Essential tremor is a nerve disorder in which tremors (shakes) occur in a person who is moving or trying to move and no cause can be identified.

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.

Essential tremor is the most common form of abnormal tremor. Although the cause is unknown, new research shows that the part of the brain called the cerebellum does not appear to work correctly in patients with essential tremor. The cerebellum is the part of the brain that coordinates muscle movements.

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 make the tremors go away completely. People with essential tremors may have trouble holding or using small objects, such as silverware or a pen.

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.

There are several different types of essential tremor, including young-onset essential tremor and 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 genes may play a role in the development of essential tremors. Not only have the tremors been shown to be passed down through families, but 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 also play a role.

Essential tremors can occur at any age but are most common in people older than 65.

The tremors:

• 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 laboratory test to diagnose 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 be done to rule out other causes of tremors, such as excessive caffeine or tobacco use, alcohol withdrawal, use of certain medications (for example, asthma drugs, lithium, certain antidepressants and anti-seizure drugs), hyperthyroidism, pheochromocytoma, and Wilson's disease.

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.

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

Medications help relieve symptoms in most patients. Two medications are considered the first line of therapy: propranolol and primidone. Propranolol blocks the action of stimulating substances called neurotransmitters, particularly those related to adrenaline. Primidone is an anti-seizure medication, which also control the function of some neurotransmitters. The drugs can have significant side effects.

Side effects of propranolol include:

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

Side effects of 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, topiramate, mild tranquilizers such as alprazolam or clonazepam, and calcium-channel blockers (flunarizine and nimodipine).

Botox injections, given in the hand, have been used to reduce tremors by weakening local muscles.

In severe cases, surgery may be an option. 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 decrease tremors but can lead to alcohol dependence if used in excess. How alcohol decreases an essential tremor is unknown.

An essential tremor is not a dangerous condition, but it may be annoying and embarrassing.

If it is severe, essential tremor can mildly interfere with activities, especially fine motor skills such as writing. Speech is occasionally involved. Medications can cause side effects.

Call for an appointment with your health care provider if essential tremor is interfering with ability to perform daily activities.

Call your health care provider if side effects of medications occur, including fainting, very slow heart rate, confusion or changes in alertness, lack of coordination, problems walking, and prolonged nausea/vomiting.

Techniques to reduce emotional stress, such as counseling and exercise, may help. Stress can make essential tremors worse.