Enhanced Physiologic TremorĮnhanced physiologic tremor is a high-frequency, low-amplitude, visible tremor that occurs primarily when a specific posture is maintained. Neurologic examination results of patients with physiologic tremor are usually normal. It is present in every normal person while maintaining a posture or movement. Physiologic tremor is a very-low-amplitude fine tremor (6 Hz-12 Hz) that is barely visible to the naked eye. Signs and symptoms depend on tremor type and cause. Tremor can be classified on a clinical and etiologic basis. Positron emission tomography studies have shown cerebellar activation in almost all forms of tremor. Abnormal functioning of the cerebellum can produce tremor. Parkinsonian tremor might originate in the basal ganglia, and essential tremor might originate within the inferior olive and thalamus. These cells have the capacity to fire repetitively and produce tremor. Central oscillators are groups of cells in the central nervous system present in the thalamus, basal ganglia, and inferior olive. This mechanism is a possible cause of tremor in hyperthyroidism or other toxic states. Reflex oscillation is elicited by afferent muscle spindle pathways and is responsible for stronger tremors by synchronization. Mechanical oscillations of the limb can occur at a particular joint this mechanism applies in cases of physiologic tremor. 4-6 It is likely that combinations of these mechanisms produce tremor in different diseases. For whites in Europe and North America, the age-adjusted prevalence ratio ranges from 56 to 234 per 100,000 compared with a range of 14 to 148 per 100,000 in Asia.įour basic mechanisms are linked to the production of tremor. Population surveys for Parkinson's disease in different geographic regions of the world have shown a wide range of prevalence rates. He has designated this as emergent tremor and observes that the latency for the tremor to appear in Parkinson's disease (about 9 seconds) is significantly longer than the latency for essential tremor (about 1-2 seconds). According to Jankovic and colleagues, 3 postural tremor in Parkinson's disease patients can be distinguished from essential tremor by observing the latency, which is the timed interval starting with assumption of outstretched posture and ending with tremor onset. Parkinson's disease tremor generally occurs during rest, but some patients have postural and action tremor components. Age at onset of essential tremor has two peaks, early in life and in older age groups. 2 Family history is positively identified in approximately 60% of patients, and the pattern of inheritance is autosomal dominant. Essential tremor is the most common form, with a prevalence rate ranging from 0.4% to 5.6%. Prevalence rates vary, depending on the tremor type. Toxins (alcohol withdrawal, heavy metals) Metabolic disorders (thyrotoxicosis, pheochromocytoma, hypoglycemia)ĭrug-induced parkinsonism (lithium, amiodarone, β-adrenergic agonists) Examples of intention tremor include cerebellar tremor and multiple sclerosis tremor.īox 2: Examples of Postural and Action Tremors Intention (or terminal) tremor manifests as a marked increase in tremor amplitude during a terminal portion of targeted movement. An example of this type is primary writing tremor. Task-specific tremor emerges during a specific activity. Box 2 lists examples of postural and action tremors. Action or kinetic tremor occurs during voluntary movement. Postural tremor occurs during maintenance of a position against gravity and increases with action. Examples of resting tremor are provided in Box 1. Tremor amplitude decreases with voluntary activity. Resting tremor occurs when a body part is at complete rest against gravity. Common types include resting tremor, postural tremor, kinetic tremor, task-specific tremor, and intention tremor. In clinical practice, characterization of tremor is important for etiologic consideration and treatment. Tremor is defined as a rhythmic, involuntary, oscillating movement of a body part occurring in isolation or as part of a clinical syndrome. In 1817, James Parkinson characterized the tremor in his essay on the shaking palsy as "involuntary tremulous motion in parts not in action." 1 Tremor is the most common movement disorder.
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