Tremor is defined as an unintentional, rhythmic, oscillatory muscle contraction causing shaking movements of one or more parts of the body. It can affect the hands, head, face, jaw, lips, torso, and legs. Sometimes the voice may be affected as well.
Hand tremor is the most common form.
Tremor is a normal physiologic phenomenon. Most of us see our hands shaking slightly when we hold them out in front of us. Several factors, such as stress, anxiety, lack of sleep, smoking, and caffeine may exaggerate this tremor.
Although tremor is usually not a sign of a severe or life-threatening medical disorder, it can be both embarrassing and disabling to some people and make it harder to perform work and daily life tasks.
Tremor may occur at any age but is most common in middle-aged and older adults. It tends to affect men and women equally.
Tremors are classified as rest or action tremors.
Rest tremor occurs when the affected body part is completely supported against gravity. It may be an arm or a hand that is resting in the patient’s lap. Action tremors, on the other hand, are produced by voluntary muscle contraction. They may occur when writing or lifting a cup of coffee.
Postural tremor is a sub-type of action tremors and occurs when the person maintains a position against gravity such as holding the arms outstretched (1). Postural and action tremors, including exaggerated physiologic tremor and essential tremor, comprise the largest groups.
1. Exaggerated Physiologic Tremor
All normal persons exhibit physiologic tremor. However, it may often be invisible to the naked eye.
Physiological tremor is most evident in the outstretched hands but can be detected in the legs, head, trunk, jaw, and lips.
Enhanced physiologic tremor may be caused by medical conditions such as thyrotoxicosis (overactive thyroid gland), hypoglycemia (low blood sugar), the use of certain drugs, or withdrawal from alcohol, opioids or benzodiazepines. It is usually reversible once the cause is corrected (1).
2. Essential Tremor
Essential tremor is the most common neurologic disorder that causes postural or action tremor. It is also the most common movement disorder worldwide.
The prevalence increases markedly with age and ranges from 4.1 to 39.2 cases per 1,000 persons, to as high as 50.5 per 1,000 in persons older than 60 years (4). These figures may underestimate the actual prevalence, however, because up to 50 percent of persons with mild essential tremor are unaware of it (5).
More than half of patients with essential tremor have a family history of the disorder (6).
Essential tremor usually develops insidiously and progresses slowly. It often occurs first in the hands and forearms and may be more prominent on one side of the body and increases with goal-directed activity (e.g., drinking from a glass of water or writing).
Essential tremor may also affect the head, voice, jaw, lips, and face. It can include a”yes-yes” or “no-no” motion of the head.
The shaking usually increases with stress, fatigue, and certain medications such as central nervous stimulants. It may also increase with specific voluntary activities such as holding a spoon or a cup.
Interestingly, there is often a degree of voluntary control. Hence, the trembling may be suppressed by performing skilled manual tasks (7).
Although sometimes disabling, essential tremor is in itself a benign disorder and not life-threatening.
Rest, beta blockers, primidone (Mysoline), and alcohol ingestion decrease the trembling.
Primidone and propranolol are the cornerstones of maintenance medical therapy for essential tremor. These medications provide clinical benefit in approximately 50-70% of patients (8).
3. Parkinson’s Disease
Although Parkinson’s disease is probably 20 times less common than essential tremor, about one million Americans suffer from the disease (9).
Tremor is a common symptom of Parkinson’s disease and other Parkinsonian syndromes. However, it is not experienced by all patients with Parkinson’s disease.
The tremor includes shaking in one or both hands at rest. It may also affect the chin, lips, face, and legs. The shaking may initially appear in only one limb or on just one side of the body. It is often made worse by stress, strong emotions, and after exercise.
Sometimes, the trembling only affects the hand or fingers. This type of shaking is often seen in people with Parkinson’s disease and is called a “pill-rolling” tremor because the circular finger and hand movements resemble rolling of small objects or pills in the hand.
Although the trembling of Parkinson’s disease is usually defined as a resting tremor, more than 25 percent of people with Parkinson’s disease also have an associated action tremor (10).
The trembling of Parkinson’s disease differs from essential tremor in three fundamental ways (11):
- Essential tremor is more likely to occur during voluntary activity of the hands whereas the trembling of Parkinson’s disease is more prominent at rest.
- Parkinson’s disease is usually associated with stooped posture, slow movement, and shuffling gait.
- Essential tremor mainly involves the hands, head, and voice. Parkinson’s disease tremors usually start in the hands and arms but also affect the legs, chin, and other parts of your body.
Although Parkinson’s disease can’t be cured, medications may markedly improve symptoms.
4. Intention Tremor (Cerebellar Tremor)
Intention tremor, also known as cerebellar tremor, presents as a unilateral or bilateral shaking, most often caused by stroke, brainstem tumor, or multiple sclerosis (1).
The neurological examination will reveal that finger-to-nose, finger-to-finger, and heel-to-shin testing result in increased shaking as the extremity approaches the target. Other signs include abnormalities of gait, speech, and ocular movements and inability to perform rapid alternating hand movements.
That the shaking typically increases in severity as the hand moves closer to its target, is in contrast to postural and action tremor (like essential tremor), which either remains constant throughout the range of motion or abruptly increase at terminal fixation (12).
Ataxia, a lack of voluntary coordination of muscle movements that includes gait abnormality, is typically associated with cerebellar tremor.
5. Wilson Disease
Wilson disease is a rare autosomal recessive inherited disorder of copper metabolism that is characterized by excessive deposition of copper in the liver, brain, and other tissues (13). Wilson disease is often fatal if not recognized and treated when symptomatic.
Liver dysfunction is the presenting feature in more than half of patients.
The most common presenting neurologic feature is an asymmetric tremor, which is variable in character.
Wilson disease may also be associated with difficulty speaking, excessive salivation, ataxia, clumsiness with the hands, and personality changes.
6. Rubral Tremor
Rubral tremor, also known as Holmes tremor, is a rare symptomatic movement disorder, characterized by a combination of resting, postural, and action tremors.
It is usually caused by lesions involving the brainstem, thalamus, and cerebellum.
The disorder is often difficult to treat. Many medications have been used with varying degrees of success (14).
7. Primary Writing Tremor
Shaking that occurs exclusively while writing, and not during other voluntary motor activities, is referred to as primary writing tremor. Hence, it is a task-specific tremor that predominantly occurs and interferes with handwriting (15).
The cause and pathophysiology of this disorder are still unknown. It has been classified as a focal form of essential tremor and as a tremulous form of writer’s cramp (16).
Botulinum toxin injections and deep brain stimulation may be treatment choices for primary writing tremor (17).
8. Orthostatic Tremor
Orthostatic tremor is a rare disorder, characterized by a rapid trembling limited to the legs and trunk (18). It occurs exclusively while standing.
The disorder is often associated with extreme straining of both legs, fatigue, unsteadiness and a fear of falling. Standing upright for only a short period may be difficult.
The shaking may disappear partially or completely when an affected person is walking or sitting.
There is controversy within the medical literature regarding whether orthostatic tremor is a variant of essential tremor, an exaggerated physiological response to standing still or a distinct clinical entity (19).
The disorder may respond to treatment with clonazepam or gabapentin (Neurontin) (20).
9. Functional Tremor (Psychogenic Tremor)
Functional tremor, also known as psychogenic tremor, is a variable tremor that may decrease or disappear when not under direct observation.
Functional tremor is classified as a functional movement disorder, a term that is applied to disorders that manifest with physical symptoms, specifically abnormal movements (gait disorders, tremor, dystonia, etc.) but which cannot be attributed to any of known underlying organic disorders and which instead is presumed to be due to “psychological factors” (21).
Any body part may be involved, but, remarkably, the fingers are often spared with much of the trembling of the arm occurring at the wrist (12).
A characteristic that suggests functional rather than organic tremors is abrupt onset with immediate maximal severity, often precipitated by trivial emotional or physical trauma (22).
Patients with functional tremor often have more than one movement disorder, which can be a helpful clue to the diagnosis.
10. Drug-Induced Tremors
Several medications can cause or exacerbate tremor (1).
Examples are amiodarone, atorvastatin, beta-adrenergic agonists (albuterol, terbutaline, salbutamol) carbamazepine, corticosteroids, fluoxetine, haloperidol, lithium, methylphenidate, synthetic thyroid hormones, tricyclic antidepressants, valproic acid, and verapamil.
The shaking may affect the hands, arms, head, or eyelids. It rarely affects the lower body and may not always affect both sides of the body equally (23).
Drug-induced tremor will usually disappear when the medication causing the symptoms is stopped.
If the benefit of the medicine is greater than the problems caused by the tremor, lowering the dose may sometimes be helpful.