Essential Tremor (ET) is a neurological disorder characterized by shaking of hands (and sometimes other parts of the body including the head), evoked by intentional movements. The incidence is unknown, but is estimated to be as common as one person in 20, and it is the most common type of tremor and also the most commonly observed movement disorder.
Essential tremor generally presents as a rhythmic tremor (4-12 Hz) that is present only when the affected muscle is exerting effort (i.e., it is not present at rest). Any sort of physical or mental stress will tend to make the tremor worse, often creating the false impression that the tremor is of psychosomatic origin. It is typical for the tremor to worsen in "performance" situations, such as when making out a check at a checkout stand. This is probably due to the increased anxiety that a tremulous person experiences in such situations. ET-related tremors do not occur during sleep, but patients sometimes complain of an especially coarse tremor upon awakening that becomes noticeably less coarse within the first few minutes of wakefulness.
The cause of the disease is unknown. While no identifiable and consistent structural abnormality has been demonstrated yet to exist in the nervous system of every person with ET, researchers are searching actively for neurochemical and brain structure abnormalities that might be commonplace among people with ET.
Treatment of ET may or may not be attempted, depending on the severity of the tremor and the physical and social handicaps that implies. Drug treatment may include tranquilizers, beta-blockers, and antiepileptic drugs. Surgical treatments (which are generally reserved for the most severe cases) include botulism toxin injections into the affected muscles, thalamotomy, pallidotomy, and deep brain stimulation – the insertion of a "pacemaker" into the brain.