Chapter 20

Laryngeal Anatomy

Laryngeal Function

Patient Evaluation

Clues to the cause of laryngeal weakness can be ascertained by analysis of a careful history that may include recent neck or mediastinal surgery, local trauma, tracheostomy, recent stroke, or transient ischemic attack. The neurologic examination includes assessment of language, cranial nerve function, muscle strength, cerebellar function, sensation, and tendon reflexes. Direct examination of the larynx should determine if the patient has normal sensation and reflex responses. In particular, the clinician should observe the pattern of breathing, the quality and character of phonation, and the active swallowing of liquids and solids.

Differential Diagnosis

Central Nervous System Disorders

Sporadic and Familial Amyotrophic Lateral Sclerosis

Motor neuron disease (MND) comprises a group of disorders characterized by progressive lower motor neuron (LMN) signs including weakness, wasting, and fasciculation, often with superimposed upper motor neuron (UMN) signs, including hyperreflexia, the Hoffman and Babinski signs, and clonus, the combination of which makes the diagnosis of ALS inescapable.1 About 10% of ALS cases are inherited as an autosomal dominant (AD) trait in adults, the majority of whom have bulbar oropharyngeal and laryngeal involvement. Onefifth of familial ALS (FALS-AD) cases are associated with mutations in the copper/zinc-dependent superoxide dismutase (SOD1) gene located on chromosome 21 in ALS1. Bilateral vocal cord paralysis was the presenting manifestation of ALS in one patient with ALS1 due to missense mutation resulting.² Paralysis of the abductor muscles of the vocal cords was reported in non-FALS.³

X-Linked Spinal Bulbar Atrophy

X-linked spinal bulbar atrophy presents with slowly progressive lower motor neuropathy in men, which, unlike ALS, is confined to the LMN, with a time course slower than in ALS, in association with gynecomastia and testicular atrophy. Affected patients can manifest laryngeal involvement. The molecular defect is an expansion of a CAG repeat in the first exon of the androgen receptor gene, which expands a polyglutamine tract within the receptor. As the length of the tract of CAG increases, the illness becomes more severe; however, it is not clear how the molecular lesion causes MND. One affected patient developed bilateral abductor vocal cord paralysis.4 Cranial MRI of the brainstem was normal. Direct laryngoscopy showed a complete paralysis of both vocal cords in the paramedian position. Respiratory distress improved after tracheostomy. Most experts agree that it is clinically important to perform a careful assessment of vocal cord function in patients with X-linked spinal bulbar atrophy, as in other similar patients because when found, vocal cord paralysis can shorten life expectancy.

Spinal Muscular Atrophy

Childhood spinal muscular atrophy (SMA) presents with significant bulbar involvement and vocal cord paralysis.5–8 Children with SMA type 1 or Werdnig-Hoffmann disease, present at birth or in the first few months of life with hypotonia, and LMN signs in the limbs and oropharynx, leading to death by 2 years of age from recurrent aspiration due to laryngeal paralysis and respiratory failure. Those with type 2 SMA achieve normal milestones up to approximately 8 months of age, including sitting, without support in spite of hypotonia, but they fail to walk normally and can display variable oropharyngeal involvement. Many affected children can survive into the third or fourth decade. Individuals with SMA type 3 or Wohlfart-Kugelberg-Welander syndrome, have an onset any time after 18 months, typically in late childhood and adolescence as a proximal neurogenic muscular atrophy that may be confused with limb girdle muscular dystrophy. There may be an elevated serum creatine kinase (CK). Such patients present with a waddling gait, lumbar lordosis, genu recurvatum, and protuberant abdomen, or may appear thin like a stick man. Childhood SMA manifests autosomal recessive (AR) inheritance and linkage to chromosome 5q11.2–13.3, in two genes, one for neuronal apoptosis inhibitory protein (NAIP) accounting for up to 67% of cases, and another, in the survival motor neuron (SMN) gene, which was found to contain greater than 98% of deletions. The protein product of SMN is known to interact with RNA binding proteins and may actually be a spliceosome. Distal hereditary motor neuronopathy type VII is an AD disorder characterized by distal muscular atrophy and vocal cord paralysis, linkage of which was established to chromosome 2q14 in a large Welsh pedigree.⁹ The management of the oropharyngeal, laryngeal, and respiratory symptoms in the various syndromes of MND includes airway protection and voice, which may be improved with local therapy of the vocal cords, cricopharyngeal muscle myotomy, tracheostomy, feeding gastrostomy, parasympatholytic drugs, and if necessary, laryngeal diversion, the primary disadvantage of which is the complete loss of phonation.¹⁰

Poliomyelitis

Acute poliomyelitis, now a rare cause of acute lower motor neuron paralysis in industrialized countries, is due to poliovirus infection of spinal anterior horn cells and other motor neurons. A minor illness occurs 1 to 3 days before onset of paralysis, with gastrointestinal complaints of nausea and vomiting, abdominal cramps, pain, diarrhea, and the systemic manifestations of sore throat, fever, malaise, and headache. The major illness, which includes all forms of central nervous system (CNS) disease caused by the poliovirus, including aseptic meningitis or nonparalytic polio, polioencephalitis, bulbar polio, and paralysis, follows the minor illness by 3 to 4 days. Such patients can present with stiff neck, back pain, photophobia, headache, tremulousness, obtundation, agitation, myalgia, cramps, fasciculation, and radicular pain. Bulbar poliomyelitis, which occurs in 10 to 15% of paralytic patients, involves cranial nerves VII, IX, and X and the medullary reticular formation, resulting in facial weakness, difficulty swallowing, and phonation, as well as variable respiratory difficulty, ataxic breathing, lethargy, obtundation, hypotension, hypertension, and arrhythmias. One reported patient with spinobulbar poliomyelitis had residual dysfunction of cranial nerves IX and X, producing bilateral vocal cord paralysis and recurrent aspiration.11 Critical glottic stenosis developed 28 years after the initial episode of poliomyelitis, which appeared to be related to fibrosis of the intrinsic laryngeal muscles and ankylosis of the right cricoarytenoid joint. Accordingly, significant upper airway obstruction may develop as a late complication in those with stable neurologic deficits and chronic immobility of the vocal cords.

Postpolio Syndrome

Of the approximately 250,000 survivors of the polio epidemics, up to a quarter experience progressive muscle weakness known as postpolio syndrome. Myopathic symptoms are associated with, in order of decreasing occurrence, fatigue, arthralgia, myalgia, muscle atrophy, cold intolerance, respiratory insufficiency, and dysphagia. Nine patients with postpolio syndrome were evaluated for swallowing complaints with comprehensive history, physical examination, acoustic voice analysis, and laryngeal videostroboscopic endoscopy, including three with laryngeal EMG12 that revealed some degree of phonatory and laryngeal deficit, and in those with prominent dysphagia, vocal cord paralysis. Bilateral vocal cord paralysis was noted in one affected patient with bulbar and spinal involvement beginning at age 13, resulting in left facial, vocal cord, and hemidiaphragm paralysis that was treated by mechanical ventilation.¹³ Thirty-five years later, she noted inspiratory and expiratory stridor, leading to respiratory failure and tracheostomy. Laryngoscopic examination revealed bilateral vocal cord paralysis with near-midline fixation of the cords and pooling of secretions. The syndrome was attributed to progressive bulbar motor neuron weakness. Three patients with prior polio infection who presented with new complaints, including slowly progressive dyspnea, dysphagia, and hoarseness, were evaluated by videostroboscopy and EMG that showed vocal cord abductor and adductor weakness, and recurrent posterior glottic web in one patient, and laryngeal muscle denervation and reinnervation in two others.¹⁴ Treatment was directed at attempting to maintain the airway and optimize vocal quality. One patient benefited from tacheostomy, one from vocal cord medialization, and one from resection of interarytenoid scarring. Three additional patients with laryngeal changes in postpolio syndrome presented with dysphonia, vocal weakness, and fatigue. All three manifested abnormalities on videostroboscopic and laryngeal EMG.

Syringomyelia

Laryngeal weakness with vocal cord paralysis occurs in syringomyelia.15–17 In one case there was progressive loss of the pharyngeal reflexes with pooling of secretions in the upper esophagus and lower pharynx, requiring endotracheal intubation and feeding jejunostomy.¹⁸ At cervical laminectomy, the cavity was drained and repaired with improvement of pharyngeal reflexes, but there was aspiration 2 days after cervical laminectomy. Presumably, the syrinx had extended into the brainstem to affect neurons of the nucleus ambiguus that normally control pharyngeal, laryngeal, and esophageal muscles. One 35-year-old patient who complained of noisy breathing for 15 years and had been treated for chronic asthma, developed acute breathing difficulty and was found to have stridor and bilateral abductor vocal fold palsy.¹⁹ A syrinx was found with associated type I Chiari malformation. Three other patients with communicating syringomyelia had acute presentations, including one with paraplegia, a second with acute respiratory distress secondary to bilateral vocal cord paralysis, and a third with symptoms of brainstem ischemia.²⁰ Each had a communicating spinal cord syrinx associated with a posterior fossa and foramen magnum region anomaly, including a large posterior fossa arachnoid cyst in one, and Chiari malformations in the other two. Syringobulbia was found to be the cause of laryngeal stridor in an 11-year-old patient who had chronic symptoms since birth, and suddenly died after development of respiratory obstruction due to vocal cord paralysis.²¹ Postmortem examination showed extensive bilateral syringobulbia with the greatest involvement in the nucleus ambiguus. Other brainstem tracts and nuclei were partially affected.

Arnold-Chiari Malformations

The classification of Arnold-Chiari malformations, now termed Chiari complex,22 is based on the relative position of the cerebellum and brainstem in relation to the foramen magnum and the upper cervical canal.²³ Types I and II are degrees of a similar abnormality in which a conical deformity of the posterior midline cerebellum and the elongated brainstem that lies at or below the foramen magnum. Type I is divided into a classic and myelencephalic form; symptomatic patients are treated with occipitocervical surgical decompression. One MRI classification designated Chiari malformation in association with syringomyelia as type A, and those with evidence of frank herniation of the cerebellar tonsils below the foramen magnum alone as type B.²⁴ Those with Chiari type II present with progressive hydrocephalus and typically require insertion of a cerebrospinal fluid (CSF) shunt. Chiari type III is associated with an occipitocervical cephalocele and severe CNS malformations. Chiari type IV designates patients with myelomeningocele and severe cerebellar hypoplasia, the most common of which is probably the Dandy-Walker malformation, in which a defect in the inferior vermis is congruent with a ventricuocele of the enlarged fourth ventricle. Adults and infants alike can present symptomatic laryngeal symptoms.

The Arnold-Chiari malformation, in association with myelomeningocele, was considered the cause of progressive choking, apnea, and aspiration of 42 infants.²⁵ Shunts were already in place and were thought to be functioning normally; however, at posterior fossa craniotomy, all had compression of the upper spinal cord. Mortality was highest (71%) in infants with rapidly progressive, irreversible symptoms. The Arnold-Chiari malformation and shunted myelomeningocele presented with adductor vocal cord paralysis and loss of laryngeal sensation for 10 months.²⁶ In that infant, consideration was not given to posterior fossa exploration; treatment was supportive, including gastrostomy and close observation for several years. Bilateral abductor vocal cord paralysis due to Arnold-Chiari formation should be suspected in neonates and infants who present with high-pitched inspiratory stridor and airway compromise.²⁷ Unilateral vocal cord paralysis suspected in an infant or child with hoarse voice, low-pitched cry, and breathy cry or voice should be evaluated with direct laryngoscopy with flexible fiberoptic nasopharyngolaryngoscope and photodocumentation using a videocassette recorders.

Chiari malformation was suspected in a previously healthy 13-year-old boy without myelodysplasia who had mild scoliosis and complaints of nasal congestion, noisy nighttime breathing, and difficulty sleeping.²⁸ Flattening of the inspiratory loop on the flow-volume curve was found on pulmonary function testing, suggesting a variable extrathoracic obstruction due to a laryngeal lesion. Bilateral abductor vocal cord paralysis and sleep apnea developed precipitously following general anesthesia. Chiari malformations were discerned among six children by T1- and T2-weighted MRI with syndromes of failure to thrive, velopharyngeal incompetence, gastroesophageal reflux, or vagal hypertonia, leading to laryngeal obstruction due to vocal cord paralysis, paradoxical vocal cord motion, or laryngomalacia,²⁹ and treated symptomatically before decompressive surgery, which led to full functional recovery in five children. Adults likewise present with symptomatic vocal cord paralysis due to type I Chiari malformations.³⁰ Similarly, stridor and bilateral abductor vocal fold palsy was noted as well in a 35-year-old with complaints of noisy breathing for 15 years previously treated for chronic asthma¹⁹; subsequent evaluation revealed syringomyelia with a Chiari type I malformation.

Linder and Lindholm³¹ evaluated children born with a Chiari II malformation during their first 18 months; four of the 22 children studied by flexible fiberscopes had disturbed breathing, and among those, two suffered from central apneic attacks as well as bilateral vocal fold motion impairment, one from apneic spells only, and one from bilateral vocal fold motion impairment. All four had dysphagia with aspiration and respiratory symptoms within the first 3 to 6 months of life. One infant with severe symptoms expired at age 3 months. The vocal fold paralysis, apneic spells, and swallowing difficulties of another infant resolved following neurosurgical intervention. Choi and coworkers³² studied airway abnormalities in 16 patients with type I and eight patients with type II Chiari malformation. Vocal cord impairment was noted in three patients with type II Chiari, including one each with unilateral paralysis, bilateral paresis, and paralysis, but in none of those with type I disease. Tracheostomy was necessary in three, all Chiari type II; Central sleep apnea was noted in five of six patients, and tracheostomy was needed in three patients, all with type II malformations, but in none of those with type I disease.

Stroke

Laryngeal dysfunction occurs with infarcts of the brain, especially of the medulla. Venketasubramanian and colleagues33

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