Causes and Consequences of Benign Essential Tremor

Benign essential tremor is probably the most common of all movement disorders. Someone with essential tremor has increased shakiness, usually of the hands or arms, whenever the limb is being used. This distinguishes the tremor from that of classical Parkinson's disease, which is usually worse when the arm and hand are at rest.

What Does "Benign" and "Essential" Mean in Benign Essential Tremor?

The term "essential" is not meant to indicate the tremor's value. The shaking is an annoyance and can even be debilitating in some cases. The word "essential" is intended to indicate that tremor is the only symptom involved — that it's the "essence" of the entire problem. Similarly, the word "benign" signifies that the disorder, while annoying, is not inherently dangerous.

These views, while comforting and widely held, might be wrong.

For one thing, essential tremor is probably not actually just one disease, but rather a symptom caused by any one of a number of different processes. Some of these may indeed be "benign," but others may be more serious.

Diseases That Mimic Essential Tremor

To be diagnosed with essential tremor, one must first exclude known mimics. More serious problems such as multiple sclerosis, traumatic brain injury, tumors, vascular disease, Wilson's disease, atypical Parkinson's disease, drugs, toxins, and more can cause a tremor that worsens when the hand and arm are in use. If one of these things is found to be the cause of the tremor, the tremor is not considered "essential," but part of a more serious medical condition.

The controversy begins after we have excluded as many of those disorders as possible, and only the tremor seems to remain. Even then, there may be hints that the tremor is a sign of a wider, more involved process in the body.

Cognitive and Emotional Aspects of Essential Tremor

A growing number of scientists have described subtle differences in how people with essential tremor perform on neuropsychological tests. In one study, people with essential tremor performed worse than the control group on tests of memory, attention, and concentration.

In addition to these cognitive differences, people with essential tremor have been described as being at an increased risk for depression, as well as to suffer from anxiety or social phobias. Some studies have described patients with essential tremor as more introverted, rigid, or lonely than the general population. All of these characteristics, though, were described by comparing groups of people, meaning that there is still a lot of variation between individuals.

Brain Changes in Essential Tremor

Neuropathologists have studied the brains of people with essential tremor after their death. The results are suggestive but conflicting. Some people have described changes in the cerebellum, a region of the brain commonly associated with movement and coordination. Furthermore, some studies have described a higher chance of finding Lewy bodies, usually considered to be a sign of Parkinson's disease, in part of the brainstem known as the locus coeruleus.

Some pathologists believe that these are signs that essential tremor may be a neurodegenerative illness along the lines of Parkinson's disease or Alzheimer's disease. Other studies have found that people with essential tremor may be at an increased risk of developing Parkinson's disease, Alzheimer's disease, and progressive supranuclear palsy. Perhaps there is a common predisposition towards neurodegeneration that links tremor with these other disorders.

On the other hand, others state that the increased risk of developing other diseases may be simple misdiagnosis — meaning that perhaps some people who initially were said to have essential tremor had an unusual presentation of Parkinson's or another known movement disorder. These researchers believe that there is no current need to call essential tremor degenerative itself.

The Role of the Cerebellum in Essential Tremor

Certainly, many studies have suggested that the cerebellum does not function normally in essential tremor. This may explain why some people with essential tremor have other "cerebellar findings" on their neurological examination, such as ataxia or poor hand-eye coordination.

In the last decade, we have become increasingly aware that the cerebellum does more than coordinate movement — it may help to coordinate thoughts and perhaps emotions as well. Studies have connected cerebellar activity with the dorsolateral prefrontal cortex, a region of the brain classically associated with problem-solving, attention, and memory.

What Does This Mean for Me If I Have Essential Tremor?

There is compelling evidence that cognition differs between people with and without an essential tremor. Those differences, however, are slight, and the cause of those changes is unclear. If essential tremor is, in fact, a degenerative illness, it's very slow. How this all relates, if at all, to patient care is unclear at this time. Perhaps identifying more serious causes of essential tremor could end up benefiting people who would otherwise be written off as having an entirely benign disorder.