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Classification: Postural, Rest and Action Tremors
Tremor is primarily classified on the basis of when it occurs, either with a certain posture, at rest or during action (Table 1). A resting tremor occurs when the patient is attempting to maintain the position of a body part at rest (e.g., when the patient's hands exhibit a tremor as they are resting in the patient's lap). Postural tremor is observed when the patient tries to maintain a posture against gravity, such as holding the arms out in front of the body. An action tremor (kinetic or intention tremor) occurs during movement of the affected body part from one point to another. A task-specific tremor occurs only when the patient begins to perform a highly skilled activity, such as writing or speaking.2
Tremor may be either physiologic or pathologic. Physiologic tremor is a normal variant, occurring at a frequency of 8 to 12 Hz in the hands yet as slow as 6.5 Hz in other body parts during maintenance of a posture.2,4 It can be increased by emotions such as anxiety, stress or fear, by exercise and fatigue, hypoglycemia, hypothermia, hyperthyroidism and alcohol withdrawal. When such an increase occurs, physiologic tremor is then called enhanced or exaggerated physiologic tremor.1,4 Certain drugs can also exacerbate physiologic tremor5(Table 2). Pathologic tremor is either idiopathic or occurs secondary to some disorders(Table 3). Essential tremor and parkinsonian tremor are two common types of pathologic tremor.
Identification of the type of tremor depends on keen observation. The location of the tremor or the patient's position when it occurs should be identified first, and special attention must be paid to other signs of illness. Careful observation will reveal if the tremor occurs at rest, during posture maintenance or during movement. The patient should be asked what produces or modulates the amplitude and frequency of the tremor.2,3 A correct diagnosis is essential for proper treatment of the disorder, because different types of tremor require different treatments.
Commonly Used Agents That Exacerbate Physiologic Tremor
• Fluoxetine (Prozac)
• Haloperidol (Haldol)
• Methylphenidate (Ritalin)
|• Metoclopramide (Reglan)|
• Valproic acid
Selected Secondary Causes of Tremor
|• Alcohol or drug withdrawal|
• Brain abscess
• Brain tumor
• Multiple sclerosis
|• Peripheral neuropathy|
• Psychogenic disorders
Tremor Types Based on Causes
The tremor in Parkinson's disease occurs at rest and is characterized by a frequency of 4 to 6 Hz and a medium amplitude. It is classically referred to as a "pill rolling" tremor of the hands but can also affect the head, trunk, jaw and lips.2,3 Although rare, a rest tremor may also be found in patients with other neurodegenerative diseases, such as multiple-systems atrophy and progressive supranuclear palsy. The tremor associated with these disorders is usually symmetric and not as prominent as the tremor that accompanies Parkinson's disease.
|A physiologic tremor occurs in the hands at a frequency of 8 to 12 Hz during maintenance of a posture. |
Parkinson's disease results from a slow degeneration of a small area in the midbrain, called the substantia nigra. Specifically, excitatory and inhibitory dopaminergic neurons degenerate in the substantia nigra pars compacta. These neurons project to the striatum and then to the globus pallidus. From there, multiple connections in the basal ganglia project to one another, to the thalamus and, finally, to the cortex, which makes up the extrapyramidal system. This system regulates the initiation and control of movement, and dysfunction of any of these connections can lead to various types of movement disorders.6 As a consequence of neuronal degeneration in the substantia nigra pars compacta, the ventral intermediate nucleus of the thalamus becomes overactive, possibly producing the tremor of Parkinson's disease. The neurons in the ventral intermediate nucleus of the thalamus fire at a rate that matches the tremor.7
Essential tremor is the most common movement disorder.2,3,8 This postural tremor may have its onset anywhere between the second and sixth decades of life and its prevalence increases with age.8 It is slowly progressive over a period of years.3
The specific pathophysiology of essential tremor remains unknown. Essential tremor occurs sporadically or can be inherited. While the exact genetic defect has not been identified, familial transmission seems to be autosomal dominant with variable penetrance.4
The frequency of essential tremor is 4 to 11 Hz, depending on which body segment is affected. Proximal segments are affected at lower frequencies, and distal segments are affected at higher frequencies.3 Although typically a postural tremor, essential tremor may occur at rest in severe and very advanced cases.2 It most commonly affects the hands but can also affect the head, voice, tongue and legs.2,3,9 In some patients essential tremor is alleviated by small amounts of alcohol, an effect not found in Parkinson's disease.
The most common type of cerebellar tremor is kinetic, or goal directed. Cerebellar tremors are due to lesions of the lateral cerebellar nuclei or superior cerebellar peduncle, or its connections. Classically, a lesion within a cerebellar hemisphere or nuclei leads to an action tremor on the ipsilateral side of the body. Midline cerebellar disease may cause tremor of both arms, the head and the trunk.2 Lesions in the location of the red nucleus produce a wing-beating type of tremor (called rubral tremor), which is also present to a lesser degree with rest and posture.
During examination, a cerebellar tremor increases in severity as the extremity approaches its target. Other signs of cerebellar pathology, such as abnormalities of gait, speech and ocular movements, and the ability to perform rapidly alternating movements, may be present and may help to confirm the diagnosis of cerebellar tremor.3
|Propranolol (Inderal) and primidone (Mysoline) are both effective in the treatment of essential tremor. |
Another type of tremor may also be associated with damage to the cerebellum. Termed "cerebellar postural tremor," it is prominent with both action and posture.4 In its most severe form, cerebellar postural tremor has a frequency of 2.5 to 4 Hz and may wax and wane in amplitude, increasing progressively with prolonged posture. It persists and worsens with goal-directed movement.4 The milder form of the tremor has a more rapid frequency, approaching 10 Hz, and appears more distally, making it harder to identify than the severe type.4
Multiple sclerosis is the most common cause of the cerebellar postural tremor.4 Other causes of this tremor include tumors and strokes, as well as neural degeneration in the cerebellum.
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