Tremor is the unintentional, rhythmic muscle movement of one or more parts of the body. Most tremors occur in the hands, although they can also affect the arms, head, face, vocal cords, trunk, and legs. Sometimes tremor is a symptom of another neurological disorder, but the most common form occurs in otherwise healthy people. Some forms of tremor are inherited and run in families, while others have no known cause. Excessive alcohol consumption or alcohol withdrawal can kill certain nerve cells, resulting in tremor, especially in the hands. Other causes include an overactive thyroid gland and the use of certain drugs. Tremor may occur at any age but is most common in middle-aged and older persons.
- Essential tremor (sometimes called benign essential tremor) is the most common of the more than 20 types of tremor. The hands are most often affected but the head, voice, tongue, legs, and trunk may also be involved. Onset is most common after age 40, although symptoms can appear at any age.
- Parkinsonian tremor is caused by damage to structures within the brain that control movement. This tremor is associated with Parkinson disease. Parkinsonian tremor is a tremor at rest; the legs and face are frequently involved
- Dystonic tremor occurs in individuals of all ages who are affected by dystonia, a movement disorder in which sustained involuntary muscle contractions cause twisting motions or painful postures or positions.
- Cerebellar tremor is associated with damage to the cerebellum of the brain. Causes may include multiple sclerosis (most common cause) as well as tumors and strokes.
- Orthostatic tremor occurs when a patient is standing and often goes away when he or she is seated.
- Psychogenic tremor results from physical exhaustion, hypoglycemia, hyperthyroidism, heavy metal poisoning, stimulants, alcohol withdrawal or fever can occur in any muscle group. This type of tremor is often reversible and does not cause long-term problems.
Signs and Symptoms
- Essential tremor usually occurs when the muscles are opposing gravity, such as when the hands are extended, and worsens with movement. This type of tremor is usually not evident at rest. In addition to the hands and arms, muscles of the trunk, face, head and neck may also exhibit tremor in this disorder; the legs and feet are not usually involved. Head tremor may appear as a "yes-yes" or "no-no" movement while the affected individual is seated or standing. In some people with essential tremor, voice quality may be affected.
- Parkinsonian tremor is classically seen as a "pill-rolling" action of the hands but may also affect the chin, lips, legs, and trunk. It can be differentiated from essential tremor by the lack of improvement with medication or alcohol and by the presence of other symptoms.
- Dystonic tremor may also affect various parts of the body. The tremor of dystonia is often noticed more when a person moves a certain way. The tremor may go away when the body part is at rest.
- A cerebellar tremor is slower and of a wider radius than most of the other types. It tends to occur at the end of a purposeful movement (touching the finger to the nose). There are often other associated symptoms (gait disturbance, difficulty with speech, abnormal eye movements).
- Orthostatic tremor is associated with involuntary movement in the leg muscles which may not be easily visible.
- Psychogenic tremor often starts and ends abruptly and has a variable, unpredictable course that often doesn't fit a specific pattern.
The causes of tremor vary.
- Essential tremor appears to be an inherited disorder with an autosomal dominant inheritance pattern.
- Parkinson's tremor is caused by a disease that leads to degeneration of the nervous system and an impairment of movement control.
- Dystonic tremor is a symptom of the condition dystonia which may be inherited but also likely has environmental triggers.
- As stated previously, cerebellar tremor results from damage to the cerebellum from a variety of causes.
- The cause of orthostatic tremor is unknown.
- Psychogenic tremor also results from a variety of correctible causes.
Tremor is a common neurological sign; the diagnosis is mainly clinical. A coexistant disease process, such as Parkinson disease, alcoholism, stroke or multiple sclerosis may aid in diagnosis. Differentiating among the different types of tremor (involved body parts, frequency of movement) is often the key to diagnosis.
According to a 1995 study in the Western Journal of Medicine, , tremors vary in frequency and amplitude and are influenced by physiologic and psychological factors and drugs. Categorization is based on position, posture, and the movement necessary to elicit the tremor. A resting tremor occurs when the body part is in repose. A postural tremor occurs with maintained posture and kinetic tremor with movement. Various pathologic conditions are associated with tremors. Essential tremor, which is the most common, is postural and kinetic, with a frequency between 4 and 8 Hz, and involves mainly the upper extremities and head. Essential tremor responds to treatment with primidone, beta-blockers, and benzodiazepines. Parkinson's disease causes a 4- to 6-Hz resting tremor in the arms and legs that responds to the use of anticholinergics and a combination of carbidopa and levodopa.
There is no cure for most tremors. The appropriate treatment depends on accurate diagnosis of the cause.
Drug treatment for Parkinsonian tremor involves levodopa or dopamine-like drugs such as pergolide mesylate, bromocriptine mesylate, and ropinirole. Essential tremor may be treated with propranolol or other beta blockers (such as nadolol) and primidone (an anticonvulsant drug.) Dystonic tremor may respond to clonazepam, anticholinergic drugs, and intramuscular injections of botulinum toxin.
- Physical therapy may help to reduce tremor and improve coordination and muscle control for some patients.
- Surgical intervention, such as thalamotomy and deep brain stimulation, are usually performed only when the tremor is severe and does not respond to drugs. Deep brain stimulation involves the use of an implantable pacemaker in the brain to treat refractory tremor. It has been approved by the FDA as a treatment option for essential tremor, Parkinsonian tremor and dystonic tremor. Thalamotomy involves the surgical destruction of part of the thalamus. It can be an effective treatment, but is more invasive than deep brain stimulation.
- Psychotherapy may be helpful in the treatment of psychogenic tremor.
Living with Tremor
Although tremor is not life-threatening, it can still have a significant impact on the activities of daily living. Activities such as eating or drinking without spilling, speaking without a trembling voice, or writing legibly can become frustrating and challenging tasks.
- Eliminating tremor "triggers" such as caffeine and other stimulants from the diet is often recommended.
- As fatigue and stress may worsen tremor, getting plenty of sleep and trying to alleviate stress may be helpful.
- Although small amounts of alcohol may appear to improve tremor, chronic alcohol abuse may lead to withdrawl symptoms and may interfere with medicines used to treat tremor. Its use is discouraged.
- There may be other useful changes (only partially filling a cup or drinking with a straw, or weighting down the wrist to acheive a feeling of control) that may help lessen tremor.
Chances of Developing Tremor
Essential tremor can be passed through generations in families, but the inheritance pattern varies. In most affected families, essential tremor appears to be inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In other families, the inheritance pattern is unclear. Essential tremor may also appear in people with no previous history of the disorder in their family.
A list of ongoing U.S. government sponsored trials is available here
- A recent case report describes the successful treatment of orthostatic tremor with thalamic deep brain stimulation. 
- There may be an involvement of the dopaminergic system in some patients with orthostatic tremor. SPECT imaging appears to be able to distinguish between patients with greater involvement of the dopaminergic system (and therefore an increased likelihood of developing Parkinson disease in the future). 
- The long-term benefits of deep brain stimulation for patients with essential tremor were evaluated. Tremor remained decreased seven years after the procedure. The improvement in the activities of daily living was not as significant at this time, however. The study concluded that there was still a long-term benefit to deep brain stimulation in this group of patients. 
The prognosis for a tremor depends on the underlying cause. Some conditions, such as psychogenic tremor and orthostatic tremor, may be reversible. Tremor due to a permanent underlying disease process, such as multiple sclerosis or a stroke, are permanent, but may wax and wane during the course of the disease.
Essential tremor is a common disorder, affecting millions of people in the United States. Estimates of its prevalence vary widely because several other disorders, as well as certain medications and other factors, can result in similar tremors. Essential tremor may affect as many as 14 percent of people over the age of 65. 
- ↑ Anouti A, Koller WC. Tremor disorders. Diagnosis and management. West J Med. 1995 Jun;162(6):510-3. Abstract | Full Text
- ↑ Guridi J, Rodriguez-Oroz MC, Arbizu J, et al. Successful thalamic deep brain stimulation for orthostatic tremor. Mov Disord. 2008 Jul 31. [Epub ahead of print] Abstract
- ↑ Trocello JM, Zanotti-Fregonara P, Roze E, et al. Dopaminergic deficit is not the rule in orthostatic tremor. Mov Disord. 2008 Jul 25. [Epub ahead of print] Abstract
- ↑ Hariz GM, Blomstedt P, Koskinen LO. Long-term effect of deep brain stimulation for essential tremor on activities of daily living and health-related quality of life. Acta Neurol Scand. 2008 Jun 26. [Epub ahead of print] 18616684 Abstract
- ↑ Genetics Home Reference. Essential Tremor