Essential tremor (ET) is often misdiagnosed as Parkinson’s disease (PD). Either one is scary, since both have no known cause or cure. Also, both ET and PD are progressive, meaning future deterioration is expected. While ET does not have the same devastating consequences at PD, it occurs eight times more often. One might think, then, that people would be that much more aware of ET. Yet the opposite is true. Far more research and funding are devoted to PD, and ET remains in the shadows.
Can ET and PD occur together?
Even more frightening is when PD or other parkinsonism syndrome occurs along with ET. “Parkinsonism” refers to conditions that resemble PD in many ways but are not true PD. A big difference is that medications that work for PD, such as L-dopa, have little or no effect on parkinsonism. In addition, a person with parkinsonism may not have tremors but will have other similar PD symptoms: bradykinesia (slow movement), stooped posture, stiff walking, small steps, and reduced arm swinging when walking. Treatment using Deep Brain Stimulation (DBS) does not help with parkinsonism.
There are other variants that are considered atypical Parkinson’s disease (APD). There is also a very rare condition called Progressive Supranuclear Palsy (PSP). In its early stages it also looks like PD or one of the forms of parkinsonism but with ongoing degeneration, stiffness, dizziness and falls become worse. There can also be personality and cognitive changes. Since any of the above can co-occur with ET, gaining an accurate diagnosis of co-existing conditions can be a confusing process. Symptoms overlap, so trying to tease out one diagnosis from another is challenging.
One Canadian study
How often does PD or parkinsonism exist alongside ET? No one knows for sure. A 2019 Canadian studyi out of the University of Saskatchewan and the Saskatchewan Health Authority examined this question. The findings were based on case records over a 50-year period at a single medical center. Twenty-one patients were identified who had been diagnosed with ET and subsequently also diagnosed with PD or parkinsonism. The authors note, “The diagnosis of parkinsonism was made when bradykinesia [slow movement], rigidity, and resting tremor were all clinically evident.” Keep in mind that a hallmark of ET is action tremor or intentional tremor (tremors begin when the affected body part begins to act), although some people with ET report that their tremors occur even when at rest. However, for this study, the presence of resting tremors was considered a symptom of a separate condition from ET.
The researchers found that all common variants of parkinsonism could exist with ET. They report that PD was the most common co-existing condition, affecting 67% (about 2/3) of cases. The next most common was the rare condition known as PSP. Thus, they concluded, “In most essential tremor/Parkinson’s syndrome patients, the main motor features of parkinsonism-bradykinesia, rigidity, and resting tremor were identifiable.”
Controversy about the relationship between ET and parkinsonism
There is no doubt that some people with ET go on to eventually develop PD or other parkinsonism syndrome. Since there continue to be “…unresolved questions about the link between the two disorders including lack of verifiable diagnostic criteria for the two disorders and marked overlap in phenomenology,”ii why this occurs and what the specific brain abnormalities might be is not understood. Reports in the literature identify such features as
- Overlapping motor and cognitive symptoms
- Rapid eye movement sleep behavior disorder in 26-43% of those with ET
- Prevalence of those with longstanding ET later being diagnosed with PD
- Greater prevalence of ET in family members of PD patients
- The presence of Lewy bodies in the brains of 15-24% of people with ET.iii
Recommendation for those with ET
ET, PD and parkinsonism have one thing in common: they don’t affect individuals in identical ways. There are accepted diagnostic guidelines, but an infinite number of small or large differences can occur: rate of progression, response to medication, nature of lifestyle problems and impairment, etc. If two persons with ET were to compare notes, they would quickly find that things like propranolol helps one but not the other, or one of them gets terrible restless leg syndrome at night while the other has never had it, etc. Thus, there is a growing theory that ET is not a single disorder, but a group of disorders.
For those with ET who notice that they have additional symptoms that don’t fit the “classic” ET descriptions in books or websites, we recommend discussing the situation with a movement disorder specialist. Perhaps there’s no cause for concern, but it may be worth seeking an evaluation to rule out a co-occurring form of parkinsonism. Accurate information may be your best friend, since it both equips you and your doctor to strategize treatment, and also to manage anxiety and gain peace of mind.
iRajput AH, Rajput EF, Bocking SM, Auer RN, Rajput A. Parkinsonism in essential tremor cases: A clinicopathological study. Mov Disord. 2019 Jun 10. https://www.ncbi.nlm.nih.gov/pubmed/31180613
iiTarakad A, Jankovic J. Essential tremor and Parkinson’s disease: exploring the relationship. Tremor Other Hyperkinet Mov. 2018;8:589.