (LCA), and interarytenoid (IA) muscles. Muscle innervation is unilateral except for the IA muscle, which receives contributions from both RLNs . The TA and LCA muscles are vocal fold adductors. Unilateral denervation of these muscles results in an inability to close the glottis, with resulting breathy voice and possible aspiration .


The PCA is the main vocal fold abductor. Paralysis of this muscle results in an inability to abduct during inspiration. When both PCA muscles are denervated, airway obstruction may occur. Denervation of the PCA may cause the arytenoid cartilage to subluxate anteromedially in unilateral vocal fold paralysis. The denervated PCA no longer counters the anterior pull on the arytenoid cartilage by the vocal ligament .


The SLN branches from the vagus nerve just inferior to the nodose ganglion, which contains the sensory cell bodies of the SLN. The SLN branches into an internal and external division. The internal division of the SLN penetrates the thyrohyoid membrane with the superior laryngeal artery and supplies sensory innervation to the larynx. The external division of the SLN provides motor innervation to the cricothyroid (CT) muscle. Unopposed CT muscle contraction lengthens the vocal fold, increasing tension and thus the fundamental frequency of the voice .


Although the intrinsic laryngeal muscles are classically described as abductors and adductors, their functions are more complex. Antagonistic muscles contract simultaneously during normal vocal function. For example, unopposed TA contraction results in shortening of the vocal fold. It acts synergistically with the CT muscle to affect vocal fold tension . CT muscle function may also depend on the position of the vocal fold at the time of contraction. It may be active with some voice production regardless of pitch variation. Different patterns of intrinsic muscle activation are seen depending on the purpose of motion. For example, different muscles may be activated or deactivated during adduction or abduction depending on whether the motion occurs during cough, respiration, or voice production. The CT muscle is active during abduction with sniff, but not respiration .




Manifestations of neurologic disease


Neurologic disorders may affect voice and speech production in several ways. Central injury may affect initiation, coordination, and quality of voice and speech. Direct effects on the larynx can affect glottic closure patterns and efficiency along with laryngeal muscle tone. Denervation of muscles involved in the support mechanism of the voice, such as the diaphragm or chest wall musculature, affects voice strength and quality. Dysfunction of oropharyngeal musculature may affect resonance. A palatal paralysis results in a more hypernasal voice. Impairment of cranial nerve V, VII, or XII function can affect articulation. Findings on general neurologic and laryngeal examination depend on which nerves are involved and where the disorder affects the neuromuscular pathway ( Table 1 ).



Table 1

Laryngeal and general findings of neurologic disease




























Site of lesion General findings Laryngeal/speech findings
Upper motor neuron Spasticity, hyperreflexia, rigidity, positive Babinski sign, myoclonus Spastic vocal fold paralysis/paresis, spastic dysarthria, laryngeal myoclonus
Lower motor neuron Weakness, flaccidity, fasciculations Flaccid vocal fold paralysis/paresis, glottic insufficiency, hypernasal speech, flaccid dysarthria
Extrapyramidal Tremor (pill-rolling in Parkinson’s disease), dystonia, dyskinesia, dysdiadochokinesia Vocal fold bowing, mid-fold insufficiency, tremor, laryngeal dystonia, dysdiadochokinesia
Peripheral nerve Weakness, atrophy, sensory deficits Hypomobility, immobility, ?atrophy (tone depends on degree of reinnervation)
Myopathy Weakness, flaccidity Hypomobility, flaccidity


Motor neuron diseases


Motor neuron diseases may result from degeneration of upper motor neurons, lower motor neurons, or both. When both upper and lower motor neurons are involved, the diagnosis of amyotrophic lateral sclerosis (ALS) or Lou Gherig’s Disease is made . ALS is fatal, usually from respiratory failure, but the clinical course is variable. Other examples of upper motor neuron disease processes include progressive lateral sclerosis and pseudobulbar palsy. Primary lateral sclerosis typically involves destruction of upper motor neurons only. The diagnosis is typically made after 4 years of predominantly upper motor neuron involvement . Pseudobulbar palsy results from interruption of bilateral corticospinal tract axons from other disease processes, such as stroke, multiple sclerosis, or tumor, as opposed to destruction of the neuronal cell body itself . Patients who have pseudobulbar palsy often have inappropriate emotional outbursts. A pseudobulbar palsy affect is often seen in patients who have ALS .


Lower motor neuron diseases include ALS, progressive bulbar palsy, and spinal muscle atrophy. Progressive bulbar palsy is essentially ALS affecting only the cranial nerves. Progressive spinal atrophy includes several autosomal-recessive disorders that involve degeneration of the anterior horn cells of the spinal cord. Although some forms present in adulthood, many present in younger patients .


Physical findings differ between upper and lower motor neuron processes. Upper motor neuron findings include spasticity of musculature and hyperreflexia. Spasticity of laryngeal musculature often results in a strained voice that might be misconstrued as spasmodic dysphonia. Patients may suffer from intermittent laryngospasm. Spasticity of oral musculature results in strained, effortful dysarthria. Myoclonus may occur. Extremity involvement may be noted. A positive Babinski reflex is a classic finding of upper motor neuron disease .


Lower motor neuron processes result in flaccid paralysis, muscle atrophy, and fasciculations. Patients may develop weak, breathy voices, bowing of the vocal folds, and poor cough. Palatal involvement may lead to nasal regurgitation and hypernasal speech. Pharyngeal musculature involvement leads to oropharyngeal dysphagia. Tongue and facial muscle involvement leads to slurred speech and oral dysphagia. With poor oral motor function, pharyngeal squeeze, and glottic incompetence, these patients are often at significant risk for aspiration .


Cerebrovascular accident


Cerebrovascular accidents may present with upper and lower motor neuron findings depending on the size and location of the stroke. Strokes may result from ischemia (secondary to thrombosis or hypotension) or hemorrhage. Unilateral cortical strokes are unlikely to result in complete vocal fold paralysis because of bilateral cerebral innervation of the laryngeal nerves. Brainstem stroke may cause vocal fold paralysis if disruption of the nucleus ambiguus or corticobulbar fibers synapsing with the nucleus ambiguus occurs. Isolated vocal fold paralysis secondary to stroke is rare. Wallenberg syndrome or lateral medullary syndrome results from occlusion of the posterior inferior cerebellar artery. It may result in some combination of vocal fold paresis or paralysis, decrease in ipsilateral facial pain and temperature, decrease in contralateral body pain and temperature, dysphagia, dysarthria, vertigo, Horner syndrome, ataxia, and hiccoughs . Stroke patients often are debilitated, which also contributes to poor voice quality. Abnormal body positioning and strength contribute to vocal problems. In addition, these patients often have significant dysphagia and are at high risk for aspiration pneumonia.


Extrapyramidal diseases


Diseases of the extrapyramidal system include Parkinson’s disease, spasmodic dysphonia, and laryngeal tremor. Parkinson’s disease is a movement disorder resulting from degeneration of dopamine-secreting cells within the substantia nigra of the brainstem. This process results in loss of the neural pathways through the basal ganglia that are involved in control of movement. Classic findings include tremor, rigidity, bradykinesia, and postural instability.


(Access Video on Parkinsonian Cogwheeling in online version of this article at: http://www.oto.theclinics.com/ .)


More than 70% of patients who have Parkinson’s disease have voice and speech manifestations. Patients who have Parkinson’s disease often have soft, breathy, monotonal voices. Laryngeal tremor is common. Patients often perceive their voice as normal. Affect is often flat (“masked”). In addition, patients who have Parkinson’s disease may have significant dysarthria and dysphagia. Characteristic laryngeal signs include vocal fold bowing, glottic insufficiency, and slow vibration. The glottic insufficiency and poor breath support attributable to debilitation and chest wall rigidity result in a soft, breathy voice quality .


Vocal fold paralysis should raise suspicion of a Parkinson plus syndrome, such as progressive supranuclear palsy, Shy-Drager syndrome, and multisystem atrophy. These disease processes are usually more rapidly progressing and less responsive to medication. In addition, patients who have multisystem atrophy are at risk for bilateral vocal fold paralysis and airway obstruction .


Spasmodic dysphonia


Spasmodic dysphonia (SD) is a focal dystonia the larynx. As with other dystonias, it is characterized by involuntary muscle contractions or spasms. These spasms are task-specific. Adductory spasmodic dysphonia (AdSD) accounts for 80% of the cases of SD, with abductory (AbSD) and mixed dysphonias occurring less frequently. Patients who have AdSD have a characteristic strained/pressed quality to their voices.


(Access Video on Adductor Spasms in online version of this article at: http://www.oto.theclinics.com/ .)


They suffer voice breaks with voiced consonants. Patients who have AbSD have spasms of the PCA muscle with voiceless consonants, resulting in intermittent breathiness .


(Access Video on Mixed adductor/abductor Spasms in online version of this article at: http://www.oto.theclinics.com/ .)


The pathophysiology of SD is uncertain. It may be attributable to dysfunction of the laryngeal feedback systems resulting in disinhibition of laryngeal muscle action . Laryngeal tremor may be present in addition to the dystonia. The combination of tremor and dystonia is referred to as dystonic tremor. These entities can be difficult to distinguish at times . Spasmodic dysphonia might also be difficult to distinguish from muscle tension dysphonia or other functional dysphonias.


Laryngeal tremor


Vocal tremor presents as nearly regular oscillations of the laryngeal and pharyngeal musculature.


(Access Video on Laryngeal Tremor in online version of this article at: http://www.oto.theclinics.com/ .)


The voice is unstable with frequent breaks. Tremor may be seen as a manifestation of several neurologic diseases, including Parkinson’s, ALS, and cerebellar diseases . Usually other neurologic signs and symptoms are present when a more severe neurologic disease is present. Tremor may also be seen with and is often difficult to distinguish from spasmodic dysphonia . When laryngeal tremor is present, a thorough neurologic evaluation is required, with assessment of cranial nerve, extremity, and cerebellar function and gait.


When no other signs or symptoms are present, vocal tremor is usually a manifestation of essential tremor, one of the most common causes of voice tremor. It may be the only manifestation, but typically the extremities are involved also. The voice is affected in approximately 20% of cases of essential tremor . In addition to the intrinsic laryngeal muscles, the extrinsic laryngeal muscles, pharyngeal muscles, and muscles of respiration may be involved. The pathophysiology of tremor is incompletely understood. Electromyograph studies have demonstrated that various laryngeal muscles may oscillate at different frequencies, suggesting multiple foci of central stimulus, or peripheral contribution to the oscillatory pattern by a reflex arc. In addition, there may be different degrees of severity amongst each of the laryngeal muscles .


Myoclonus


Segmental myoclonus may occur within the pharynx and larynx. Typically, involuntary, arrhythmic, jerk-like movements are seen. Usually it is bilateral, although it may occur unilaterally. Palatopharyngeal myoclonus may produce slow, regular voice arrests that may be missed in running speech. It may also be triggered by speech and result in more rapid, dramatic voice arrests . Myoclonus is believed most commonly to arise from dysfunction or lesions within the dentate, red, and inferior olivary nuclei. Unlike tremor, it typically does not involve opposing muscle groups. Myoclonus may be seen in neurodegenerative diseases .


Neuromuscular junction


Myasthenia gravis is an autoimmune disease characterized by muscle weakness exacerbated by repetitive use and improved with rest. Antibodies are produced to the postsynaptic acetylcholine receptor at the neuromuscular junction. Although ocular involvement is most common, laryngeal myasthenia may present independently or in conjunction with other muscles .


Laryngeal finding are best appreciated with fiberoptic laryngeal examinations. Vocal fold fatigability with repetitive phonatory tasks is characteristic. Fluctuating movement asymmetry may be observed (one side appears to move more briskly and then appears more sluggish in comparison with the contralateral side) . Patients may also suffer from dysphagia and dysarthria.


Peripheral nerve


Peripheral nerve injury, specifically to the vagus nerve or the recurrent or superior laryngeal nerve branches, typically presents with absent or sluggish vocal fold movement. Proximal vagal injuries may also present with palatal and pharyngeal paralysis. Clinically, unilateral RLN paralysis typically presents as a breathy voice. Diplophonia and aspiration may occur .


Classically, paralysis of the SLN results in loss of a patient’s upper register . Normally, the CT muscle contracts briskly in falsetto or modal phonation to increase tension in the vocal fold . The inability to increase vocal tension results in poor vocal performance, especially at higher pitches . The clinical manifestations specific to SLN paralysis are likely more troublesome for singers and professional speakers . Moreover, the internal division of the SLN carries afferent fibers from the larynx to the central nervous system. This afferent input likely plays a role in vocal control and modulation .


More subtle paresis of the SLN or RLN may cause numerous voice complaints, including vocal fatigue, hoarseness, impairment of volume, loss of upper range, loss of projection, and breathiness. Vocal fatigue may be caused by the additional effort required to raise vocal pitch and project, and by hyperfunctional compensatory gestures. Patients who have either RLN or SLN paresis often develop a compensatory, hyperfunctional MTD to generate a “stronger” voice .


Other symptoms may occur with injury to the vagus or the laryngeal nerve branches. Hypoesthesia of the supraglottic larynx suggests injury to the internal division of the superior laryngeal nerve and may cause intermittent choking symptoms. Hypoesthesia in addition to pharyngeal dysfunction can place the patient at significant risk for aspiration . Neuralgia or paresthesia of the laryngeal nerves may also manifest as or contribute to chronic cough, globus, or laryngeal pain syndromes .


Dysphagia often occurs with vocal fold paralysis and paresis. Patients may aspirate, particularly if there is significant pharyngeal involvement. Injury to the SLN may result in dysphagia by several mechanisms. Injury to the internal division results in loss of afferent input to the swallowing center in the brainstem. In addition, recent evidence has suggested that the external division of the SLN may supply innervation to the cricopharyngeus. Denervation may result in cricopharyngeal dysfunction and subsequent dysphagia .


Laryngeal findings usually depend on which nerves are involved and the severity of injury. A vocal fold paralysis results in absent motion on the affected side. Vocal fold paresis may be more subtle. Vocal fold lag, or sluggishness, is the most common sign. This lag may only become apparent with repetitive tasks that cause the patient to fatigue. Asymmetry in motion should raise suspicion of a paresis, but does not always indicate which nerves in particular are involved . Supraglottic hyperfunction is often present in patients who have paresis and may make the examination more difficult to interpret. Efforts to try to relax or “unload” the hyperfunction may help in determining which muscles are affected. Asymmetry may be present in patients who have muscle tension dysphonia without paresis.


Vocal fold tone is variable after injury to the recurrent laryngeal nerve and depends on the degree of reinnervation. Reinnervation prevents muscle atrophy. Spontaneous reinnervation may occur after nerve transection. The source of the reinnervation is not known, but may include regenerating fibers from the transected RLN, the SLN, cervical autonomic nerves, and nerve branches innervating pharyngeal constrictors .


Should reinnervation occur after nerve transection, it is usually not detectable for about 4 months . The clinical course after 4 months is determined by the degree of reinnervation and synkinesis. Although reinnervation after a complete RLN transection prevents muscle wasting, typically it does not restore useful movement to the vocal fold because of synkinesis. Synkinesis results from nonselective reinnervation of adductor and abductor muscles. As a result, muscles that perform opposing functions contract simultaneously, resulting in immobility or hypomobility of the vocal fold. The clinical picture depends on the proportion of adductor and abductor fibers reinnervated and the ability of the contralateral vocal fold to compensate by crossing the midline of the glottis .


Myopathy


Myopathies may be inherited or result from metabolic or inflammatory processes . Isolated laryngeal myopathy is rarely reported, although chronic steroid inhaler use has been insinuated as a cause . Laryngeal findings include loss of muscle tone and hypomobility. These findings are similar to those that may be seen with motor neuropathy. Some have suggested that myopathy is underdiagnosed as a laryngeal disorder, because we tend to think more about nerve injuries when we see weak, flaccid vocal folds .




Manifestations of neurologic disease


Neurologic disorders may affect voice and speech production in several ways. Central injury may affect initiation, coordination, and quality of voice and speech. Direct effects on the larynx can affect glottic closure patterns and efficiency along with laryngeal muscle tone. Denervation of muscles involved in the support mechanism of the voice, such as the diaphragm or chest wall musculature, affects voice strength and quality. Dysfunction of oropharyngeal musculature may affect resonance. A palatal paralysis results in a more hypernasal voice. Impairment of cranial nerve V, VII, or XII function can affect articulation. Findings on general neurologic and laryngeal examination depend on which nerves are involved and where the disorder affects the neuromuscular pathway ( Table 1 ).



Table 1

Laryngeal and general findings of neurologic disease




























Site of lesion General findings Laryngeal/speech findings
Upper motor neuron Spasticity, hyperreflexia, rigidity, positive Babinski sign, myoclonus Spastic vocal fold paralysis/paresis, spastic dysarthria, laryngeal myoclonus
Lower motor neuron Weakness, flaccidity, fasciculations Flaccid vocal fold paralysis/paresis, glottic insufficiency, hypernasal speech, flaccid dysarthria
Extrapyramidal Tremor (pill-rolling in Parkinson’s disease), dystonia, dyskinesia, dysdiadochokinesia Vocal fold bowing, mid-fold insufficiency, tremor, laryngeal dystonia, dysdiadochokinesia
Peripheral nerve Weakness, atrophy, sensory deficits Hypomobility, immobility, ?atrophy (tone depends on degree of reinnervation)
Myopathy Weakness, flaccidity Hypomobility, flaccidity


Motor neuron diseases


Motor neuron diseases may result from degeneration of upper motor neurons, lower motor neurons, or both. When both upper and lower motor neurons are involved, the diagnosis of amyotrophic lateral sclerosis (ALS) or Lou Gherig’s Disease is made . ALS is fatal, usually from respiratory failure, but the clinical course is variable. Other examples of upper motor neuron disease processes include progressive lateral sclerosis and pseudobulbar palsy. Primary lateral sclerosis typically involves destruction of upper motor neurons only. The diagnosis is typically made after 4 years of predominantly upper motor neuron involvement . Pseudobulbar palsy results from interruption of bilateral corticospinal tract axons from other disease processes, such as stroke, multiple sclerosis, or tumor, as opposed to destruction of the neuronal cell body itself . Patients who have pseudobulbar palsy often have inappropriate emotional outbursts. A pseudobulbar palsy affect is often seen in patients who have ALS .


Lower motor neuron diseases include ALS, progressive bulbar palsy, and spinal muscle atrophy. Progressive bulbar palsy is essentially ALS affecting only the cranial nerves. Progressive spinal atrophy includes several autosomal-recessive disorders that involve degeneration of the anterior horn cells of the spinal cord. Although some forms present in adulthood, many present in younger patients .


Physical findings differ between upper and lower motor neuron processes. Upper motor neuron findings include spasticity of musculature and hyperreflexia. Spasticity of laryngeal musculature often results in a strained voice that might be misconstrued as spasmodic dysphonia. Patients may suffer from intermittent laryngospasm. Spasticity of oral musculature results in strained, effortful dysarthria. Myoclonus may occur. Extremity involvement may be noted. A positive Babinski reflex is a classic finding of upper motor neuron disease .


Lower motor neuron processes result in flaccid paralysis, muscle atrophy, and fasciculations. Patients may develop weak, breathy voices, bowing of the vocal folds, and poor cough. Palatal involvement may lead to nasal regurgitation and hypernasal speech. Pharyngeal musculature involvement leads to oropharyngeal dysphagia. Tongue and facial muscle involvement leads to slurred speech and oral dysphagia. With poor oral motor function, pharyngeal squeeze, and glottic incompetence, these patients are often at significant risk for aspiration .


Cerebrovascular accident


Cerebrovascular accidents may present with upper and lower motor neuron findings depending on the size and location of the stroke. Strokes may result from ischemia (secondary to thrombosis or hypotension) or hemorrhage. Unilateral cortical strokes are unlikely to result in complete vocal fold paralysis because of bilateral cerebral innervation of the laryngeal nerves. Brainstem stroke may cause vocal fold paralysis if disruption of the nucleus ambiguus or corticobulbar fibers synapsing with the nucleus ambiguus occurs. Isolated vocal fold paralysis secondary to stroke is rare. Wallenberg syndrome or lateral medullary syndrome results from occlusion of the posterior inferior cerebellar artery. It may result in some combination of vocal fold paresis or paralysis, decrease in ipsilateral facial pain and temperature, decrease in contralateral body pain and temperature, dysphagia, dysarthria, vertigo, Horner syndrome, ataxia, and hiccoughs . Stroke patients often are debilitated, which also contributes to poor voice quality. Abnormal body positioning and strength contribute to vocal problems. In addition, these patients often have significant dysphagia and are at high risk for aspiration pneumonia.


Extrapyramidal diseases


Diseases of the extrapyramidal system include Parkinson’s disease, spasmodic dysphonia, and laryngeal tremor. Parkinson’s disease is a movement disorder resulting from degeneration of dopamine-secreting cells within the substantia nigra of the brainstem. This process results in loss of the neural pathways through the basal ganglia that are involved in control of movement. Classic findings include tremor, rigidity, bradykinesia, and postural instability.


(Access Video on Parkinsonian Cogwheeling in online version of this article at: http://www.oto.theclinics.com/ .)


More than 70% of patients who have Parkinson’s disease have voice and speech manifestations. Patients who have Parkinson’s disease often have soft, breathy, monotonal voices. Laryngeal tremor is common. Patients often perceive their voice as normal. Affect is often flat (“masked”). In addition, patients who have Parkinson’s disease may have significant dysarthria and dysphagia. Characteristic laryngeal signs include vocal fold bowing, glottic insufficiency, and slow vibration. The glottic insufficiency and poor breath support attributable to debilitation and chest wall rigidity result in a soft, breathy voice quality .


Vocal fold paralysis should raise suspicion of a Parkinson plus syndrome, such as progressive supranuclear palsy, Shy-Drager syndrome, and multisystem atrophy. These disease processes are usually more rapidly progressing and less responsive to medication. In addition, patients who have multisystem atrophy are at risk for bilateral vocal fold paralysis and airway obstruction .


Spasmodic dysphonia


Spasmodic dysphonia (SD) is a focal dystonia the larynx. As with other dystonias, it is characterized by involuntary muscle contractions or spasms. These spasms are task-specific. Adductory spasmodic dysphonia (AdSD) accounts for 80% of the cases of SD, with abductory (AbSD) and mixed dysphonias occurring less frequently. Patients who have AdSD have a characteristic strained/pressed quality to their voices.


(Access Video on Adductor Spasms in online version of this article at: http://www.oto.theclinics.com/ .)


They suffer voice breaks with voiced consonants. Patients who have AbSD have spasms of the PCA muscle with voiceless consonants, resulting in intermittent breathiness .


(Access Video on Mixed adductor/abductor Spasms in online version of this article at: http://www.oto.theclinics.com/ .)


The pathophysiology of SD is uncertain. It may be attributable to dysfunction of the laryngeal feedback systems resulting in disinhibition of laryngeal muscle action . Laryngeal tremor may be present in addition to the dystonia. The combination of tremor and dystonia is referred to as dystonic tremor. These entities can be difficult to distinguish at times . Spasmodic dysphonia might also be difficult to distinguish from muscle tension dysphonia or other functional dysphonias.


Laryngeal tremor


Vocal tremor presents as nearly regular oscillations of the laryngeal and pharyngeal musculature.


(Access Video on Laryngeal Tremor in online version of this article at: http://www.oto.theclinics.com/ .)


The voice is unstable with frequent breaks. Tremor may be seen as a manifestation of several neurologic diseases, including Parkinson’s, ALS, and cerebellar diseases . Usually other neurologic signs and symptoms are present when a more severe neurologic disease is present. Tremor may also be seen with and is often difficult to distinguish from spasmodic dysphonia . When laryngeal tremor is present, a thorough neurologic evaluation is required, with assessment of cranial nerve, extremity, and cerebellar function and gait.


When no other signs or symptoms are present, vocal tremor is usually a manifestation of essential tremor, one of the most common causes of voice tremor. It may be the only manifestation, but typically the extremities are involved also. The voice is affected in approximately 20% of cases of essential tremor . In addition to the intrinsic laryngeal muscles, the extrinsic laryngeal muscles, pharyngeal muscles, and muscles of respiration may be involved. The pathophysiology of tremor is incompletely understood. Electromyograph studies have demonstrated that various laryngeal muscles may oscillate at different frequencies, suggesting multiple foci of central stimulus, or peripheral contribution to the oscillatory pattern by a reflex arc. In addition, there may be different degrees of severity amongst each of the laryngeal muscles .


Myoclonus


Segmental myoclonus may occur within the pharynx and larynx. Typically, involuntary, arrhythmic, jerk-like movements are seen. Usually it is bilateral, although it may occur unilaterally. Palatopharyngeal myoclonus may produce slow, regular voice arrests that may be missed in running speech. It may also be triggered by speech and result in more rapid, dramatic voice arrests . Myoclonus is believed most commonly to arise from dysfunction or lesions within the dentate, red, and inferior olivary nuclei. Unlike tremor, it typically does not involve opposing muscle groups. Myoclonus may be seen in neurodegenerative diseases .


Neuromuscular junction


Myasthenia gravis is an autoimmune disease characterized by muscle weakness exacerbated by repetitive use and improved with rest. Antibodies are produced to the postsynaptic acetylcholine receptor at the neuromuscular junction. Although ocular involvement is most common, laryngeal myasthenia may present independently or in conjunction with other muscles .


Laryngeal finding are best appreciated with fiberoptic laryngeal examinations. Vocal fold fatigability with repetitive phonatory tasks is characteristic. Fluctuating movement asymmetry may be observed (one side appears to move more briskly and then appears more sluggish in comparison with the contralateral side) . Patients may also suffer from dysphagia and dysarthria.


Peripheral nerve


Peripheral nerve injury, specifically to the vagus nerve or the recurrent or superior laryngeal nerve branches, typically presents with absent or sluggish vocal fold movement. Proximal vagal injuries may also present with palatal and pharyngeal paralysis. Clinically, unilateral RLN paralysis typically presents as a breathy voice. Diplophonia and aspiration may occur .


Classically, paralysis of the SLN results in loss of a patient’s upper register . Normally, the CT muscle contracts briskly in falsetto or modal phonation to increase tension in the vocal fold . The inability to increase vocal tension results in poor vocal performance, especially at higher pitches . The clinical manifestations specific to SLN paralysis are likely more troublesome for singers and professional speakers . Moreover, the internal division of the SLN carries afferent fibers from the larynx to the central nervous system. This afferent input likely plays a role in vocal control and modulation .


More subtle paresis of the SLN or RLN may cause numerous voice complaints, including vocal fatigue, hoarseness, impairment of volume, loss of upper range, loss of projection, and breathiness. Vocal fatigue may be caused by the additional effort required to raise vocal pitch and project, and by hyperfunctional compensatory gestures. Patients who have either RLN or SLN paresis often develop a compensatory, hyperfunctional MTD to generate a “stronger” voice .


Other symptoms may occur with injury to the vagus or the laryngeal nerve branches. Hypoesthesia of the supraglottic larynx suggests injury to the internal division of the superior laryngeal nerve and may cause intermittent choking symptoms. Hypoesthesia in addition to pharyngeal dysfunction can place the patient at significant risk for aspiration . Neuralgia or paresthesia of the laryngeal nerves may also manifest as or contribute to chronic cough, globus, or laryngeal pain syndromes .


Dysphagia often occurs with vocal fold paralysis and paresis. Patients may aspirate, particularly if there is significant pharyngeal involvement. Injury to the SLN may result in dysphagia by several mechanisms. Injury to the internal division results in loss of afferent input to the swallowing center in the brainstem. In addition, recent evidence has suggested that the external division of the SLN may supply innervation to the cricopharyngeus. Denervation may result in cricopharyngeal dysfunction and subsequent dysphagia .


Laryngeal findings usually depend on which nerves are involved and the severity of injury. A vocal fold paralysis results in absent motion on the affected side. Vocal fold paresis may be more subtle. Vocal fold lag, or sluggishness, is the most common sign. This lag may only become apparent with repetitive tasks that cause the patient to fatigue. Asymmetry in motion should raise suspicion of a paresis, but does not always indicate which nerves in particular are involved . Supraglottic hyperfunction is often present in patients who have paresis and may make the examination more difficult to interpret. Efforts to try to relax or “unload” the hyperfunction may help in determining which muscles are affected. Asymmetry may be present in patients who have muscle tension dysphonia without paresis.


Vocal fold tone is variable after injury to the recurrent laryngeal nerve and depends on the degree of reinnervation. Reinnervation prevents muscle atrophy. Spontaneous reinnervation may occur after nerve transection. The source of the reinnervation is not known, but may include regenerating fibers from the transected RLN, the SLN, cervical autonomic nerves, and nerve branches innervating pharyngeal constrictors .


Should reinnervation occur after nerve transection, it is usually not detectable for about 4 months . The clinical course after 4 months is determined by the degree of reinnervation and synkinesis. Although reinnervation after a complete RLN transection prevents muscle wasting, typically it does not restore useful movement to the vocal fold because of synkinesis. Synkinesis results from nonselective reinnervation of adductor and abductor muscles. As a result, muscles that perform opposing functions contract simultaneously, resulting in immobility or hypomobility of the vocal fold. The clinical picture depends on the proportion of adductor and abductor fibers reinnervated and the ability of the contralateral vocal fold to compensate by crossing the midline of the glottis .


Myopathy


Myopathies may be inherited or result from metabolic or inflammatory processes . Isolated laryngeal myopathy is rarely reported, although chronic steroid inhaler use has been insinuated as a cause . Laryngeal findings include loss of muscle tone and hypomobility. These findings are similar to those that may be seen with motor neuropathy. Some have suggested that myopathy is underdiagnosed as a laryngeal disorder, because we tend to think more about nerve injuries when we see weak, flaccid vocal folds .

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Apr 2, 2017 | Posted by in OTOLARYNGOLOGY | Comments Off on Neurolaryngologic Evaluation of the Performer

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