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Parkinson's disease and Essential Tremor are both movement disorders that cause tremor, but there are also some extremely significant differences between the two conditions.

Tremors — involuntary shaking or twitching movements that can strike the hands, arms, feet, legs, face, and sometimes other parts of the body — have got to be the most well-known and characteristic symptoms of Parkinson's disease. Parkinson's-related tremors nearly always begin on one side of the body, and patients will notice them when they're not engaged in any particular activity, at rest. 

Anyone who has noticed this kind of shaking or twitching is likely to start worrying they could have Parkinson's disease, whether they Google their symptoms or just pull the knowledge that Parkinson's disease causes tremors from their mind.

It is important, however, to keep in mind that:

  • Not all Parkinson's patients experience tremors — up to a quarter never have them, in fact. 
  • Not all people with a tremor suffer from Parkinson's disease. 

Essential Tremor is another neurological condition and movement disorder that leads to tremor, and it's actually much more common than Parkinson's. While tremor is the defining symptom of Essential Tremor, Parkinson's disease is also marked by slowness of movement, balance problems, rigidity, and issues with gait. (To make the diagnostic process even more confusing, a person can have both these conditions.)

What do you need to know about the differences between Parkinson's disease and Essential Tremor?

Parkinson's vs Essential Tremor: The timing of the tremor

Parkinson's patients most commonly experience tremors when they're "at rest", meaning they're not currently doing anything else with the part of the body in question. The tremor will come to an end when you start doing something else with your hand, leg, or wherever else the tremor is — like simply moving it. 

People with Essential Tremor, meanwhile, primarily experience tremors when they are active and moving — these are called action tremors. Somewhere between 20 and 30 percent of people with Essential Tremor also do experience rest tremors, however, so having those doesn't necessarily mean you have Parkinson's. Where ET patients do have rest tremors, they're more likely to strike the arm. This isn't true for people living with Parkinson's disease, who can have rest tremors in varied body parts.

Parkinson's disease vs Essential Tremor: How often do the tremors come along, and how bad are they?

People with Essential Tremor typically experience a higher tremor "frequency" than those with Parkinson's disease — their tremor shows up more often and sticks around for a longer period of time.

The strength (also called amplitude or magnitude) of the tremors seen in Essential Tremor are also more variable, ranging from "barely there" to "is my body experiencing an earthquake?". Parkinson's disease patients, on the other hand, are more likely to experience much stronger tremors that come along less frequently. 

A closer look at your family history

The majority of cases of Parkinson's disease do not seem to run in families — depending on the data set you look at, anywhere from less than 10 percent to up to 20 percent of people with Parkinson's have (or had) a close relative with the disease. In contrast, over half of people diagnosed with Essential Tremor have other known cases of the same condition somewhere within their more immediate families. Your family history may, thus, give you a clue as to what condition you are more likely to suffer from. This is of course one of the reasons your diagnosing doctor will inquire about your family history.

What side of the body is affected by tremors?

Parkinson's-related tremor is well-known to typically initially manifest itself on only one side of the body. It will often go on to affect both sides only later on, as the disease enters its later stages, but one side of the body will still remain disproportionally prone to tremor. People with Essential Tremor, on the other hand, tend to have "symmetrical" or "bilateral" (meaning both sides) tremors from the very start. 

Where does your tremor occur?

The tremors associated with Essential Tremor are most likely to affect the hands and lower arms, but other parts of the body may also experience tremors — the torso, neck, face, and even tongue. Legs, meanwhile, will mostly be "spared". Parkinson's disease is different. Although the hands are also the most frequently affected body part, tremors occur in the legs quite commonly, while the head and face almost always remain unaffected. 

Your age

Parkinson's disease is well known to mostly occur in people over 60, with those over 85 being at a much higher risk still — only a small minority of patients are diagnosed before age 50, in which case it's considered "early onset" Parkinson's disease. Essential Tremor is most likely to show up during middle age, but it is much more likely than Parkinson's to affect younger people. 

Handwriting: A strange clue

Micrographia, very small and crowded handwriting, is one of the hallmark signs of Parkinson's disease that doctors will look for — it's even one of the main reasons they'll ask patients to fill diagnostic questionnaires out themselves. This handwriting may start off having a normal "font size", but then gradually become smaller and smaller as the patient writes more. 

People with Essential Tremor don't have micrographia — their handwriting can be affected by their condition, but it's much more likely to become larger and more shaky (unsurprisingly, since tremor usually shows up while active). 

What resolves your tremor?

The tremors seen in Parkinson's disease almost always get better when they start using the medication levodopa — along with their other motor symptoms, like slowness of movement and rigidity. The same medication doesn't work well for people with Essential Tremor, who instead benefit from treatment with primidone and propranolol. Essential Tremor patients may also notice that drinking alcohol stops or reduces their tremor, which is not the case in those who have Parkinson's disease.

Parkinson's disease vs Essential tremor: The diagnostic process

Despite all these differences, Parkinson's disease and Essential Tremor do share some common features — both are movement disorders, both feature tremor, and tremors will be worsened by stress in people with both conditions. Because the right treatment depends on the right diagnosis, it is important that diagnosing doctors make the distinction between Parkinson's and Essential Tremor. 

Besides:

  • Patient reports on their symptoms
  • Diagnostic checklists 
  • Physical examinations of various kinds, such as being asked to complete certain activities
  • A look at your family history

Your doctor may also:

  • Order a dopamine transporter imaging test — Parkinson's disease patients gradually lose dopamine, so test results indicative of this suggest Parkinson's disease.
  • Use techniques such as accelerometry to look at the severity and patterns of your tremors. 
  • Test your sense of smell, something that is often affected in people with Parkinson's disease.

  • Fekete R, Jankovic J. Revisiting the relationship between essential tremor and Parkinson’s disease. Mov Disord 2011,26:391-398.
  • Photo courtesy of SteadyHealth.com

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