Elan D. Louis, MD, MS,
Department of Neurology, University of Texas
Southwestern Medical Center,
Dallas, Texas
One question my patients with essential tremor (ET) often ask me is “how common is essential tremor?”
Knowing the answer to this question is important because it helps patients place what they are experiencing into some sort of larger context.
To answer this question, I go to the scientific literature for the answer. In a paper by Louis and McCreary published in 2021 in Tremor and Other Hyperkinetic Movements, the authors reviewed data from each of the 42 published population-based epidemiological studies of ET. These 42 studies were published over a 60-year period, from 1960 to 2020, and provided data from 23 countries in six continents on the “prevalence” of ET (i.e., the percentage of people in a given population who have ET).
The paper used two methods to analyze data from these 42 studies. Using one method, they calculated that 1.33% of all people of all ages have ET; using the second method, the values they obtained ranged from 0.4% to 0.67%. To simplify, if one combines these values from each method, then a “take-home” message is that approximately 1% of people, including people of all ages, have ET.
This information is of value; however, we all know that the chances of developing ET increase with age, and the same epidemiological studies tell us that the bulk of patients who have ET are age 65 and older. In the same paper, Louis and McCreary again used two methods to analyze data from the 42 epidemiological studies, and found that 5.79% to 8% of individuals age 65 and older had ET, and that in older age groups (e.g., individuals in their 90s), several epidemiological studies had reported that 20% or more had ET. The paper also noted men and women were equally likely to develop ET. This value, 5.79% – 8% of individuals age 65 and older, should be placed in a broader context. This value is similar to and even somewhat greater than the percentage of people in a similar age group who have Alzheimer’s disease (4.8%), indicating the high prevalence of ET.
Above, we have been discussing the percentage of people who have ET; however, we have not been discussing the actual number of people who have ET. What is that number? In an earlier study, published in 2014 in Tremor and Other Hyperkinetic Movements, Louis and Ottman used data from all available epidemiological studies to estimate the number of individuals in the United States who had ET. Their estimate ranged from 6.38 million to 7.63 million (average = 7.01 million), meaning that approximately 2.2% of the entire US population has ET. These are remarkably high numbers and percentages.
These numbers are significant, but they are not the only numbers that underscore the high disease burden ET carries. Above, we discussed “prevalence”, which is the percentage of people in the population who have ET. Another epidemiological term is “incidence”. This is the number of people who develop ET each year. It is a measure of the rate at which new ET cases are arising on a yearly basis rather than the number of patients who currently have ET. A population-based study of the incidence of ET was conducted in Spain on 2005 among persons age 65 and older. In that study, the authors reported that among persons age 65 and older, 616 per 100,000 developed ET each year. Stated in another way, one would expect 616 new ET cases arising each year among each 100,000 individuals in the population age 65 and older. There are approximately 55 million Americans age 65 and older. If 616 new cases are expected each year for every 100,000 of these, then approximately 333,000 new ET cases would be expected to arise each year among the approximately 55 million Americans age 65 and older. This is equivalent to 27,750 new ET cases per month or 925 new ET cases per day. Another “take home” message is that we can estimate that approximately 1,000 new ET cases arise in Americans age 65 and older each day.
Now we return to the initial question. How common is ET? It is very common. Data on the prevalence and incidence of ET are important. They serve to underscore how common ET is and how many people it affects in the population – indeed, ET is a medical issue with significant human and public health impact. An ET patient is not alone. Armed with this knowledge of the high prevalence of ET, physicians and scientists are better positioned to convince funding bodies of the value of ET research. Such research is needed in order to better understand the causes of ET and to eventually devise more effective treatments.
Now we return to the initial question. How common is ET? It is very common. Data on the prevalence and incidence of ET are important. They serve to underscore how common ET is and how many people it affects in the population – indeed, ET is a medical issue with significant human and public health impact. An ET patient is not alone. Armed with this knowledge of the high prevalence of ET, physicians and scientists are better positioned to convince funding bodies of the value of ET research. Such research is needed in order to better understand the causes of ET and to eventually devise more effective treatments.
References
Louis ED, McCreary M. How common is essential tremor? Update on the worldwide prevalence of essential tremor. Tremor Other Hyperkinet Mov 2021 Jul 9;11:28. doi: 10.5334/tohm.632. eCollection 2021.
Louis ED, Ottman R. How many people in the United States have essential tremor? Deriving a population estimate based on epidemiological data. Tremor Other Hyperkinet Mov 2014; 14; 4:259 doi: 10.7916/D8TT4P4B.
Benito-Leon J, Bermejo-Pareja F, Louis ED. Incidence of essential tremor in three elderly populations of central Spain. Neurology 2005;64:1721-1725.
Correspondence: Elan D. Louis, MD, MS, Department of Neurology, University of Texas Southwestern, 5323 Harry Hines Blvd, Dallas, TX, 75390-8813 USA. Email: elan.louis@UTSouthwestern.edu