Tremor is the most common movement disorder. It is also probably the oldest sign in medicince as the quote from the Book of Psalms testifies to: "the Lord reignth, let the people tremble." In 1817, James Parkinson characterized the tremor in his essay on The Shaking Palsy. "Involuntary tremulous motion in parts not in action

Tremor is defined as a rhythmic, involuntary, oscillating movement of a body part occurring in isolation or as part of a clinical syndrome. In clinical practice, characterization of tremor is important for etiologic consideration and treatment.


Physiological Tremor

This is a very-low-amplitude fine tremor (between 6 Hz and 12 Hz) that is barely visible to the naked eye. It is present in every normal individual during maintaining a posture or movement. Neurologic examination results of patients with physiologic tremor are usually normal.

Enhanced Physiologic Tremor

This is a high-frequency, low-amplitude, visible tremor that occurs primarily when a specific posture is maintained. Drugs and toxins induce this form of tremor. The suspected mechanism is mechanical activation at the muscular level. Signs and symptoms of drug toxicity or other side effects may or may not be present. Tremor symptoms may improve after discontinuation of the causative agent.

Essential Tremor

Essential tremor is the most common form of all movement disorders. Classical essential tremor is predominantly a postural- or action-type tremor and usually patient has positive family history of tremor. Drinking alcohol often temporarily reduces the tremor. Other associated symptoms may include mild gait difficulty and, as a group, patients with essential tremor have increase hearing disability compared to controls or patients with Parkinson's Disease. The degree of hearing impairment seems to correlate with the tremor severity.

Parkinson's Tremor

This is a low-frequency rest tremor typically defined as a pill-rolling tremor. In some patients, postural and action tremor may also occur. Parkinson's tremor usually occurs in association with other symptoms, such as micrographia, slowness (bradykinesia), and rigidity. Usually, there is no family history of Parkinson's tremor, and alcohol consumption does not decrease movement

Cerebellar Tremor

Cerebellar tremor is a low-frequency (less than 4 Hz) intention tremor that usually occurs unilaterally. Common causes are multiple sclerosis, stroke, and cerebellar injury. Signs and symptoms of cerebellar dysfunction may be present, including ataxia, dysmetria, dysdiadokinesia and dysarthria.

Holmes' Tremor

The term Holmes' tremor or rubral tremor designates a combination of rest, postural, and action tremors due to midbrain lesions in the vicinity of the red nucleus.5 This type of tremor is irregular and slow frequency (4.5 Hz). Signs of ataxia and weakness may be present. Common causes include cerebrovascular accident and multiple sclerosis, with a possible delay of 2 weeks to 2 years in tremor onset and occurrence of lesions.

Drug-induced Tremor

Types of tremors induced by drugs include enhanced physiologic tremor, rest tremor, and action tremor. Signs and symptoms of drug-induced tremors depend on the drug used and on a patient's predisposition to its side effects. Some drugs cause extrapyramidal side effects manifesting as bradykinesia, rigidity, and tremor. Table 4 is a list of drugs that may induce tremor, along with the types of tremors and neurologic signs they produce. It has recently been observed that tremor reappears in Parkinson's patients treated with cholinesterase inhibitors reinforcing the observation that anticholingergic agents are very effective in amelurating the tremor of Parkinson's Disease.

Tremor Due to Systemic Disease

Tremor due to systemic disease usually occurs when the patient is moving or assumes a specific position. Associated symptoms include asterixis, mental status changes, and other signs of systemic illness. Diseases such as thyrotoxicosis and hepatic failure as well as delirium tremens and drug withdrawal are among the common causes.

Psychogenic Tremor

Psychogenic tremor may involve any part of the body, but it most commonly affects the extremities. Usually, tremor onset is sudden and begins with an unusual combination of postural, action, and resting tremors. Psychogenic tremor decreases with distraction and is associated with multiple other psychosomatic complaints.

Orthostatic Tremor

Orthostatic tremor is considered to be a variant of essential tremor. This type of tremor occurs in the legs immediately on standing and is relieved by sitting down. Orthostatic tremor is usually high frequency (14 Hz to 18 Hz), and no other clinical signs and symptoms are present.


Diagnostic evaluation of the tremor patient should include a thorough clinical history, clinical examination (including tremor rating), and differential diagnosis.

Definite essential tremor:

Postural tremor in the arms which increases during action in the absence of any condition or drug known to cause enhanced physiological tremor and in the absence of cerebellar symptoms and signs, and in the absence of PD and dystonia. Head tremor may or may not be present.

Probable essential tremor:

Postural tremor in the arms without increase during action in the absence of any condition or drug known to cause enhanced physiological tremor and in the absence of cerebellar symptoms and signs, and in the absence of PD and dystonia. Vocal and head or neck tremor in the absence of any condition or drug known to cause enhanced physiological tremor and in the absence of cerebellar symptoms and signs, and in the absence of PD and dystonia.

Possible essential tremor:

Postural tremor in the arms and action tremor in arms in the absence of any condition or drug known to cause enhanced physiological tremor and in the absence of cerebellar symptoms and signs, but in the presence of PD and dystonia.

Clinical History

The clinical history must detail tremor onset, duration, severity, affected area, activating factors, relieving factors, effect of alcohol, family history, and associated symptoms.

Clinical Examination

The clinical examination should determine a tremor rating and tremor frequency. The patient also should be examined during rest, when assuming various positions, and when moving. An examination of gait, muscle tone, facial expressions, and dexterity is also important, particularly in differentiating essential tremor from Parkinson's disease.

Tremor in each affected body part can be rated as resting, kinetic, or postural with a scale developed by Kahn et al as follows:

0 - No tremor
1 - Slight tremor
2 - Moderate tremor (less than 2 cm excursion)
3 - Marked tremor (2 cm to 4 cm excursion)
4 - Severe tremor (more than 4 cm excursion)

Laboratory Work-up

A laboratory work-up is not necessary for most tremor patients. A thyroid function test is helpful to rule out hyperthyroidism in patients with signs of thyroid disease and tremor, particularly postural and action types. In young patients (younger than 40 years of age) with signs of parkinsonism and tremor, a serum copper, serum ceruloplasmin, 24-h urinary copper, and slit-lamp examination is necessary to rule out Wilson's disease. To rule out systemic causes of tremor, such as hypoglycemia, liver disease, electrolyte imbalance, or drug abuse, appropriate tests should be ordered. A magnetic resonance imaging or computed tomography scan of the brain is needed in some patients if tremor onset is acute, progression is rapid, and cerebellar signs suggest stroke, demyelinating disease, or structural lesion. Tremor also can be analyzed and diagnosed with the help of accelerometers and surface electromyogram (EMG) recordings.

Differential Diagnosis

Differential diagnosis of tremor includes myoclonus, clonus, asterixis, and epilepsia partialis continua. Myoclonus is irregular or rhythmic brief muscle jerks that can mimic tremor. Electrophysiologic analysis by EMG or electroencephalogram (EEG) as well as back-averaging help to make the diagnosis. Clonus is a rhythmical movement around joints that is stimulated through stretch reflex. Passive stretching increases the clonus but not of tremor, helping to differentiate clonus from tremor. Asterixis is a type of myoclonus that can cause a flapping tremor of the extremities. Asterixis can be differentiated from tremor on the basis of irregular movements. In addition, EMG readings show pauses longer than 200 msec. Epilepsia partialis continua can cause rhythmic jerks in the extremities. A clinical history that is positive for epilepsy and EEG readings that show abnormal spikes help point to the correct diagnosis.