Essential tremor (ET) is the most common movement disorder, with at least 200,000 new U.S. cases annually. While ET is not life-threatening, research has led to four new lines of thinking about ET.
1. A family of diseases
Doctors and researchers are backing off from a universal approach to ET. Differences in ET patterns exist, hinting that ET is not a single disorder. Some patients develop walking/balance difficulties that make falls a hazard, while others have tremors localized only to hands or neck. There are subgroups of patients whose eye movements become abnormal, or who develop cognitive dysfunction. Recent studies on deceased patients’ brains suggest the ET doesn’t always affect brains the same way. Thus, there may ET subcategories – or even distinct diseases. This may help explain why a drug works with one patient but not another. Work is ongoing to organize ET into diagnostic categories that could lead to more effective treatment matching.
2. Focusing on the cerebellum
A small area at the back of the brain is called the cerebellum (Latin for little brain). It is responsible for coordinating voluntary movement, posture, balance, and motor control. Cerebellum activity has “outflow pathways” that lead to the thalamus deep in the brain’s center. When the cerebellum or its outflow pathways are not functioning properly, the thalamus receives incorrect signals that it relays to the muscles, causing tremors. Surgical procedures (deep brain stimulation, thalamotomy) act upon the thalamus to block these erroneous signals from reaching the muscles.
3. ET as a neurodegenerative disorder
Once ET begins, it has a gradual progression toward worsening tremors and possible problems in other body areas. Cognitive/emotional difficulties may show up. As people age, severity can increase to a point where ET has a profound impact on independence and quality of life. ET is a process that takes a cumulative toll over time. Research is aimed at identifying risk factors that trigger cell death or the buildup of harmful proteins, in the hope of creating preventive therapies.
4. The role of GABA
Researchers have identified a particular chemical messenger called GABA that helps control motor movements by acting as a pacemaker. One aspect of ET as a neurodegenerative disorder appears to be the dying off of cells in the cerebellum that manufacture GABA. As GABA levels drop off, cerebellum activity goes into high gear, resulting in “hyperactive” messages to the thalamus.
Together, these four views of ET represent the most recent evolution in how doctors and scientists understand ET. The promise of a better life with ET, or eliminating it altogether, lies with them.