Essential tremor (ET) is most commonly apparent as uncontrollable shaking of the hands, especially during deliberate movement. In addition to hands, ET can also affect the larynx (the hollow muscular organ in the throat that holds the vocal cords), soft palate, base of the tongue, other muscles of the throat and breathing musculature with the result of a quivery voice. This is called voice tremor, and is as much a movement disorder as shaking hands. However, other neurological disorders such as Parkinson’s disease can also cause voice tremor. Or, it may be seen as “isolated voice tremor.”
ET is frequently misdiagnosed
In January, 2018 the International Parkinson and Movement Disorder Society published a consensus statement that classified tremors according to their characteristics.[i] Part of their purposes was to help with clinical diagnosis, since ET is initially misidentified all too often. The task force that developed the statement defined ET as a “tremor syndrome of bilateral [both sides] upper limb action tremor with or without tremor in other locations (e.g., head, voice, lower limbs) …” in absence of any other neurological disorder. They excluded isolated focal (one location) tremors of the voice, head, task- and position-specific tremors from being classified as ET. They also specified that for diagnostic purposes, at least three years should pass without other neurological symptoms showing up that may suggest the presence of a condition or disease beyond solely essential tremor. (If you’re wondering what a person is supposed to think is wrong with them during that 3-year waiting period, the task force recommends calling it “indeterminate tremor.”)
Is voice tremor ET or isn’t it?
Julie Barkmeier-Kraemer, PhD, is a professor in the University of Utah Medical School, Division of Otolaryngology, and adjunct professor in the Department of Communication Science and Disorders. Since her specialty includes disorders of the larynx, she proposes that the task force reconsider excluding “isolated voice tremor” from the classification of ET, and instead view it as an ET variant.[ii] To establish her persuasive case, she analyzed 30 published studies of voice tremor.
Dr. Barkmeier-Kraemer points out that numerous parts of throat and breathing anatomy can be subject to ET-related oscillations, but the majority of the 30 studies dealt primarily with the larynx alone and its tremulous voice production. She hypothesizes that this emphasis on acoustic (sound) production has reinforced the idea of voice tremors as isolated. Despite the fact that many of the papers confirm that affected individuals are already diagnosed with ET—or they lack a diagnosis of a different neurological condition that could produce voice tremors—on balance the published literature doesn’t contain “systematic description of participant’s duration of disease, family history, duration of vocal tremor, age of onset, activation condition(s), body distribution, and other important information” that would indicate their voice tremor is a component of their ET. Only 3 out of 30 studies had sufficient characterization details to “assure accurate classification.”
Another aspect of her case for reconsidering voice tremor as an ET variant comes from data on when voice tremor began in relation to hands or other body parts. There is a current bias or assumption that the upper extremities are affected first with eventual tremor spread upwards to the head, neck and voice. However, the reverse was true for nearly 70% of participants in one study who reported that voice tremors occurred first (and were deemed “isolated voice tremor”) but eventually the hands or other parts of the body became involved so they then met the inclusion criteria for ET.
In addition to all the other difficulties that make it challenging to correctly diagnose ET, many older people with voice tremors assume that they are a normal part of aging-related physical changes and don’t seek treatment. For those who do, Dr. Barkmeier-Kraemer states that they “…frequently have co-occurring neurological diagnoses with the majority having ET followed by dystonia (e.g., spasmodic dysphonia) and other neurodegenerative diseases (e.g., Parkinson’s disease, cerebellar degeneration, and myasthenia gravis).” Furthermore, individuals with ET who turn to pharmaceuticals or neurosurgery to control their hand tremors—but they also have voice tremor—find that their voice tremors incidentally improve when the treatment helps their hand function.
Based on Dr. Barkmeier-Kraemer’s thoughtful and well-organized presentation of her analysis of 30 articles, it makes sense that for individuals with “isolated voice tremors” taking the time to gather detailed family and clinical history, and embracing the 3-year waiting period to see what else shows up (or doesn’t), a full diagnosis of ET may well be in order.
NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you have health concerns or questions of a personal medical nature.
[i] Bhatia KP, Bain P, Bajaj N, Elble RJ et al. Consensus Statement on the classification of tremors. from the task force on tremor of the International Parkinson and Movement Disorder Society.Mov Disord. 2018 Jan; 33(1):75-87.
[ii] Barkmeier-Kraemer, JM. Isolated Voice Tremor: A Clinical Variant of Essential Tremor or a Distinct Clinical Phenotype? Tremor Other Hyperkinet Mov (N Y). 2020; 10: 10.7916/tohm.v0.738.