Tremor
From Wikipedia, the free encyclopedia
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Tremor is an unintentional, somewhat rhythmic, muscle movement involving to-
and-from movements (oscillations) of one or more parts of the body. It is the most
common of all involuntary movements and can affect the hands, arms, head, face,
vocal cords, trunk, and legs. Most tremors occur in the hands. In some people,
tremor is a symptom of another neurological disorder. The most common form of
tremor, however, occurs in otherwise healthy people.
Causes
Tremor is generally caused by problems in parts of the brain or spinal cord that
control muscles throughout the body or in particular areas, such as the hands.
Neurological disorders or conditions that can produce tremor include multiple
sclerosis, stroke, traumatic brain injury and neurodegenerative diseases that
damage or destroy parts of the brainstem or the cerebellum. Other causes include
the use of some drugs (such as amphetamines, caffeine, corticosteroids, and
drugs used for certain psychiatric disorders), alcohol abuse or withdrawal,
mercury poisoning, overactive thyroid or liver failure. Tremors can be an
indication of hypoglycemia, along with palpitations, sweating and anxiety. Tremor
can also be caused from lack of sleep, vitamins, or having too much stress.
Deficiencies of magnesium and vitamin B1 have also been known to cause tremor
or shaking which resolves when the deficiency is corrected. See magnesium in
biology. Some forms of tremor are inherited and run in families, while others have
no known cause. Tremors can also be caused by some spider bites i.e. the
redback spider of Australia.
Characteristics may include a rhythmic shaking in the hands, arms, head, legs, or
trunk; shaky voice; difficulty writing or drawing; or problems holding and
controlling utensils, such as a fork. Some tremors may be triggered by or become
exaggerated during times of stress or strong emotion, when the individual is
physically exhausted, or during certain postures or movements.
Tremor may occur at any age but is most common in middle-aged and older
persons. It may be occasional, temporary, or occur intermittently. Tremor affects
men and women equally.
Etiologies
Tremor is most commonly classified by clinical features and cause or origin. Some
of the better known forms of tremor, with their symptoms, include the following:
Essential tremor (sometimes called benign essential tremor) is the most
common of the more than 20 types of tremor. Although the tremor may be mild and
nonprogressive in some people, in others, the tremor is slowly progressive,
starting on one side of the body but affecting both sides within 3 years. The hands
are most often affected but the head, voice, tongue, legs, and trunk may also be
involved. Head tremor may be seen as a “yes-yes” or “no-no” motion. Essential
tremor may be accompanied by mild gait disturbance. Tremor frequency may
decrease as the person ages, but the severity may increase, affecting the person’
s ability to perform certain tasks or activities of daily living. Heightened emotion,
stress, fever, physical exhaustion, or low blood sugar may trigger tremors and/or
increase their severity. Onset is most common after age 40, although symptoms
can appear at any age. It may occur in more than one family member. Children of a
parent who has essential tremor have a 50 percent chance of inheriting the
condition. Essential tremor is not associated with any known pathology.
Parkinsonian tremor is caused by damage to structures within the brain
that control movement. This resting tremor, which can occur as an isolated
symptom or be seen in other disorders, is often a precursor to Parkinson's
disease (more than 25 percent of patients with Parkinson’s disease have an
associated action tremor). The tremor, which is classically seen as a “pill-rolling”
action of the hands that may also affect the chin, lips, legs, and trunk, can be
markedly increased by stress or emotions. Onset of parkinsonian tremor is
generally after age 60. Movement starts in one limb or on one side of the body and
usually progresses to include the other side.
Dystonic tremor occurs in individuals of all ages who are affected by
dystonia, a movement disorder in which sustained involuntary muscle contractions
cause twisting and repetitive motions and/or painful and abnormal postures or
positions. Dystonic tremor may affect any muscle in the body and is seen most
often when the patient is in a certain position or moves a certain way. The pattern
of dystonic tremor may differ from essential tremor. Dystonic tremors occur
irregularly and often can be relieved by complete rest. Touching the affected body
part or muscle may reduce tremor severity (a geste antagoniste). The tremor may
be the initial sign of dystonia localized to a particular part of the body.
Cerebellar tremor (also known as "intention tremor") is a slow, broad tremor
of the extremities that occurs at the end of a purposeful movement, such as trying
to press a button or touching a finger to the tip of one’s nose. Cerebellar tremor is
caused by lesions in or damage to the cerebellum resulting from stroke, tumor, or
disease such as multiple sclerosis or some inherited degenerative disorder. It can
also result from chronic alcoholism or overuse of some medicines. In classic
cerebellar tremor, a lesion on one side of the brain produces a tremor in that same
side of the body that worsens with directed movement. Cerebellar damage can
also produce a “wing-beating” type of tremor called rubral or Holmes’ tremor — a
combination of rest, action, and postural tremors. The tremor is often most
prominent when the affected person is active or is maintaining a particular
posture. Cerebellar tremor may be accompanied by other manifestations of ataxia,
including dysarthria (speech problems), nystagmus (rapid, involuntary rolling of
the eyes), gait problems and postural tremor of the trunk and neck.
Psychogenic tremor (also called hysterical tremor) can occur at rest or during
postural or kinetic movement. The characteristics of this kind of tremor may vary
but generally include sudden onset and remission, increased incidence with
stress, change in tremor direction and/or body part affected, and greatly
decreased or disappearing tremor activity when the patient is distracted. Many
patients with psychogenic tremor have a conversion disorder or another
psychiatric disease.
Orthostatic tremor is characterized by fast (>12Hz) rhythmic muscle
contractions that occur in the legs and trunk immediately after standing. Cramps
are felt in the thighs and legs and the patient may shake uncontrollably when
asked to stand in one spot. No other clinical signs or symptoms are present and
the shaking ceases when the patient sits or is lifted off the ground. The high
frequency of the tremor often makes the tremor look like rippling of leg muscles
while standing. Orthostatic tremor may also occur in patients who have essential
tremor.
Rubral tremor is characterized by coarse slow tremor which is present at rest,
at posture and with intention. This tremor is associated with conditions which
affect the red nucleus in the midbrain, classically unusual strokes.
Physiologic tremor occurs in every normal individual and has no clinical
significance. It is rarely visible to the eye and may be heightened by strong
emotion (such as anxiety or fear), physical exhaustion, hypoglycemia,
hyperthyroidism, heavy metal poisoning, stimulants, alcohol withdrawal or fever. It
can be seen in all voluntary muscle groups and can be detected by extending the
arms and placing a piece of paper on top of the hands. Enhanced physiologic
tremor is a strengthening of physiologic tremor to more visible levels. It is
generally not caused by a neurological disease but by reaction to certain drugs,
alcohol withdrawal, or medical conditions including an overactive thyroid and
hypoglycemia. It is usually reversible once the cause is corrected.
Tremor can result from other conditions as well. Alcoholism, excessive alcohol
consumption, or alcohol withdrawal can kill certain nerve cells, resulting a tremor
known as asterixis. Conversely, small amounts of alcohol may help to decrease
familial and essential tremor, but the mechanism behind this is unknown. Tremor in
peripheral neuropathy may occur when the nerves that supply the body’s muscles
are traumatized by injury, disease, abnormality in the central nervous system, or as
the result of systemic illnesses. Peripheral neuropathy can affect the whole body
or certain areas, such as the hands, and may be progressive. Resulting sensory
loss may be seen as a tremor or ataxia (inability to coordinate voluntary muscle
movement) of the affected limbs and problems with gait and balance. Clinical
characteristics may be similar to those seen in patients with essential tremor.
Diagnosis
During a physical exam a doctor can determine whether the tremor occurs
primarily during action or at rest. The doctor will also check for tremor symmetry,
any sensory loss, weakness or muscle atrophy, or decreased reflexes. A detailed
family history may indicate if the tremor is inherited. Blood or urine tests can
detect thyroid malfunction, other metabolic causes, and abnormal levels of certain
chemicals that can cause tremor. These tests may also help to identify contributing
causes, such as drug interaction, chronic alcoholism, or another condition or
disease. Diagnostic imaging using CT or MRI imaging may help determine if the
tremor is the result of a structural defect or degeneration of the brain.
The doctor will perform a neurological exam to assess nerve function and motor
and sensory skills. The tests are designed to determine any functional limitations,
such as difficulty with handwriting or the ability to hold a utensil or cup. The
patient may be asked to place a finger on the tip of her or his nose, draw a spiral,
or perform other tasks or exercises.
The doctor may order an electromyogram to diagnose muscle or nerve problems.
This test measures involuntary muscle activity and muscle response to nerve
stimulation.
Categories
The degree of tremor should be assessed in four positions. The tremor can then
be classified by which position most accentuates the tremor: [1]
Position Name Description
At rest Resting tremors Tremors that are worse at rest include
Parkinsonian syndromes and essential tremor if severe. This includes drug-
induced tremors from blockers of dopamine receptors such as haloperidol and
other antipsychotic drugs.
During contraction (eg a tight fist while the arm is resting and supported)
Contraction tremors Tremors that are worse during supported contraction include
essential tremor and also cerebellar and exaggerated physiologic tremors such as
a hyperadrenergic state or hyperthyroidism[1]. Drugs such as adrenergics, anti-
cholinergics, and xanthines can exaggerate physiologic tremor.
During posture (eg with the arms elevated against gravity such as in a 'bird-
wing' position) Posture tremors Tremors that are worse with posture against
gravity include essential tremor and exaggerated physiologic tremors.
During intention (eg finger to nose test) Intention tremors Intention tremors
are tremors that are worse during intention, e.g. as the patient's finger
approaches a target, including cerebellar disorders.
Treatment
There is no cure for most tremors. The appropriate treatment depends on accurate
diagnosis of the cause. Some tremors respond to treatment of the underlying
condition. For example, in some cases of psychogenic tremor, treating the patient’
s underlying psychological problem may cause the tremor to disappear.
Medications
Symptomatic drug therapy is available for several forms of tremor:
Parkinsonian tremor drug treatment involves levodopa and/or dopamine-like
drugs such as pergolide mesylate, bromocriptine mesylate and ropinirole. Other
drugs used to lessen parkinsonian tremor include amantadine hydrochloride and
anticholinergic drugs.
Essential tremor may be treated with propranolol, nadolol or other beta blockers
and primidone, an anticonvulsant drug.
Cerebellar tremor typically does not respond to medical treatment.
Rubral tremor patients may receive some relief using levodopa or anticholinergic
drugs.
Dystonic tremor may respond to Valium, anticholinergic drugs, and intramuscular
injections of botulinum toxin. Botulinum toxin is also prescribed to treat voice and
head tremors and several movement disorders.
Primary orthostatic tremor sometimes is treated with a combination of Valium and
primidone.
Enhanced physiologic tremor is usually reversible once the cause is corrected. If
symptomatic treatment is needed, beta blockers can be used.
Lifestyle
Eliminating tremor “triggers” such as caffeine and other stimulants from the diet is
often recommended.
Physical therapy may help to reduce tremor and improve coordination and muscle
control for some patients. A physical therapist will evaluate the patient for tremor
positioning, muscle control, muscle strength, and functional skills. Teaching the
patient to brace the affected limb during the tremor or to hold an affected arm
close to the body is sometimes useful in gaining motion control. Coordination and
balancing exercises may help some patients. Some therapists recommend the use
of weights, splints, other adaptive equipment, and special plates and utensils for
eating.
Surgery
Surgical intervention such as thalamotomy and deep brain stimulation may ease
certain tremors. These surgeries are usually performed only when the tremor is
severe and does not respond to drugs.
Thalamotomy, involving the creation of lesions in the brain region called the
thalamus, is quite effective in treating patients with essential, cerebellar, or
parkinsonian tremor. This in-hospital procedure is performed under local
anesthesia, with the patient awake. After the patient’s head is secured in a metal
frame, the surgeon maps the patient’s brain to locate the thalamus. A small hole is
drilled through the skull and a temperature-controlled electrode is inserted into
the thalamus. A low-frequency current is passed through the electrode to activate
the tremor and to confirm proper placement. Once the site has been confirmed,
the electrode is heated to create a temporary lesion. Testing is done to examine
speech, language, coordination, and tremor activation, if any. If no problems
occur, the probe is again heated to create a 3-mm permanent lesion. The probe,
when cooled to body temperature, is withdrawn and the skull hole is covered. The
lesion causes the tremor to permanently disappear without disrupting sensory or
motor control.
Deep brain stimulation (DBS) uses implantable electrodes to send high-frequency
electrical signals to the thalamus. The electrodes are implanted as described
above. The patient uses a hand-held magnet to turn on and turn off a pulse
generator that is surgically implanted under the skin. The electrical stimulation
temporarily disables the tremor and can be “reversed,” if necessary, by turning off
the implanted electrode. Batteries in the generator last about 5 years and can be
replaced surgically. DBS is currently used to treat parkinsonian tremor and
essential tremor.
The most common side effects of tremor surgery include dysarthria (problems with
motor control of speech), temporary or permanent cognitive impairment (including
visual and learning difficulties), and problems with balance.
Biomechanical loading
As well as medication, rehabilitation programmes and surgical interventions, the
application of biomechanical loading on tremor movement has been shown to be a
technique that is able to suppress the effects of tremor on the human body. It has
been established in the literature that most of the different types of tremor
respond to biomechanical loading. In particular, it has been clinically tested that
the increase of damping and/or inertia in the upper limb leads to a reduction of the
tremorous motion. Biomechanical loading relies on an external device that either
passively or actively acts mechanically in parallel to the upper limb. This
phenomenon gives rise to the possibility of an orthotic management of tremor.
Starting from this principle, the development of upper-limb non-invasive
ambulatory robotic exoskeletons is presented as a promising solution for patients
who cannot benefit from the use of medication to suppress the tremor. In this area
robotic exoskeletons have emerged, in the form of ortheses, to provide motor
assistance and functional compensation to disabled people. An orthosis is a
wearable device that acts in parallel to the affected limb. In the case of tremor
management, the orthosis must apply a damping or inertial load to a selected set
of limb articulations.
Recently, some studies demonstrated that exoskeletons could achieve a
consistent 40% of tremor power reduction for all users, being able to attain a
reduction ratio in the order of 80% tremor power in specific joints of users with
severe tremor [2]. In addition, the users reported that the exoskeleton did not
affect their voluntary motion. These results indicate the feasibility of tremor
suppression through biomechanical loading.
The main drawback of this mechanical management of tremor is: (1) the resulting
bulky solutions, (2) the inefficiency in transmitting loads from the exoskeleton to
the human musculo-skeletal system and (3) technological limitations in terms of
actuator technologies. In this regard, current trends in this filed are focused on
the evaluation of the concept of biomechanical loading of tremor through
selective Functional Electrical Stimulation (FES) based on a (Brain-to-Computer
Interaction) BCI-driven detection of involuntary (tremor) motor activity. [3]
Tremors