Understanding Essential Tremor of the Voice
What is it?
Essential tremor of the voice is a form of essential tremor. Essential tremor is a neurological disorder (disorder of the central nervous system) that causes parts of the body rhythmically shake, due to an abnormal control of muscle contraction. When essential tremor affects the larynx and other structures involved in speech production (i.e. tongue, soft palate, pharynx, muscles of respiration), it results in essential tremor of the voice. Essential tremor of the voice results in involuntary periodic (regular), rhythmic changes in pitch and loudness of the voice and may be perceived as a “shaky” vocal quality. Many patients with essential tremor of the voice experience tremor in other parts of the body (i.e. limbs), however, some individuals can present with only tremor of the voice.
Characteristics of Essential Tremor of the Voice:
Essential tremor is the most common movement disorder. Essential tremor of the voice typically develops in middle age (50’s-60’s) and is onset is typically gradual. Severity of essential tremor typically progresses with age but rate of progression is often very slow. About one third to one half of cases of essential tremor of the voice are familial in type (meaning the individual with tremor has a relative with tremor).
The severity of the tremor (i.e. variation in the amplitude/strength of the tremor and the frequency (oscillations per second) may vary from person to person.
Symptoms may worsen in certain conditions like emotional stress, speaking on the phone, or fatigue. Tremor may be perceived by others as an individual sounding “nervous” due to the shaky quality of the voice. The vocal tremor may result in increased effort during speech production as one attempts to compensate for or manage the tremulous vocal quality and may present with decreased ability to be understood by others.
Essential tremor of the voice is not correlated with development of Parkinson’s Disease or the voice tremor that co-occurs with Parkinson’s Disease.
What is the cause of vocal tremor?
There is no known cause for essential tremor. Neurophysiological and genetic factors are not yet fully understood. Essential tremor of the voice is suspected to originate from dysfunction in the cerebellum in the brain. It is hypothesized that both genetic and environmental factors play a role in development of the disorder.
Diagnostic Tools:
Tremor can best be detected in sustained vowel notes like an “ah” held out for a period of time. You may notice vocal tremor more in sentences with more vowels.
A full diagnostic assessment is usually completed by both a speech language pathologist and otolaryngologist. You may be asked to read sentences that will collect acoustic measures, aerodynamic measures, and may be provided with tasks to help to differentially diagnose tremor from other similarly presenting disorders.
Location, extent, and severity of essential tremor of the laryngeal and pharyngeal structures may be seen on a flexible or rigid laryngoscopy exam, through the rhythmic movements of the laryngeal structures. Videostrobosopy during this exam will allow for visualization of tremor during phonation.
Differentiating essential tremor of the voice from other disorders:
Essential tremor of the voice can present with similar characteristics to a disorder called spasmodic dysphonia, which causes sound specific voice breaks. Sometimes tremor may be severe enough to elicit similarly presenting phonation stoppages as typically seen with spasmodic dysphonia. Similarly, symptoms of tremor may mask symptoms of spasmodic dysphonia and vice versa. Some individuals may have both essential tremor of the voice and spasmodic dysphonia. A person may also have secondary muscle tension dysphonia (MTD), develop as a compensatory method for the tremor.
See this post for differentiation tips.
Treatment options:
There is no standard treatment option for tremor at this time, as tremor cannot be cured. However, several treatment options exist for patients. Botulinum toxin injections are sometimes used to minimize the severity of tremor. Botulinum toxin functions to temporarily block the muscle contractions and temporarily “weaken” the tremor that typically occurs with muscle contraction.
Botulinum toxin injections are not as effective for tremor as they are for spasmodic dysphonia, however. This is partly due to the fact that many tremor patients have tremor in several structures that are involved with the dysfunctional speech.
Although voice therapy will not cure or take away the vocal tremor, voice therapy may be helpful to have patients learn how to more effectively compensate for the tremor. Using slowed speaking rate, more efficient airflow and resonance, and effective ways to project can help a person to work with the tremor rather than against it.
Medication to control essential tremor may also be recommended in some cases. Medication that is typically prescribed to control essential tremor in other parts of the body may not be as effective in managing essential tremor in the voice. Medication management in regards to essential tremor will be handled by a neurologist. Sodium Oxybate is currently being trialed as a potential medication to treat symptoms of vocal tremor.
Deep Brain Stimulation (DBS) (typically targeting the thalamus of the brain) has been proposed as a method to reduce symptoms of tremor. Long term research on this treatment method is ongoing.
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