Comedian Jerry Lewis died in August, 2017. He was 91 years old, and the cause of death was identified as cardiovascular disease. Perhaps it’s not surprising, since at that age, many of the body’s systems are “rusting.” For many aging people, not just their bodies but also their minds begin to decline as they become elderly. Jerry Lewis himself observed, “When you’re 89, dementia develops. I mean, I’ve told a story onstage, and I’m telling it with a full heart, and I forgot the damn punch line.”
As the brain ages, the risk of cognitive impairment goes up. You’ve probably had an older relative remark on how forgetful they’re becoming: they can’t remember why they walked into the kitchen, they can’t find their glasses, they forgot a dentist appointment, etc. The condition of declining mental function is called dementia, and is characterized by memory problems, impaired reasoning and even personality changes.
Essential tremor and dementia risk in older adults
Essential tremor (ET) is the most common movement disorder. It can occur at any age, but is most associated with aging since the incidence increases as people grow older. Although the exact cause isn’t known, we know much about the two types of physical changes in the brain that are associated with ET: a reduced number of cells called Purkinje cells, and the formation of clustered proteins called Lewy bodies. Lewy bodies, in particular, are associated with other neurodegenerative disorders such as Alzheimer’s disease.
There is published evidence that in older adults with ET, the risk of dementia is greater than it is among same-age people who don’t have ET. For example, Benito-León et al. (2016) cite various studies that have found the following:
- Mild cognitive deficits, mainly in attention and frontal executive functions, verbal memory, and visuospatial processes have been reported in ET
- Cognitive deficits in ET might be not static and seem to progress at a faster rate than in normal older adults
- Individuals with late-onset ET (e.g., older adults) seem to have an increased prevalence of mild cognitive impairment and dementia, and a higher risk of incident dementia than those with earlier-onset ET.1
The other side of the coin
On the other hand, a research group out of the Banner Sun Health Research Institute (Sun City, AZ) challenges some of these conclusions. For one publication, Shill et al. (2014) used a large database generated by a long-term study on aging called the Arizona Study of Aging and Neurodegenerative Disorders (AZSAND) to explore patterns of ET and associated dementia.2 AZSAND includes over 3000 participants, which makes sense given the number of retirees living in and around Sun City. Beginning with baseline evaluations in 1997, each AZSAND subject has undergone annual follow-up assessments. For their analysis, the Shill team identified a total of 507 cases that met their criteria. Of the total cases, 83 had essential tremor and 424 did not. The average age for the tremor patients was 80 (give or take 5.9 years), and for normal individuals it was 76 (give or take 8.5 years). Among those with tremor, the average duration since it started was 5.2 years at the time they enrolled in the study. All participants had been followed for an average of 5.4 years. Thus, the team drew their conclusions from what they describe as “subjects with ET versus controls without tremor in a large, well-categorized cohort of individuals involved in a longitudinal aging study…”
Their position contrasts with prevailing theories about ET and dementia. They write, “The main finding of this study was that all subjects with ET did not develop dementia at a higher rate than control subjects without tremor in this well-categorized longitudinal study.” In fact, there are other papers by the Banner group that draw sharply different conclusions about Purkinje cells, Lewy bodies and other evidence among elderly people with ET.
What does it all mean?
There are so many gaps in our understanding of ET that a special body convened to identify areas where we lack knowledge and try to systematize the research that needs to be done. In May 2015, the National Institute of Neurological Disorders and Stroke, National Institutes of Health (USA) convened a group of international experts to recommend problematic topics and how research can be done and coordinated globally. This is just the beginning, but it is an optimistic sign of the determination and commitment behind understanding – and perhaps someday preventing or curing – this puzzling disorder.
Meanwhile, Sperling Neurology Associates offers a breakthrough treatment called MRI-guided Focused Ultrasound to control tremors. It is an outpatient, noninvasive and durable intervention. To learn more about this exciting new procedure, explore our website.
1 Julián Benito-León, J, Contador I, Louis E, Cosentino S, Bermejo-Pareja F. Education and risk of incident dementia during the premotor and motor phases of essential tremor (NEDICES). Medicine (Baltimore). 2016 Aug; 95(33): e4607.
2Shill HA, Hentz JG, Jacobson SA, Belden C et al. Essential tremor in the elderly and risk for dementia. J Neurodegener Dis. 2014;2014:328765.