Essential Tremor

Clinical Classification of Tremors

Because practical classifications of tremor that are based upon etiologic or pathophysiologic factors are not available, tremor research typically relies on clinical classifications. The clinical classification of tremor may be based upon...

• Clinical phenomenology
• Anatomic or topographic distribution
• Activities that activate tremor
• Relative tremor frequency measured in cycles per second
• Medical and drug history and clinical evaluation (i.e., to detect concomitant neurologic conditions, drug-induced or toxic tremors, etc.)

The definition of the clinical classification of ET is an ongoing, evolutionary process. Several classification schemes have been proposed, including the Tremor Investigation Group (TRIG) Criteria in 1995; the National Institutes of Health (NIH) Collaborative Genetic Criteria in 1996 [refer to table 2]; and the Consensus Statement of the Movement Disorder Society (MDS) on Tremor in 1997 [refer to table 3]. The use of such classification schemes may stimulate discussion among physicians regarding the definition of ET, leading to a clinical diagnostic framework for tremor including nomenclature; definitions based upon phenomenology, evaluation, and rating scales; differential diagnosis; and support for technical investigations. Such a definition may play an essential role in facilitating appropriate, early identification of ET and assisting in the development of new approaches to tremor research.

Table 2. NIH Collaborative Genetic Criteria*
Tremor Severity Scale:	0= None 1= Minimal (barely noticeable) 2= Obvious, noticeable but probably not disabling    (<2 cm excursions) 3= Moderate, probably partially disabling    (2 cm to 4 cm excursions) 4= Severe, coarse, and disabling (>4 cm excursions)
Definite ET:	2+ amplitude rating for bilateral arm tremor    or 2+ amplitude rating in one arm and 1+ amplitude rating in other arm    or 1+ amplitude rating in at least one arm and predominant cranial/cervical tremor with 2+ amplitude rating Head tremor is rhythmic with no directional preponderance and without asymmetry of cervical muscles. Exclude: obvious secondary causes (coexistent dystonia allowed; coexistent PD disallowed)
Probable ET:	1+ bilateral arm tremor    or Isolated 2+ cranial/cervical tremor    or Convincing history of ET Exclude: obvious secondary causes (e.g., enhanced physiologic tremor, drug-induced or toxic tremor, coexistent peripheral neuropathies [such as CMT], etc.) Coexistent dystonia allowed Coexistent PD allowed if there is a convincing history of pre-existing ET
Possible ET:	Isolated 1+ cranial/cervical tremor    or Task- or position-specific arm tremor    or Unilateral arm tremor    or Orthostatic tremor
Unrateable ET:	Tremor is coexistent with other neurologic disease, therapy with anti-tremor or tremor-promoting drugs, untreated thyroid disease, caffeine withdrawal/abstention, etc.

Table 3. Consensus Statement of the Movement Disorder Society**
Classic ET: Inclusion Criteria	Bilateral, largely postural or kinetic tremor involving the hands and forearms Tremor is persistent and visible
Classic ET: Exclusion Criteria	Other abnormal neurologic signs (particularly dystonia) Presence of known causes of enhanced physiologic tremor Historical or clinical evidence of psychogenic tremor Convincing evidence of sudden onset or stepwise deterioration Primary orthostatic tremor Isolated voice tremor Isolated position- or task-specific tremor Isolated tongue or chin tremor Isolated leg tremor