Parkinson's disease is much less common than Essential Tremor, and it presents itself in markedly different ways; however, there are similarities. While treatments overlap in some areas, receiving the best care requires an accurate diagnosis. The two conditions have key differences to look for:
     
Below are some of the differences & resemblances between the two diseases: 
 
Essential Tremor
  • Affects hands, head, and voice,
  • Onset can occur at any age,
  • Family history in >50% of patients.
  • Action tremor. However, rest tremor has been reported with more severe disease and longer disease duration in various studies.
  • Usually affects both sides of the body, but commonly starts in one hand
  • Jaw Tremor may occur; jaw tremor in ET is more typically a postural or kinetic tremor rather than a rest tremor.
  • Alcohol often improves tremor
 
Parkinson’s
  • Affects hands and legs, but rarely the head and voice.
  • Onset generally around 60.
  • Rarely family history.
  • Resting tremor. However, postural tremor has been reported in patients with PD, especially young patients.
  • Tremors usually start on one side of the body, commonly in the hands, and progress to the other side.
  • Jaw tremor may occur
  • No effect on consumption of alcohol


(1) Resting tremor occurs when the muscle is relaxed, such as when the hands are resting on the lap. With this disorder, a person’s hands, arms, or legs may shake even when they are at rest. Often, the tremor only affects the hand or fingers. This type of tremor is often seen in people with Parkinson’s disease and is called a “pillrolling” tremor because the circular finger and hand movements resemble rolling of small objects or pills in the hand.  
Action tremor occurs with the voluntary movement of a muscle. Most types of tremor are considered action tremor. There are several sub-classifications of action tremor, many of which overlap.
  • Postural tremor occurs when a person maintains a position against gravity, such as holding the arms outstretched.
  • Kinetic tremor is associated with any voluntary movement, such as moving the wrists up and down or closing and opening the eyes.
  • Intention tremor is produced with purposeful movement toward a target, such as lifting a finger to touch the nose.  Typically the tremor will become worse as an individual gets closer to their target.
  • Task-specific tremor only appears when performing highly-skilled, goal-oriented tasks such as handwriting or speaking.
  • Isometric tremor occurs during a voluntary muscle contraction that is not accompanied by any movement such as holding a heavy book or a dumbbell in the same position.


​https://www.ninds.nih.gov/health-information/disorders/tremor
What is Parkinson's
PD is a neurodegenerative disease. It occurs when certain nerve cells, or neurons, die or become impaired. This degeneration takes place in an area of the brain called the substantia nigra, located in the brainstem, which is one of the centers that control movement (also called the basal ganglia). Normally, these neurons produce a chemical known as dopamine, which is responsible for transmitting signals across the nerve pathways to produce smooth, purposeful movements. Loss of dopamine causes nerve cells to fire abnormally. This leaves people living with PD with difficulty directing or controlling their movements in a natural manner. People living with PD have usually lost 80% or more of dopamine-producing cells in the substantia nigra by the time symptoms are visually apparent. In addition, there is also neuronal cell loss and related pathology in other brain regions, responsible for other non-motor symptoms.

The main reason why these cells die or become impaired is still a mystery. Most scientists believe that both genetic and environmental factors are contributing causes. However, how they lead to PD is still unclear.
Diann Shaddox Foundation for Essential Tremor