Essential tremor is a nerve disorder in which tremors (shakes) occur without an identifiable cause when a person is moving or trying to move.

All people have some degree of tremor during movement. This shaking normally involves mainly the hands. Stress, fatigue, anger, fear, caffeine, and cigarettes may temporarily worsen this type of tremor to the point that it becomes visible to the naked eye.

Essential tremor is the most common form of abnormal tremor. It resembles an exaggerated shaking. Essential tremor is worsened by the same factors that enhance normal tremors. Although the cause is unknown, new research shows that one part of the brain, called the cerebellum, does not appear to function properly in patients with essential tremor.

The cerebellum is the part of the brain that coordinates muscle movements and provides accuracy and harmony to voluntary movement. Nevertheless, no brain lesions have been identified in patients with this form of tremor.

There is evidence of several different types of essential tremor (such as young-onset essential tremor or essential tremor with head tremor). These types differ in their response to treatment.

If an essential tremor occurs in more than one member of a family, it is called a familial tremor. It appears that essential tremor has some genetic basis, not only because of the hereditary pattern observed in some families, but also because an identical twin (who shares the same genes) of a person with essential tremor is twice as likely as a fraternal twin (who has different genes) to have essential tremor.

Since some identical twins do not share this condition, environmental factors must play a role as well. Essential tremors can occur at any age but are most common in people older than 65.

Essential tremor is a relatively benign condition, affecting movement or voice quality, but with no other effects. It involves a rhythmic, moderately rapid tremor of voluntary muscles. Purposeful movements may make the tremors worse, while avoiding hand movements may suppress the tremors completely. There may be difficulty holding or using small objects (such as silverware or writing utensils).

Over time, the tremors may affect the hands, arms, head, voice box, eyelids, or other muscles. An essential tremor rarely involves the legs or feet. It may start in one body part but can progress to include other parts.

• May be occasional (sporadic), temporary (episodic) or occurring at intervals (intermittent)
• Occur at a rate of about 6 to 10 oscillations per second
• May affect the head, hands, arms, eyelids, voice
• Less commonly affect the legs and feet
• May not affect both sides of the body equally
• Worsen with voluntary movement or emotional stress
• Disappear during sleep
• Typically improve with alcohol

There is no diagnostic laboratory test for essential tremor. The diagnosis is based on the patient's history, a physical examination revealing tremor on voluntary movement, and no other abnormalities.

However, some testing may rule out other causes of tremors, such as excessive caffeine or tobacco use, alcohol withdrawal, use of certain medications (some asthma drugs, some antidepressants, lithium, some anti-seizure drugs), hyperthyroidism, pheochromocytoma, Wilson's disease (a rare condition in which copper accumulates in the brain and liver), and other disorders.

Routine laboratory tests and brain imaging studies (such as CT scan of the head, brain MRI, and X-rays), or other tests are usually normal and not routinely performed.

Treatment may not be necessary unless tremors interfere with the patient's ability to perform daily activities or if they are considered embarrassing to the patient.

Medications result in symptom improvement in most patients, although one out of four patients may not benefit from treatment. Two medications are considered the first line of therapy: propranolol and primidone. Propranolol blocks the action of stimulant substances called neurotransmitters, particularly compounds related to adrenaline. Primidone is an anti-seizure medication, which also modulates the function of some neurotransmitters. Both medications are considered equally efficacious.

However, both have significant side effects. The side effects of propanolol include:

• Fatigue
• Shortness of breath (people with asthma should not use this drug)
• Slowing of the heart rhythm
• Nose stuffiness

The problems associated with primidone include:

• Drowsiness
• Difficulty concentrating
• Nausea
• Poor gait (walking style), balance, and coordination

Other medications that may reduce tremors include anti-seizure drugs such as gabapentin, mild tranquilizers such as alprazolam or clonazepam, and calcium-channel blockers (flunarizine and nimodipine).

Recently, intramuscular injections of botulinum toxin in the hand have been used to reduce tremor by weakening local muscles. If tremor is severe and interfering with functioning, surgery may also be an option to alleviate the tremor. Such surgery usually involves implanting a device called deep brain stimulator in a specific area of the brain called the basal ganglia.

Caffeine, found in substances such as coffee and soda, and other stimulants should be avoided.

Alcoholic beverages in small quantities may markedly decrease tremors but can lead to alcohol dependence if used in excess. The mechanism by which alcohol decreases an essential tremor is unknown.