Essential tremor

The term “essential tremor” was first used by European physicians in the later decades of the nineteenth century to describe an inherited, constitutional malady characterized by kinetic tremor in the absence of other neurological signs. Essential tremor (ET) may be defined simply as a progressive, neurological disease in which the most recognizable and primary motor feature is a kinetic tremor of the arms. Other motor and non-motor features are often present as well, but it is the kinetic tremor of the arms that is the sine qua non of ET. Considerable evidence has accumulated in recent years that ET is a cerebellar/cerebellar systems disorder. Clinically, the presence in ET patients of intention tremor, gait Ataxia, oculomotor abnormalities, and problems with dysrhythmia and motor learning converge upon the notion that ET is a disorder of cerebellar dysregulation. An array of neuroimaging studies indicate the presence not only of functional and metabolic abnormalities in the ET cerebellum, but of both gray and white matter structural abnormalities as well. In postmortem studies, the neuroanatomical changes in ET are thus far all localized to the cerebellum itself (esp. to Purkinje cells) or to a set of brainstem neurons that synapse directly with Purkinje cells. Additionally, deep brain stimulation surgery in ET targets the specific thalamic nucleus (ventral intermediate) that is the cerebellar receiving area. This chapter will expand upon the data underlying the emerging model of ET as a disorder of cerebellar structure and function.