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Neurologic disorders of the larynx may be focal diseases or local manifestations of systemic disorders. Characteristic deficiencies found on clinical examination may aid in ascertaining the site of a lesion.
Hyperfunctional disorders include dystonia, myoclonus, essential tremor, stuttering, and muscle tension dysphonia.
Hypofunctional disorders include focal disorders, such as vocal fold paresis and paralysis, and central causes such as Parkinson disease, multiple sclerosis, neuromuscular junction disorders, poliomyelitis, myopathies, medullary disorders, and psychogenic disorders.
Spasmodic dysphonia is an idiopathic focal laryngeal dystonia characterized by either halting or breathy speech breaks.
Botulinum toxin is an important treatment for spasmodic dysphonia and other dystonias.
Vocal fold paresis can result from trauma, tumor, or neurologic, idiopathic, or other medical diseases. Vocal fold positioning can vary on presentation.
Neurologic conditions that affect the larynx span a wide spectrum. They may be focal diseases or local manifestations of systemic disorders. These lesions can produce stereotyped patterns of abnormal function that the otolaryngologist should strive to recognize. Evaluation should include a complete head and neck examination, neurologic examination, and visual recording of the functional disability for documentation. For systemic disorders, consultation with a neurologist is useful for diagnosis and optimizing medical management. In general, neurologic dysfunction results from one or more insults within the central or peripheral nervous system.
A few important generalized neurologic disorders are characterized by specific patterns of involvement of the larynx and pharynx. In early stages of involvement, patients with these disorders may consult otolaryngologists, because symptoms are located in the head and neck region. At any stage of these disease processes, otolaryngologic consultation may be vital to differentiate manifestations of the disease from problems caused by other concurrent disorders to ensure appropriate management. The neurologic disorders that affect the larynx are best understood when characterized as either hyperfunctional or hypofunctional disorders ( Box 57.1 ). Although this is a general categorization, often both types can exist concurrently, particularly when hyperfunctional activity, such as muscle tension dysphonia, works to overcome a hypofunctional deficit.
Cortical lesions may result from strokes, tumors, or trauma and may impair the planning and execution of actions. Because of the diffuse and bilateral representation of laryngeal structures in the cortex, these lesions can result in aphasia, aphonia, dysarthria, dysphonia, and stridor. Extrapyramidal system defects are characterized by abnormal motor control, which may manifest as inappropriate or excessive muscle tension, tremor, and involuntary spasmodic muscle contractions, which vocally translates into strain, arrests, pitch breaks, and pitch instability. The dysfunction may be focal, regional, or generalized. In addition to problems caused by tumors or trauma, the extrapyramidal system is disrupted by conditions of uncertain etiology such as Parkinson disease (PD), tremor, and dystonia. Cerebellar lesions impair coordination of motor activities. In that instance, problems are generalized rather than focal. “Scanning speech” is regarded as characteristic of cerebellar involvement. Diagnosis is based on the presence of attendant physical signs, such as intention tremors, dysdiadochokinesia, dysmetria, ataxia, and nystagmus. Brainstem lesions result in flaccid paralysis. Because the cranial motor nuclei are densely packed within the brainstem, lesions at this level affect multiple outputs. Strokes and tumors of the brainstem produce severe dysfunction related to paralysis of the larynx, pharynx, or tongue and are associated with sensory deficits. The site of the lesion is best identified from the type of motor disruption, because observable clinical signs are predominantly disruptions of motor acts ( Table 57.1 ). Diffuse central nervous system lesions result from specific neurologic disorders, such as multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS) and have a myriad of signs and symptoms. Patients with movement disorders have a paucity of movement (akinesia or bradykinesia), excessive or hyperfunctional movement (hyperkinesia), or a combination of the two. The hyperkinetic motor programming errors can produce spasms, tremors, jerks, or tics, and symptoms related to the body part involved. For those with laryngeal manifestations, a multidisciplinary approach that includes the involvement of an otolaryngologist, neurologist, and speech pathologist is key to successful diagnosis and management of hyperfunctional disorders of the larynx (see also Chapter 57).
Site of Lesion | Signs |
---|---|
Cortex | Aphasia Aphonia Dysarthria Dysphonia Stridor |
Extrapyramidal system | Vocal strain and pitch breaks Tremor Spasmodic movements Focal, regional, or generalized dystonia |
Cerebellum | Ataxia Dysmetria Tremor Incoordination |
Brainstem | Flaccid paralysis Never isolated |
Dystonia is a syndrome dominated by sustained contractions of skeletal muscles that frequently cause twisting and repetitive movements or abnormal postures that may be sustained or intermittent. Because the condition is rare, and the movements and resulting postures are often unusual, dystonia is among the most commonly misdiagnosed neurologic conditions. The prevalence is unknown, but an estimated 200,000 to 300,000 cases of idiopathic dystonia occur in the United States. Classification is important, because it can inform prognosis and the approach to management. The classification scheme is outlined in Table 57.2 .
Axis | Dimension for Classification | Subgroups |
---|---|---|
Axis I: clinical features | Age at onset | Infancy (birth to 2 years) |
Childhood (3–12 years) | ||
Adolescence (13–20 years) | ||
Early adulthood (21–39 years) | ||
Late adulthood (40 years and older) | ||
Body distribution (see also Box 57.2 ) | Focal (one isolated body region) | |
Segmental (two or more contiguous regions) | ||
Multifocal (two or more noncontiguous regions) | ||
Hemidystonia (half the body) | ||
Generalized (trunk plus two other sites) | ||
Temporal pattern | Disease course (static vs. progressive) | |
Short-term variation (e.g., persistent, action specific, diurnal, or paroxysmal) | ||
Associated features | Isolated (with or without tremor) | |
Combined (with other neurologic or systemic features) | ||
Axis II: etiology | Nervous system pathology | Degenerative |
Structural (e.g., focal static lesions) | ||
No degenerative or structural pathology | ||
Heritability | Inherited (e.g., sex linked or autosomal, dominant or recessive, or mitochondrial) | |
Acquired (e.g., brain injury, drugs/toxins, vascular, or neoplastic) | ||
Idiopathic | Sporadic | |
Familial |
Dystonia can begin at nearly any age. Initial signs have occurred as early as 9 months and as late as 85 years. In general, onset has a bimodal distribution, with peaks at ages 8 and 42 years. As can be seen in Table 57.2 , patients are partly categorized according to symptom distribution. Focal dystonia involves one isolated body region, segmental disease involves two or more contiguous regions, multifocal disease involves two or more noncontiguous regions, hemidystonia involves half the body, and generalized dystonia is widespread including the trunk plus two other sites. The more common examples of focal dystonia are listed in Box 57.2 .
Focal
Blepharospasm (forced, involuntary eye closure)
Oromandibular dystonia (face, jaw, or tongue)
Torticollis (neck)
Writer's cramp (action-induced dystonic contraction of hand muscles)
Spasmodic dysphonia (larynx)
Segmental (cranial, axial, or crural)
Multifocal
Generalized (ambulatory, nonambulatory)
History, physical examination, and laboratory studies may fail to identify the cause of a patient's dystonic symptoms (idiopathic dystonia). This is a diagnosis of elimination that requires a normal perinatal and early developmental history; no history of neurologic illness or exposure to drugs known to cause acquired dystonia (e.g., phenothiazines); normal intellectual, pyramidal, cerebellar, and sensory examination findings; and normal diagnostic study results.
Because up to 16% of patients with dystonia and primary laryngeal involvement experience dissemination of the disease to another body part, patients should be advised of this potential and should be reexamined on a regular basis for signs of other dystonic involvement. Approximately 10% of patients with primary laryngeal dystonia have a family history of dystonia.
In most cases of childhood-onset idiopathic dystonia, family studies show an autosomal-dominant inheritance with reduced penetrance. A marker for some cases of childhood-onset dystonia has been found on chromosome 9. Heterogeneous genetic patterns among patients with idiopathic dystonic symptomatology have been reported, including a linkage to the X chromosome and Parkinsonism, and a dopamine-responsive form. Family and linkage studies, as well as genomic research, have recently identified multiple subtypes of dystonia with different genetic bases. Inherited primary monogenic dystonia can be broadly categorized into three phenotypic variants: primary torsion dystonia, which exhibits dystonia as the only clinical sign besides tremor ( DYT1, 2, 4, 6, 7, 13, 17, 21, 23, 24, 25, 27, and 28 phenotypes); dystonia plus, which can manifest with additional signs such as dopa-responsive Parkinsonism or myoclonus ( DYT3, 5 [formerly 14 ], 11, 12, 15, 16, and 26 phenotypes); and paroxysmal forms of dystonia and dyskinesia ( DYT8, 9, 10, 18, 19, and 20 phenotypes).
Clinically, spasmodic dysphonia is an idiopathic focal dystonia of the larynx. Although the disease was initially described by Traube in 1871, Fraenkel and Gowers later recognized the relationship with other dystonias, such as writer's cramp. Approximately 80% of cases of laryngeal dystonia have adductor spasmodic dysphonia (ADSD), whereby spasmodic adduction of the vocal folds during speech results in a strained and strangled voice. Fewer patients, around 20%, have abductor spasmodic dysphonia (ABSD), with intermittent or sustained opening of the larynx during speech that leads to breathy voice breaks or a whispering voice. Some patients display a combination of adductor and abductor signs and have been classified as having “mixed laryngeal dystonia.” Two other rare forms of laryngeal dystonia include adductor breathing dystonia and singer's laryngeal dystonia. In the former, patients adduct their vocal cords while inspiring. The glottic adduction causes stridor and dyspnea, but this is typically self-limited, does not cause hypoxia, and does not warrant surgical airway management. Singer's dystonia is the presence of symptoms only during singing. These patients have almost always been performing professionally as singers, and in some, the symptoms progress to also involve their speaking voice. Patients with more generalized dystonia, which also involves the larynx, have vocal dysfunction that is clinically indistinguishable from idiopathic spasmodic dysphonia. Meige syndrome, a regional dystonia of the head and neck, may be evident in those with blepharospasm, oromandibular dystonia, torticollis, or spasmodic dysphonia.
In all types of laryngeal dystonia, patients have anecdotally reported that symptoms momentarily improve when they pinch the nares, press the hand against the back of the head, press the hand into the abdomen, pull on an ear, or touch the clavicular notch. Many patients observe that they speak better after a yawn or sneeze or when they sing or yell; these sensory tricks or “geste antagoniste” are also common for patients with other craniocervical dystonias. There is no current cure for spasmodic dysphonia but a variety of treatments exist. Dedo and Izdebski described dramatic relief of symptoms with sectioning of the recurrent laryngeal nerve. The initial favorable reports were temporized by a review of 33 patients by Aronson and DeSanto that addressed surgical management. Three years after surgical treatment, only 36% of patients had some persistent improvement, and only 3% achieved a persistent normal voice. Selective laryngeal adductor denervation-reinnervation (SLAD-R) surgery for ADSD has shown outcomes similar to those with botulinum toxin (BoNT) for surgeons experienced with the procedure. However at present, the symptoms are most consistently managed with use of an individualized regimen of chemodenervation with BoNT into the involved muscles.
The bacterium Clostridium botulinum produces eight immunologically distinct toxins that are potent neuroparalytic agents: A 1-8 , B 1-8 , C 1 , D , D c , E 1-12 , F 1-8 , G, and H. BoNT exerts its effect at the neuromuscular junction by inhibiting the release of acetylcholine, causing a flaccid paralysis. Botulinum toxin type A, onabotulinumtoxin A (Botox; Allergan, Irvine, CA), abobotulinumtoxin A (Dysport; Galderma, Fort Worth, TX), or incobotulinumtoxin A (Xeomin; Merz Pharma GmbH, Frankfurt, Germany), is most commonly used. Botulinum toxin type B, rimabotulinumtoxin B (Myobloc; Solstice Neurosciences, San Francisco, CA) is also commercially available for clinical application.
Although BoNT has been used therapeutically in humans since the mid-1970s without evidence of a direct effect on uninjected muscles, the later consequences of long-term injections are unknown. Weakness and routine electromyography (EMG) changes in muscles distal to the site of injection have not been reported. However, abnormalities are detectable on single-fiber EMG. It is not known how long these abnormalities persist or whether they have any clinical significance. A paucity of data exists regarding use of BoNT during pregnancy; currently, injection is avoided in pregnant or lactating patients. Caution is warranted for the management of patients with conditions such as myasthenia gravis, Lambert-Eaton syndrome, and motor neuron disease, particularly when large doses are required, such as in the management of cervical dystonia. However, the amount of toxin that enters the circulation after injection is thought to be minute, and this theoretic concern should be balanced against the severity of the hyperkinetic symptoms.
In patients with ADSD, BoNT injection into the thyroarytenoid-vocalis muscle complex has been demonstrated to improve speaking to 60% to 100% of normal function, with a mean of 90%; the duration of effect was between 3 and 4 months. Adverse effects include a mild breathy dysphonia for less than 2 weeks (45%), mild choking on fluids for the first several days (22%), hyperventilation and dizziness when trying to speak while hypophonic, a sore throat or hemoptysis, and itching (without rash). In patients with ABSD, injection of BoNT into the posterior cricoarytenoid (PCA) muscle produces marked improvement, with a return to mean maximal functional performance of 70% of normal. Adverse effects include mild dysphagia without aspiration and mild stridor on exertion.
The effective treatment dose is variable for each patient and for each muscle injected; therefore injections are individualized. The dose range for ADSD is 0.05 to 20 units of BoNT, with an average dose of less than 1 unit per vocal fold. In general, a starting dose of 1.0 unit in 0.1 mL of saline is used for bilateral thyroarytenoid injections. Subsequent doses are varied according to clinical response and adverse effects, but over time the dose range of BoNT appears to be stable in the majority. Injections are given by means of a tuberculin syringe with a 27-gauge monopolar Polytef-coated hollow EMG recording needle. EMG guidance has the advantage of controlled administration into the more actively contracting regions of the muscle.
Adductor laryngeal injections are performed percutaneously through the cricothyroid membrane and into the thyroarytenoid–vocalis muscle complex, with use of EMG guidance for optimum placement ( Fig. 57.1 ). Injections for ABSD are administered to the PCA muscle ( Fig. 57.2 ). The physician reaches the muscle by manually rotating the larynx, placing the EMG needle behind the posterior edge of the thyroid lamina, and advancing the needle to the cricoid cartilage to arrive at the PCA muscle. Alternatively, a transcricoid injection can be made. When the patient is instructed to sniff, which maximally uses the PCA muscle, a burst of activity is seen on the EMG, and the toxin is administered. Some patients, particularly with ADSD, may present with supraglottic squeeze during the course of their treatment. In this instance, if nonresponsive to voice therapy, the supraglottic portion of the lateral cricoarytenoid muscles can be injected via a thyrohyoid approach.
The adverse effects previously described are transient and are caused by an extension of the pharmacology of the toxin. If the patient has a strong response to therapy, and too much weakness occurs, strength gradually returns. Follow-up therapy is carefully individualized, and the response to therapy should be meticulously documented.
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