ABSTRACT
I. Introduction 13
II. Case Definition and Diagnosis 14
III. Specific Methodological Considerations 15
IV. Prevalence 16
V. Incidence 16
VI. Progression 17
VII. Mortality 17
VIII. Risk Factors 18
IX. Etiology 19
A. Genetic vs. Nongenetic Etiologies 19
B. Genetic Etiologies 20
C. Environmental Etiologies 21
X. Summary 22
References 22
I. INTRODUCTION
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
progressive 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 cer-
ebellar involvement (e.g., intention tremor, ataxia, eye movement abnormalities)
(7-10), abnormalities of the basal ganglia (e.g., rest tremor and 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.
