NOTE: The following is not intended as an endorsement or recommendation of any product.
Describing essential tremor (ET) is either objective or subjective. What’s the difference? Well, objective means based in fact, so it’s able to be measured or quantified. Subjective means more open to interpretation, often based on experience, emotion or perception that will differ from one person to another. ET can be objectively quantified by measuring frequency (how many cycles in a given time period) and amplitude (how big or wide is the tremor from one “side” to the other).
When an ET patient first visits a doctor about the tremor – usually a specialist called a neurologist – the doctor wants to observe the tremor and also hear how the patient evaluates it. Most patients have no comparative basis for “measuring” their tremor in relation to someone else’s tremor, so they don’t usually have an objective sense of how bad it is or could become. Is it slight? Is it pronounced? One way to measure it is by how much it interferes with daily activities. Can the patient button buttons, eat soup without splashing it off the spoon, pick up a glass of water without spilling it? From the doctor’s perspective, “Understanding the patient vantage point is valuable as it is the starting point of personalized medicine.”i The patient’s initial self-assessment becomes an important baseline for evaluating how well treatment is working, since no two patients respond alike.
However, it is just as valuable to have an objective measure. Studies show that how patients evaluate their own tremor and how it is physically measured usually correlate well, but patients can miss subtle changes that indicate the tremor is getting worse. Thus, it can be helpful for the doctor to be able to put quantifiable facts in the clinical notes.
The most common measurement of ET is an internationally recognized unit called hertz (Hz). A single Hz means one cycle per second. It is named for Heinrich Hertz, “the first person to provide conclusive proof of the existence of electromagnetic waves…”ii Hz is used to quantify things like musical tones, radio waves, and the speeds at which electronics are driven. An important aspect of Hz is that it can be objectively measured using an electronic device. In ET, the range of Hz is from 2.5 Hz to 12 Hz, with the majority of cases averaging 5 – 5.7 Hz. Amplitude (the “size” of the tremor’s motion) can also be measured, but less reliably because of very small variations at any given time. The devices that are used are called transducers. “Transducers provide measurements of tremor amplitude that are objective, precise, and valid,” with amplitude being the most difficult to accurately calibrate.iii In ET cases, the higher the Hz (more cycles per second) the lower the amplitude; conversely, the lower the Hz (fewer cycles per second) the greater the amplitude or range of motion. Over time, as Hz becomes lower, the tremor becomes quite pronounced from side to side, making even simple tasks and normal appearance virtually hopeless. It might be said that when ET becomes advanced, there is little point in trying tomeasure it objectively (unless part of a research study) since the pronounced tremor is obvious.
There are three types of portable devices that can be used to quantify the severity of tremors. Each type registers a different function of motion. Translational motion includes forward/backward, side/side, up/down; rotational motion around a point includes roll, pitch or yaw. Measuring devices are useful for tracking tremor progression over time, since even small changes can be picked up electronically before the patient may experience them:
- Accelerometers – measure translational motion
- Gyroscopes – measure rotational motion
- Digitizing tablets – assesses quantitative motion of tremors visible to the unaided eye through tasks such as drawing or writing.
Today, it’s possible to use an app on a handheld device such as an Android™ phone in order to turn it into an accelerometer and/or gyroscope. According to a research team from Carnegie Mellon’s CyLab, “Measuring hand tremor on a mobile device has the potential to help those with hand tremor track and gain greater understanding of the tremor’s HARDWARE manifestation over time and help doctors make more informed diagnoses.”iv In addition, adapting the medication protocol for ET patients may become more efficient as the response time with mobile tracking will be very rapid.
Use of a portable measuring/monitoring device for ET is something that a patient and doctor should discuss, and together make an informed decision about. Will it have merit for this particular patient? Is it affordable? What’s the plan if ET appears to be progressing? Many patients may have no interest in the potential time consumption and psychological stress of monitoring, so it’s not for everyone.
While about 50% of ET patients respond well to medication, the other half get no benefit or the side effects are bothersome. For ET cases that seriously diminish quality of life and are not responsive to drugs, the Sperling Medical Group offers MR-guided Focused Ultrasound (MRgFUS) for the noninvasive treatment of tremors. For more information, contact the Sperling Medical Group.
iGutierrez J, Park J, Badejo O, Louis E. Worse and worse and worse: essential tremor patients’ longitudinal perspectives on their condition Front Neurol. 2016;7:175.
iiiElble R, McNames J. Using portable transducers to measure tremor severity. Tremor Other Hyperkinet Mov (NY). 2016;6:375.
ivDayton W, Collins P, Smith M, Selker T. “Measuring Hand Tremor with a Mobile Device. https://www.cmu.edu/silicon-valley/research/tech-showcase/pdfs/2010/HandTremor.pdf