Differences between Parkinson’s and Essential Tremor

What is Tremor?

Tremor is the involuntary or unintentional rhythmic movement of one or more parts of the body and it may involve the hands, arms, legs, face, head, trunk, or vocal cords. It may be caused by a number of factors such as neurological disorders due to various causes with Parkinson’s disease being one of them as well as certain drugs, alcohol abuse or withdrawal, mercury poisoning, hyperthyroidism, or liver failure. Certain types of tremors may be inherited and are seen to run in families, but for which no known cause can be found, and these are called essential tremors.

Types of Tremor

Tremors may be classified clinically into :

  • Rest tremor occurs in a body part that is supported while lying in bed or seated.
  • Action tremor which comprises of :
  1. Postural tremor occurs when trying to hold up a body part against the force of gravity such as when extending the arms horizontally, sitting up straight without support, pointing with fingers, or sticking out the tongue.
  2. Kinetic tremor occurs during a voluntary movement such as in nose-finger-nose testing, heel-knee-shin testing, drinking from a cup, writing, eating and so on.

Characteristics of an Essential Tremor

  • An essential tremor is an action tremor, where there is a combination of postural and kinetic tremor in various degrees. The patient may have problems such as difficulty in holding a glass without spilling, shaving, or eating but there is no tremor on rest.
  • Genetic factors play an important role in essential tremor and is inherited as an autosomal dominant gene.
  • Essential tremor is bilateral and the hands are almost always affected, along with the face, head or trunk. Lower extremities are rarely affected.
  • Absence of neurological signs.
  • Isolated head tremor without problems in posture.
  • Absence of features of Parkinson’s disease associated with bradykinesia (slow movements) and rigidity.
  • Cause of essential tremor is not known.
  • Medicines responds well to primidone and beta-adrenergic blockers such as propranolol but does not respond to anti-Parkinson medications.

Characteristics of a Parkinson’s Tremor

  • A Parkinson’s tremor is observed at rest and there is a typical pill-rolling type of tremor with rolling of thumb over forefinger. The tremor disappears during sleep or may improve during intentional movements.
  • No strong genetic factors have been identified in Parkinson’s disease although research in this field is still ongoing.
  • In the initial stages, the Parkinson’s tremor is unilateral, starting on one side of the body, but may become generalized in the later stages.
  • Other neurological signs related to Parkinson’s disease may be present.
  • Absence of a head tremor but postural instability present.
  • Parkinson’s tremor is associated with bradykinesia and rigidity, leading to typical features of Parkinson’s disease such as slow shuffling gait, reduced arm swing and shortened stride.
  • Parkinson’s disease is a degenerative disease of the brain with symptoms caused by a decreased production of dopamine,  resulting in characteristic features of Parkinsonism such as tremor, rigidity, bradykinesia and postural instability.
  • Anti-Parkinson’s medicines assists with reducing the symptoms of Parkinson’s disease which is not evident in essential tremors.

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