There May Be More Essential Tremor Cases Than We Know

I have previously written about recent insights that essential tremor (ET) is not a single neurological dysfunction but more likely a group of disorders. In some respects, this is both good news and bad news. The good news is that this theory helps validate that pharmaceuticals may help some individuals but not others. The bad news is that it makes finding a cure or prevention strategy more challenging.

Another challenge is knowing exactly how many people are affected by ET. One of the confounding factors is that ET is not always accurately diagnosed. It is often mistaken for Parkinson’s disease (PD) or other conditions. Another factor is that people with mild ET, especially those with a family history, may tolerate it as a fact of life and not seek medical help unless it becomes disabling.

How widespread is ET?

How prevalent is ET? Estimates on the number of cases vary, or are reported in different ways. According to International Essential Tremor Foundation, there are 10 million Americans with ET. An eMedicine article from Medscape tells us how uncertain estimates can be, with a range of 0.3-5.6% in the general population. To translate those percentages into real numbers, that would mean that for every million people, there would be anywhere from 3,000 to 56,000 cases. So you can see that pinning down an exact number is very difficult.

A paper published in July, 2018 suggests that more persons have ET than previously imagined.i The study by Louis, et al. is interesting because it involved not only 241 first-degree relatives of ET cases but also 77 non-ET spouses who served as normal controls for the study. All those enrolled in the study underwent a videotaped neurological examination and gave a detailed tremor history. Of particular note is that none of them, including the first-degree relatives, reported that they experienced tremor or had a prior diagnosis of ET. Furthermore, for each of them there was no significant tremor on screening spirals. So the initial impression was an absence of tremor in the study population.
More prevalent than expected
However, closer examination by specialists proved otherwise. The authors write, “All videotaped examinations were initially reviewed by a movement disorder neurologist blinded to subject type, and among those with head tremor on examination, co-reviewed by two additional movement disorders neurologists.” What they found is surprising.

Out of the 241 first-degree relatives, 26 (10.8%) had isolated, transient head tremor compared with 2 (2.6%) of the spousal controls. None of the relatives or controls had “significant upper extremity tremor and none met inclusion criteria for ET based on the presence of upper extremity tremor… It was always transient (generally a single back and forth wobble) and rare (observed briefly on one or two occasions during the videotaped examination…” The “wobbles” were characterized as tremors based on the frequency, amplitude and quality of the movement which ruled them out as voluntary head motions.

The authors did not offer a clinical explanation for the basis of such head tremor, but hypothesize that in families with ET it could be an early feature. “Indeed, one-in-ten otherwise unaffected first-degree relatives of ET cases exhibited such tremor. To a far lesser extent it was also observed in ‘unaffected’ controls.”

They concluded that ET may have a greater degree of prevalence than previously suspected.

Hope for ET control

When tremors are mild, they can be inconvenient, annoying and occasionally embarrassing or even humiliating, especially if they are present during childhood and adolescence when age-mates can be unwittingly cruel. However, as tremors progress, tremors become obstacles that make ordinary acts of daily living nearly impossible. Medications such as primidone and propranolol only help about half of people, and eventually even those lose effectiveness – or cause undesirable side effects at higher doses.

Sperling Neurosurgery Associates offers MRI-guided Focused Ultrasound (MRgFUS) to control hand tremors. MRgFUS is a noninvasive, outpatient alternative to Deep Brain Stimulation, which is a major neurosurgery involving holes through the skull to place electrodes in the brain. MRgFUS is safe, effective and durable, with minimal-to-no side effect risks.

For more information or a consultation, contact Sperling Neurosurgery Associates.

iLouis ED, Meyers JH, Cristal AD, Patel A et al.Transient, Isolated Head Tremor in “Unaffected” Individuals: Is Essential Tremor an Even More Prevalent Disease Than We Suppose? Front Neurol. 2018 Jul 13;9:570.

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