Practice Essentials
Laryngeal, or vocal, tremor is a common symptom of several neurologic disorders. Tremors are rhythmic, involuntary oscillating movements that, when the muscles of phonation are involved, have a disabling effect because of fluctuations in the amplitude and fundamental frequency of the voice. Vocal tremors involve not only tremor of the intrinsic muscles of the larynx but also, on occasion, the extrinsic laryngeal, pharyngeal, and palatal muscles, as well as the muscles of the diaphragm, chest wall, and abdomen (see the image below). Flexible laryngoscopy with videostroboscopy enables an assessment of the extent of vocal tremor and its location in the pharynx and larynx. Treatment depends on etiology, with management strategies including the use of behavioral therapy and botulinum toxin A (BTA). (See Etiology and Presentation.) [1, 2, 3]
Laryngeal cartilages, posterior view.
Neurologic disorders that can demonstrate a vocal tremor include the following [4] (see Presentation, Workup, Treatment, and Medication):
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Parkinson-plus syndromes - Including multisystem degeneration, Shy-Drager syndrome, basal ganglia degeneration, stroke, progressive supranuclear palsy
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Myasthenia gravis
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Ataxic disorders - Such as Friedreich ataxia
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Laryngeal dystonias
Vocal tremor in the absence of other neurologic disorders is called essential tremor of the voice (ETV). Tremors affecting the larynx can typically be divided into those that affect the voice at rest and those that affect the voice with action. Parkinson disease is often described as a resting tremor, whereas essential tremor of the larynx, as with the body, is an action/intention tremor. Although essential tremor is exaggerated during phonation, it can also be seen at rest as the laryngeal motion associated with respiration can cause an action tremor.
Signs and symptoms of laryngeal (vocal) tremor
A history of multiple neurologic findings may suggest that the laryngeal tremor is secondary to another disease. The patient should be asked about specific vocal symptoms, such as the following:
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Tremor
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Vocal fatigue
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Pain with speaking
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Increased effort
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Hoarseness
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Pitch breaks
Prevalence of laryngeal (vocal) tremor
Vocal tremor may be present in 25-30% of patients with essential tremor. Some reports describe vocal tremor in 66.7% of patients with adductor spasmodic dysphonia. A study by Patel et al found vocal tremor in 54.4% of patients with adductor spasmodic dysphonia and in 32.1% of those with abductor spasmodic dysphonia. [6] Perez et al report vocal tremor in 55% of patients with Parkinson disease and in 64% of patients with Parkinson-plus syndromes. [7]
Prognosis
The degree of disability caused by laryngeal tremor may range from mild to incapacitating vocal symptoms. Progression of neurologic disease may lead to dysphagia and an increased risk of aspiration pneumonia. (See Presentation.)
Essential tremor of the voice (ETV) is a chronic condition with no cure. Without treatment, symptoms slowly worsen over months and years in patients with laryngeal tremor. (See Treatment and Medication.)
Patient education
The patient must know that no cure for ETV exists and that the treatment for this chronic condition addresses only the symptoms.
Workup
Workup in laryngeal tremor includes the following:
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Laboratory tests - A complete blood count (CBC) and chemistry panel, thyroid function test, erythrocyte sedimentation rate, liver function test, and serum ceruloplasmin are indicated studies but are often low yield
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Flexible laryngoscopy with videostroboscopy - Enables an assessment of the extent of the tremor and its location in the pharynx and larynx; videostroboscopy may demonstrate the vibratory function and architecture of the vocal folds but is often difficult to obtain in severe tremor cases due to supraglottic compensatory hyperfunction
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Electromyography - May reveal tremor or increased muscle activity in patients with a confusing vocal picture and when spasmodic dysphonia is suspected in addition to tremor
Aerodynamic analysis is used to evaluate airflow and air pressure during voice production. Patients with adductor spasmodic dysphonia have higher than normal subglottic pressures and lower airflow rates, and aerodynamic analysis may help to differentiate ETV from a mixed case. Greater than normal airflow rates are seen during abductor spasms.
Acoustic analysis may be used to monitor the patient’s response to treatment.
Management
The treatment of vocal tremor depends on the etiology of the tremor. In Parkinson disease, for example, behavioral therapy can produce speech and voice improvements, while in adductor spasmodic dysphonia, botulinum toxin A (BTA) is the mainstay of treatment. BTA can also be used to treat ETV, although the results of this treatment in ETV have been mixed. Although systemic tremor symptoms can improve, the efficacy of other pharmacologic interventions for ETV is typically poor. [8]
Etiology
The larynx is under extensive neural control, and the physiology of phonation is complex. Several mechanisms have been implicated in the etiology of laryngeal tremor, including the interaction between a central oscillatory source and peripheral reflex loops.
As a rule, tremor results from a lesion that involves the extrapyramidal system or cerebellum. Electromyographic studies show that vocal tremor can arise from the involvement of muscles at any level of the speech production mechanism.
A study by de Lima Xavier and Simonyan, using functional magnetic resonance imaging (MRI), high-resolution MRI, and diffusion-weighted imaging, found that ETV and dystonic voice tremor broadly overlap with regard to cortical alterations. This included in the primary sensorimotor, inferior/superior parietal, and inferior temporal cortices, regions in which multisensory information is integrated during speech. [9]
However, in contrast to a laryngeal dystonia such as spasmodic dysphonia, which typically affects only the intrinsic laryngeal musculature, ETV that arises from the cerebello-olivary systems often affects a greater portion of muscles of the upper aerodigestive tract.
A study by Hemmerich et al indicated that the greater the severity of vocal tremor, the more structures in the pulmonary, laryngeal, velopharyngeal, and oral regions are involved. Mild vocal tremor was found normally to involve tremor in three laryngeal structures, while moderate vocal tremor involved five structures, contained in the laryngeal area and a second region, and severe vocal tremor involved eight structures, with all regions affected. Among the 20 persons in the study with vocal tremor, all of whom were adults, the most frequently (95%) and severely affected structures were in the larynx. [10]
Approximately 50% of cases of essential tremor are inherited in an autosomal dominant fashion.
Epidemiology
Measuring the true incidence of essential tremor is difficult because symptoms may be mild and go unnoticed in as many as 50% of affected people in the United States. Laryngeal dystonias are more prevalent in women, with a male-to-female ratio of 1:3-8.
Essential tremor is characterized by a bimodal age of onset, usually manifesting in the second and sixth decades of life. Parkinson disease is the most common movement disorder in patients older than 55 years, and dysphonia may be the initial symptom.
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Laryngeal cartilages, posterior view.
