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). (See Etiology and Presentation.) [1, 2, 3]
Neurologic disorders that can demonstrate a vocal tremor include the following  (see Presentation, Workup, Treatment, and Medication):
Ataxic disorders - Such as Friedreich ataxia
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.
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.  Perez et al report vocal tremor in 55% of patients with Parkinson disease and in 64% of patients with Parkinson-plus syndromes. 
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.)
The patient must know that no cure for ETV exists and that the treatment for this chronic condition addresses only the symptoms.
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.
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.
Approximately 50% of cases of essential tremor are inherited in an autosomal dominant fashion.
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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