# A Study on the Essential and Parkinson's Arm Tremor Classification +
## 2 Essential and Parkinson's Tremor  
### Essential Tremor: Overview and Diagnosis  
Essential tremor (ET) is described as a disorder of the nervous system in which the hands and arms are usually trembling [37]. Individuals over 40 years of age who are diagnosed with essential tremor belong to 4% of the world's population [38]. Some of them manifest tremor only in certain postures (static shaking), while others present it when performing a task, for example during writing or eating (motor shaking). Most patients with ET experience both shaking forms, while voluntary movements, such as holding a fork, usually worsen the tremor. This contrasts with [PERSON]'s disease, in which the tremor tends to diminish with such movements. While the Parkinsonian tremor maximizes at rest with respect to amplitude and frequency [39], the essential tremor's higher frequency and amplitude occur mainly during activity and are decreased at rest [40]. However, these changes in the tremor amplitude and frequency cannot be easily determined and depend each time on the affected person and on the condition stage. The causes of ET are various genetic mutations, which are not yet fully determined, and it is often observed that ET patients have difficulty in daily activities, such as writing, swallowing food, speaking, etc. [41]. Before someone is diagnosed with ET, other factors must first be excluded, such as:  
* chronic alcohol use;
* intake of antiarrhythmic, antidepressant and antispasmodic drugs;
* use of substances such as nicotine or cocaine.  
Tremor can additionally be caused by thyroid problems, strokes and [PERSON]'s disease. It is not uncommon for Parkinson's Tremor (PT) to be mistaken for ET. Initially, ET usually affects the hands, head and voice, while the tremor that characterizes PT occurs primarily in the hands and then spreads to the jaw, legs and other parts of the body. It is also important to note that ET does not cause any other health problems, unlike [PERSON]'s disease that causes problems in posture, movement and gait. Finally, as it was previously stated, ET occurs mainly during movement and not in a resting position such as [PERSON]'s disease.  
ET has some clinical traits that facilitate its diagnosis, namely that the tremor:  
* Starts gradually, mainly on one side of the body and focusing on the hands.
* Gets worse as movement increases.
* Increases with caffeine intake, stress, excessive fatigue and abrupt temperature changes.
* Causes a \"yes-yes\" and \"no-no\" head movement.  
In addition to the ET symptoms mentioned above, as with PT, there is a scale of tremor evaluation called The Essential Tremor Rating Assessment Scale (TETRAS) [42], presented in Table 1. TETRAS evaluates the tremor in the head, the language, the face, the voice, along with the upper and lower limbs. Furthermore, TETRAS rates the tremor by evaluating the performance during the conduction of daily activities, such as writing. Depending on the performance of the examined person, tremor is scored 0 to 4 points, with 0 marking absence of tremor. The length numbers (e.g., 1-3 cm) indicate the peak oscillation amplitude of the body part under evaluation.