Epidemiology and Etiology of Essential Tremor

Essential tremor is a chronic, progressive neurological disease. The motor feature that is the hallmark of the illness is a 4-12 Hz kinetic tremor that may involve several regions of the body, including the arms and head but rarely the legs (1-6).'The pathophysiology of this disorder is poorly understood. As with other rogressive neurological disorders of later life (e.g., motor neuron disease, parkinsonism), essential tremor may represent a family of related diseases rather than a single disease, and neurological manifestations as exhibited in any one patient may be dependent upon the localization of the disease pathology or pathologies within the nervous system. Thus, while the kinetic tremor in essen- tial tremor may be the result of an abnormality in an olivo-cerebellar-thalamic pathway, often patients with essential tremor have signs of more widespread cerebellar involvement (e.g., intention tremor, ataxia, eye movement abnormalities) (7-10), abnormalities of the basal ganglia (e.g., rest tremor d subtle bradyki-nesia) (11,12), and cognitive-neuropsychiatric manifestations that may be the result of abnormalities in cerebellar, subcortical, or cortical centers (13,14). In addition, involvement of the cerebellar-thalamic pathway and possibly other pathways in other progressive neurological diseases (e.g., Parkinson’s disease) can result in an action tremor, further increasing the clinical similarity between essential tremor and these diseases.