1. Essential Tremor: Classification, Diagnosis, and Management
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Part 1 of 7

2. Tremor Defined
An involuntary, rhythmic, oscillatory, sinusoidal movement of a part or parts of the body
Produced by contractions of alternating or synchronous antagonist muscles
Essential tremor or ET is a common, though under-recognized, movement disorder that may cause significant functional disability. ET has previously been termed benign essential tremor; senile tremor when seen in elderly patients; or familial tremor. Unfortunately, for many clinicians as well as the general population, inclusion of the word “benign” before ET has inappropriately trivialized or minimized the impact of ET on quality of life, functional disability, handicap, and overall burden of illness.
As with other forms of tremor, ET is characterized by involuntary, rhythmic oscillations of a part or parts of the body produced by synchronous or alternating contractions of antagonist muscles.

3. Classification of Tremor
Rest tremor
Action tremor
Postural tremor
Reemergent tremor
Kinetic tremor
Initial tremor
Dynamic tremor
Terminal tremor
Task- or position-specific tremor
Isometric tremor
Tremors may be categorized based upon the behavioral circumstances under which they occur, such as during intentional muscle activation, sustained posture, and goal- or non goal-directed movements. For example, resting tremors are present when a body part is fully supported against gravity in a manner not necessitating voluntary activation of skeletal muscles. This type of tremor may often be suppressed upon voluntary muscle contraction. Action tremors occur upon voluntary muscle contraction and may include any combination of postural, kinetic, task- or position-specific, and isometric tremor. Postural tremor is present upon voluntarily attempting to maintain a position against the force of gravity, such as pointing or sitting erect without support. In other words, postural tremor may be limited to or exacerbated by particular postures. Kinetic tremor occurs during voluntary movements, including visually or non -visually guided actions, such as speaking, pouring water into a cup, or finger-to-nose testing. Intention tremor may be described as a kinetic tremor that occurs with target-directed movements. Simple kinetic tremors are present during voluntary actions that are not target directed.
Task- or position-specific tremor occurs during the performance of specialized, complex activities involving certain motor groups. Such tremor includes primary writing tremor and task-specific tremor seen in some musicians. Isometric tremors are present during voluntary muscle contraction against a rigid stationary object, such as making a fist or flexing the wrist against a horizontal, flat surface. So-called “mixed tremors” include rest, postural, and kinetic elements.
Essential tremor is generally described as a postural or kinetic intention tremor or a combination of these tremor types.

4. Clinical Classification of Tremors
NIH: Collaborative Genetic Criteria (1996)
Tremor Investigation Group (TRIG) (1995)
Consensus Statement of the Movement Disorder Society (MDS) (1997)
Use of such clinical classifications stimulates
discussions and thus contributes to the
development of tremor research.
Practical classifications of tremor based upon etiologic or pathophysiologic factors remain unavailable. Therefore, tremor research typically relies on clinical classifications, such as the NIH Collaborative Genetic Criteria; the Tremor Investigation Group or TRIG Criteria; and the Consensus Statement of the Movement Disorder Society on Tremor.
Clinicians and academic scientists differ in their views concerning tremor classification; therefore, the development of such criteria is considered fundamental in communicating minimal consensus, describing the clinical spectrum of tremors with common terminology, and providing a setting that promotes the resolution of remaining questions. Accordingly, these criteria are intended to stimulate discussions that will contribute to tremor research and the establishment of consistent tremor definitions and diagnostic criteria.

5. Clinical Classification of Tremor Based on...
Phenomenology: rest; action as in postural, kinetic (including simple kinetic or intention), or isometric
Anatomic or topographic distribution
Activities that activate tremor
Relative frequency of tremor (cycles per second)
Medical history/evaluation/current meds (primary/secondary tremor)
The clinical classification of tremor may be based upon phenomenology and activation conditions; anatomic region affected; tremor frequency; and the presence of any coexistent neurologic conditions, use of tremorogenic medications, or other causative states. Relative tremor frequency—as measured by cycles per second—is classified as low at less than 4 Hz; medium, ranging from 4 to 7 Hz; or high, at greater than 7 Hz.

6. ET Anatomic Distribution (n=350)
This slide illustrates the topographic distribution of tremor in 20 index patients with hereditary ET and their kindreds.
ET most frequently affects the hands, often as an isolated finding. Although hand tremor is usually bilateral, it may initially be noted in the dominant hand, eventually progressing to affect both sides. The hand tremor is typically biphasic, with flexion-extension movement of hand muscles and adduction-abduction finger movements. Less commonly, tremor may be characterized by pronation-supination movements of the hand and the forearm. The frequency of the tremor ranges between 4 to 12 Hz.
ET also commonly affects the head. Although isolated head tremor is not rare, this form of tremor most frequently occurs subsequent to upper limb tremors. Less commonly, this tremor may precede hand tremor by a number of years. Thus, head tremor that appears to occur in isolation must be excluded from abnormal posturing associated with cervical dystonia. Head tremor is typically in a horizontal “no-no” pattern in about 75% of ET patients; the remainder affected by vertical a “yes-yes” tremor. Voice, tongue, and palatal tremors may also develop, leading to dysarthric speech. Less commonly, ET may involve muscles of the trunk and lower limbs, particularly with advanced stages of disease.
ET is generally described as a slowly, yet variably progressive monosymptomatic disorder that is not associated with increased mortality. Disease progression is typically defined as an increase in tremor amplitude and associated impairment of voluntary movements. In contrast, with disease advancement, tremor frequency tends to decrease. In some patients, disease progression may include extension of tremor to other muscle groups and anatomic regions.
Bain PG, Findley LJ, Thompson PD, Gresty MA, Rothwell JC, Harding AE, Marsden CD. A study of hereditary essential tremor. Brain. 1994;117 (Pt 4):

7. Classification Based on Activation Condition
This slide illustrates classification based upon the activation conditions under which tremor occurs. Tremor activation may occur during full support of the affected body part, holding a body part steady against gravity, or goal-directed or non goal directed skeletal muscle movement.
ET is generally a postural or kinetic tremor or combination of these tremor types; however, some patients with advanced ET may develop resting or mixed tremor, which may be confused with Parkinson’s disease (PD). Diagnostic criteria for PD include at least 2 of 3 cardinal signs: bradykinesia, rigidity, and tremor, primarily at rest. In addition postural or kinetic tremor with similar or higher, frequencies may be present ; less commonly, isolated postural/kinetic tremors may be present.
Physiologic and enhanced physiologic tremors may be categorized as postural tremors--as may midbrain or Holmes, neuropathic, and dystonic tremors. For example, many patients with dystonia also have a postural hand tremor that may be difficult to differentiate from ET. In addition, in patients with cervical dystonia, head tremor may be present that tends to be irregular, occurs with tilting of the head or chin, and varies in intensity with position changes. In contrast, in ET patients, head tremor is characterized by rhythmic, regular oscillations.
In patients with Wilson’s disease, neurologic symptoms may include dystonia, bradykinesia, ataxia, dysphagia, dysarthria, and so-called “wing-beating” tremor in which tremor is exacerbated upon stretching the limbs. Also classified as kinetic tremors are cerebellar, task-specific, and midbrain tremors—as well as tremors associated with MS, cerebrovascular insults, and certain degenerative conditions.
Many conditions may be misinterpreted as tremor. These may include contraction fasciculations; clonus or rhythmic, uniphasic contractions and relaxations of muscle groups; rhythmic myoclonus, or epilepsia partialis continua. This focal motor epilepsy is associated with recurrent, rhythmic clonic movements of a specific muscle group. In addition, asterixis is a condition in which sudden, periodic interruptions in muscle contraction lead to arrhythmic lapses of sustained posture associated with EMG pauses ranging from about 35 to 200 milliseconds or greater.

8. Classification of Tremor Based on Relative Frequency (Hz)
Frequency in Hz
Typical Etiology
Cerebellar, “ataxic” (brainstem,MS)
PD (rest), rubral, neuroleptic-induced
ET, PD (postural), drug (VPA), voluntary (max. 6 Hz)
Physiological, exaggerated physiologic, drug-induced (e.g., epinephrine)
Tremors may also be classified based on frequency or the number of complete wave forms per second. Physiologic and enhanced physiologic tremor have a relatively high frequency, often ranging from approximately 7 to 12 cycles per second. In contrast, the rate of many pathologic tremors is about 2 to 7 Hz. Orthostatic tremor is a notable exception, with a 13 to 18 Hz entrainment of motor unit activity as confirmed by EMG. In addition, cortical tremor, recognized as a form of rhythmic myoclonus, is characterized by irregular, postural and kinetic tremor-like jerks with a range between 7 to 18 Hz.
Cerebellar and rubral or Holmes tremors tend to be of relatively low frequency, primarily occurring below 4.5 or 5 Hz. The frequency of a pure rest tremor observed in PD is characteristically greater than 4 Hz, although the upper frequency limit has not been firmly established.
In classic ET, the rate of tremor may vary between 4 to 12 Hz, with older patients typically demonstrating tremor frequencies toward the lower range. In contrast, younger patients with mild ET tend to have tremor frequencies that extend into the 7 to 12 Hz range, similar to that of physiologic tremor.

9. 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)
Tremor severity may be measured using clinical rating scales, evaluating tremor based on handwriting or Archimedes spirals, and using objective functional performance tests, such as the 9-hole pegboard test or the amount of water spilled from a cup. For example, the NIH Collaborative Genetic Criteria are based upon the following Tremor Severity Scale.
Zero equals none—no tremor impairment is present.
One equals minimal, barely noticeable tremor—no tremor impairment or associated functional disability is present.
Two equals noticeable, mild tremor—characterized by less than 2 cm excursions. Tremor is probably not disabling.
Three equals moderate tremor—characterized by 2 to 4 cm excursions. Tremor is probably partially disabling.
Four equals severe, coarse tremor—greater than 4 cm excursions. Functional disability is typically present.

10. NIH Collaborative Genetic Criteria: Possible ET
Isolated 1+ cranial/cervical tremor Or
Task- or position-specific arm tremor
Unilateral arm tremor
Orthostatic tremor
The NIH Collaborative Genetic Criteria categorize possible ET based upon confirmation of...
Isolated cranial or cervical tremor with a 1+ amplitude rating or
Task- or position-specific upper limb tremor, which occurs upon performance of specific, highly specialized motor activities, or
Unilateral arm tremor or
Orthostatic tremor.
Exclusion criteria for possible ET are the same as previously mentioned.

11. Tremor Consensus Statement
Clinical diagnostic framework for tremor:
Nomenclature
Definitions based upon phenomenology
Work-up/evaluation
Rating scales
Differential diagnosis
Supporting technical investigations
Deuschl G, Bain P, Brin M, and an Ad Hoc Scientific Committee. Consensus statement of
the Movement Disorder Society on tremor. Mov Disord 1998;13 (suppl 3):2-23.
The Consensus Statement of the Movement Disorder Society on Tremor was formulated during the Society’s tremor symposium in Kiel, Germany in Subsequently approved by the Society’s Scientific Issues Committee and Executive Committee, the Consensus Statement represents the Society’s proposal for a clinical classification of tremor.
The main purpose of the statement is to communicate consistent nomenclature concerning tremor classification, thereby promoting clinical research with clearly defined patient populations. The Consensus report provides a diagnostic framework by describing the clinical spectrum of tremor based upon phenomenology; conveying common terminology regarding the clinical assessment of tremor, such as activation condition and frequency; and discussing the use of tremor rating scales. The MDS statement also describes syndromic and etiologic classifications of tremor, syndromes that may be mistaken for tremor, and technical investigations that may assist in tremor diagnosis and monitoring. The MDS also advocates use of a randomized, double-blind, placebo-controlled study design for therapeutic trials; a thorough battery of tests including neurophysiologic assessments to evaluate the efficacy of medical therapies; and specific sequences during videotaped recordings of patients to help standardize clinical presentation during diagnostic assessments for rest, postural, simple kinetic, and intention tremors.

12. Classic ET: Exclusion Criteria, (cont.)
5. Primary orthostatic tremor
6. Isolated voice tremor
7. Isolated position- or task-specific tremors
8. Isolated tongue or chin tremor
9. Isolated leg tremor
(Kiel, Germany; MDS Symposium, July 1997)
Additional exclusion criteria for classic ET include confirmation of...
Primary orthostatic tremor
Isolated voice tremor
Isolated position- or task-specific tremors
Isolated tongue or chin tremor
Isolated leg tremor
Isolated voice tremors may be defined as tremulousness of the voice in the absence of other tremor manifestations--or a focal dystonia of the vocal cords, such as tremor that subsides with changes in pitch or gestes antagonistes. Isolated position- and task-specific tremors include primary writing tremor, defined as tremor occurring solely or primarily while writing. Other hand activities are not affected by writing tremor. Also included are occupational tremors that are present during the performance of highly skilled motor activities, such as specific tremors affecting athletes or musicians.