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Essential tremor is a disease of involuntary movement that causes an affected region, most often the arms and hands, to shake while attempting use. This can make it difficult to write, handle eating utensils, or perform other necessary day-to-day activities. Essential tremor can also involve the larynx, vocal folds and throat - causing changes in the voice.
The cause of essential tremor is unknown, but it is inherited from a parent in nearly half of all cases. Essential tremor tends to worsen with age.
Essential vocal tremor causes rhythmic changes in loudness and/or pitch, which vary in severity. In cases of mild tremor, there may only be minor quavering in the voice. More severe tremor can actually cause interruptions in sound production. Variations in loudness (and sometimes in pitch) caused by essential voice tremor are rhythmic and always present, no matter the type of vocalization. Those with voice tremor may adopt whispering as a standard mode of speaking, as it masks these variations.
When severe, essential voice tremor can easily be confused with spasmodic dysphonia. This is a frequent diagnostic error, likely because many physicians do not realize that essential vocal tremor can cause such dramatic voice changes. By contrast, spasmodic dysphonia vocal cord contractions: are not usually rhythmic, do not appear during breathing, and may not appear during special types of voicing like singing. In addition, spasmodic dysphonia rarely extends beyond the larynx to involve the tongue and palate. Essential voice tremor is rhythmic and present across all voice tasks.
Essential tremor is a rhythmic, alternating contraction of opposing muscles. This results in oscillatory movement of the affected body part. When tremor affects the voice, it usually involves not only the vocal folds, but also the muscles of the pharynx, palate and back of the tongue. The vocal cords flutter open and closed during voicing, and also sometimes during quiet breathing. The cycle typically occurs four to twelve times per second. This motion is synchronized with similar muscle activity in all affected areas.
There is no specific test with which to diagnose essential voice tremor. Diagnosis is based on the observation of the typical vocal cord movements during voicing. The presence of essential tremor in the head or the hands is suggestive, although it is not required to make the diagnosis. It is not widely known, even among doctors, that essential tremor may affect only the voice.
There is no single, accepted treatment for essential voice tremor. Usually, the choice lies between medication and injections of botulinum toxin. Voice therapy typically offers little relief, because the vocal fold motion is involuntary.
When it affects other parts of the body, essential tremor sometimes responds to medication. Propranolol, usually used to control blood pressure, and primidone, a seizure medication, are common prescription drugs used for treatment. Neither of these has been clearly shown to help people with essential voice tremor in studies, but they may help in individual cases. Each has important side effects that should be discussed with a physician prior to use.
Botulinum toxin is a naturally-occurring substance which weakens muscle. Within laryngology, it enjoys its greatest use in the treatment of spasmodic dysphonia. It can be helpful with severe cases of essential tremor, by means of injection into the vocal folds though the skin of the neck, to even out the voice and make speaking less effortful. The effect is temporary, and injections need to be repeated every three to four months. While its effect in essential tremor is not as dramatic and complete as it is in spasmodic dysphonia, some patients benefit substantially.
In addition to an otolaryngologist, who is able to inform patients regarding botulinum toxin injections, individuals with essential voice tremor are advised to discuss treatment options with a neurologist, who will likely be able to give them the best and latest information on available medication. It is important to understand that, although both treatment options are designed to provide relief from symptoms, neither can cure the tremor.