Essential tremor (ET) is a common neurological condition that is clinically diagnosed. Although several specific criteria exist, all require the presence of postural or action tremor in the arms without any other neurological conditions to account for such a tremor. Action tremor is identified in any scenario when those muscles are volitionally used. In contrast, rest tremor, which is characteristic for Parkinson's disease, occurs when the muscles are not volitionally engaged. For example, rest tremor may occur when the arms are resting on the patient's legs or when dangling while walking, while arm action tremor may occur when the patient is holding the arms in front (postural tremor) or moving the hand back and forth between two points (kinetic tremor). Intention tremor is also seen when moving between two points; however, the amplitude increases when approaching the targeted points. Intention tremor is usually seen in cerebellar pathology, such as multiple sclerosis. In short, postural, kinetic and intention tremor are all subsets of action tremor.
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