Pathophysiology

The underlying mechanism of essential tremor is not known although several theories have been proposed. In a study of individuals with ET, results of an advanced imaging technique known as positron emission tomography (PET), which examines the biochemistry of the brain, suggested an abnormality in the olivo-cerebellar tracts of the brain. In addition, PET testing in patients with essential tremor reveals increased activity in one brain region known as the cerebellum even while at rest, a finding that is consistent with the cerebellum having an important role in the generation of tremor. Other researchers are investigating the role of stretch loop circuits as well as circuits within the central nervous system that may become unstable and drive muscle contractions (central oscillators), or a combination of both to produce tremor as in ET. A report published in 1997 about the role of clonidine in ET, lends support the theory of a central oscillating "pacemaker" in ET.

In another study,12 people with ET and 15 control subjects underwent functional magnetic resonance imaging (fMRI) studies of the brain. The results suggested that ET is mainly associated with an additional contralateral cerebellar pathway activation and overactivity in the cerebellum, red nucleus, and globus pallidus without significant intrinsic olivary activation.

It was reported that alcohol suppression of ET is mediated through a reduction in overactivity (cerebellar synaptic), resulting in an increased afferent input to the inferior olivary nuclei. The ingestion of ethanol led to bilateral decreases of cerebellar blood flow in both tremor patients and normal subjects, and this was associated with suppression of tremor in the patients. Moreover, alcohol-associated increases of regional cerebral blood flow were observed in the inferior olivary nuclei in the patients but not in the control subjects.

A group of drugs known as beta-adrenergic blockers such as propranolol are known to improve the symptoms associated with ET. It is possible that these beta-blockers work through peripheral beta₂ skeletal muscle adrenoreceptors (receptor mechanisms). However, beta-blockers may also affect central pathways.

More controlled studies are required to further investigate the underlying mechanisms of ET.

	Differential Diagnosis