General Classification of Tremor

Primary Category

Movement Disorder

P-Category

Secondary Category

S-Category

Authors:

Muhammad Ehtesham Javed,
Muhammad Roshan Asghar MD,
Adeel Memon MD

Introduction

💡

The most prevalent movement disorder encountered in primary care.

Defined as an involuntary, rhythmic, and oscillatory movement of a body part.

May occurs in healthy individuals as enhanced physiologic tremor.

Induced by alternating or synchronous contractions of reciprocally innervated antagonist muscles.

History and physical examination (position, posture, and activation pattern) aid in diagnosis.

Clinical rating scales and electrophysiological measurements are utilized in evaluating the severity and therapeutic response.

Epidemiology

Enhanced physiologic tremor, essential tremor, and Parkinsonian tremor are more prevalent.

Older people are more commonly affected as ~5% of the population over the age of 40 years have tremor.

Classification of Tremor

Tremors are classified and interpreted differently.

Various tremor syndromes have overlapping features and etiologies.

May differ in frequency and amplitude.

Induced by physiological & psychological factors and drugs.

A clinical and etiological classification strategy has been recommended by International Parkinson and Movement Disorder Society.

Fundamental parameters utilized in tremor classification are:

(a) Phenomenological parameters.

(b) Etiological causes.

Classification based on phenomenological parameters

Phenomenology of tremor assists in classification and diagnosis.

It includes clinical features manifested during history and physical assessment.

The following parameters are valuable during examination:

Frequency

Amplitude

Anatomical distribution

Activating conditions

Tremor Frequency

Frequency is the number of vibrations per second.

Gauged by EMG or Accelerometers.

Various disorders may have overlapping frequencies.

Parkinsonian tremors, myorhythmia, and some palatal tremors have a frequency below 4 Hz.

The frequency of primary orthostatic tremors is 13 to 18 Hz.

Essential tremors and central neurogenic components of physiological tremors have a frequency of 5-10 Hz.

A frequency of <4 Hz is observed in severe cerebellar tremors, but up to 10 Hz may be seen in mild distal cerebellar tremors.

Table 1: Subdivision of tremor based on the frequency

Categories	Frequency	Tremor Types
(a) Low Frequency Tremor	<4Hz	Parkinsonian tremor, cerebellar tremor, holmes tremor, palatal tremor, drug-induced tremor. intention tremor.
(b) Intermediate Frequency Tremor	4-8 Hz	Physiological tremor, Essential tremor, Task-specific tremor, Dystonic tremor, Neuropathic tremor, Palatal tremor, Drug-induced tremor, Psychogenic tremor.
(c) High Frequency Tremor	8-12 Hz	Orthostatic tremor, Essential tremor, Physiological tremor.
(d) Very high frequency	>12 Hz	Primary orthostatic tremor
(e) Variable frequency	ㅤ	Psychogenic tremor.

Amplitude of Tremor

The extent of linear or angular displacement elicited about the fixed plane.

Accurately scaled in millimetres or degrees by accelerometers or gyroscopes.

Coarse tremor: have large amplitude and low irregular frequency, that includes parkinsonian and holmes tremors.

Fine tremor: have low amplitude and high frequency, includes enhanced physiological and essential tremor.

Anatomical Distribution

Tremors may be unifocal, multifocal, or generalized.

May involve the head, face, jaw, vocal apparatus, tongue, trunk, or extremities.

Table 2: Anatomical distribution of tremor

Categories	Discription	Tremor types
(a) Focal tremor	Single body region is affected.	Voice tremor, Head tremor, Palatal tremor, Task-specific tremor,
(b) Segmental tremor	Two or more contiguous body parts in the upper or lower body are affected.	Cervical dystonia, Segmental tremulous dystonia,
(c) Hemi-tremor	One side of the body is affected.	Rest tremor combined with parkinsonism, Intention tremor, Myorhythmia, Holmes’ tremor,
(d) Generalized tremor	Effects the upper and lower body.	Cerebellar tremor, Enhanced physiological tremor, Psychogenic tremor, Orthostatic tremor, Essential tremor, Drug-induced tremor.
(e) Proximal tremor	Tremor affecting proximal limb musculature, has high amplitude and low frequency.	ㅤ
(f) Distal tremor	Low amplitude and high frequency tremors affecting distal limb muscles.	ㅤ

Activation Pattern

Tremor is primarily classified based on its occurrence with a certain posture.

Broadly categorized into rest tremor and action tremor.

Figure 1: Categories of tremor based on the activation pattern

Action tremor

💡

The essential tremor is the most commonly encountered action tremor.

Generated by voluntary contraction of a muscle.

Further divided into kinetic and isometric tremor.

Table 3: Subdivision of Action tremor

Types of Tremor	Definition	Sub-types	Clinical features and Provocative maneuvers
Kinetic tremor	Elicited by voluntary movement.	(a) Task-specific kinetic tremor while doing a specific task. (b) Simple-kinetic tremor non-specific to any activity (c) Intention tremor while performing goal-directed activities.	Finger-to-nose test, heel-to-shin test, reaching, writing, drawing, pouring water into a cup, eating with utensils, speaking, doing specific tasks for task specific tremor.
Isometric tremor	Evoked during sustained muscle contraction against a rigid stationary object.	ㅤ	Pushing against a wall, flexing the wrist against table, making a fist.

Resting tremor

💡

Resting tremor is most commonly found in Parkinson’s disease.

Elicited in part that is not voluntarily activated.

Assessed when the affected body part is relaxed and completely supported against gravity.

Amplitude increases with mental stress, cognitive tasks, and the activity of another body part.

Subsides with the activity of the affected limb.

(a) Parkinsonian resting tremor: Seen In Parkinson's disease, spinocerebellar ataxia, Wilson's disease, Multisystem atrophy, and drugs.

(b) Monosymptomatic resting tremor: Observed in essential, holmes, dystonic, thalamic tremor, and SWEDDs (Scans without evidence of dopaminergic deficits).

Postural tremor

Emerges during voluntary maintenance of a specific posture held against gravity.

Amplitude increases during the voluntary movement.

Evaluated during upper limb extension, object pointing, sitting upright without support, standing, and tongue protrusion.

Usually exhibits the frequency of 5-9 Hz.

Comprises enhanced physiological, drug-induced, essential, and psychogenic tremors.

Subdivided into a positional-dependent and positional-independent postural tremor.

Etiological Classification of Tremor

Tremor has marked etiological heterogeneity.

Can be due to genetic, acquired, or idiopathic etiologies.

Prognosis and specific treatment plans are determined by underlying etiology.

Physiologic Tremor, is an 8-12 Hz normal variant that occurs during the maintenance of a posture.

Physiologic tremor is increased by emotions, fatigue, stress, exercise, alcohol withdrawal, and drugs.

Pathologic tremor is either idiopathic or occurs secondary to some disorders.

Essential tremor and Parkinsonian tremor are the two most common types of pathologic tremor.

Table: 4 Etiological causes of tremor

Etiology	Diseases
Physiological causes	Emotions (fear, stress, anxiety), exercise, fatigue.
Neurodegenerative diseases	Parkinson’s disease, Multiple system atrophy, Corticobasal degeneration, Frontotemporal dementia with Parkinsonism, Spinocerebellar ataxias, Wilson’s disease, Lesch-Nyhan’s syndrome, Fragile X–associated tremor/ataxia syndrome, Spinal muscular atrophy.
Drugs	Anticonvulsants (valproate, carbamazepine, phenytoin), Tetrabenazine, antidepressants, sympathomimetics, bronchodilators, beta-2 agonists, Lithium, Neuroleptics, metoclopramide, Amiodarone, Thyroid hormone replacement, Anticancer drugs (vincristine, cisplatin, paclitaxel, doxorubicin, cytosine arabinoside, ifosfamide, tacrolimus, 5-fluorouracil, methotrexate), Drug and alcohol withdrawal.
Toxins	Mercury, Lead, Manganese, Arsenic, Cyanide, DDT, CO, Naphthalene, Toluene, Lindane
Chromosomal aneuploidy	XYY, XXY (Klinefelter’s syndrome), and XXYY syndromes.
Mitochondrial genetic disorders	Leigh’s syndrome, Mitochondrial polymerase gamma mutations.
Infectious and other inflammatory diseases	Demyelinating diseases such as multiple sclerosis, Encephalitis lethargica, subacute sclerosing panencephalitis, HIV, Tuberculosis, syphilis, measles, typhus, neuroborreliosis, Bacterial or viral encephalitis, Antineuronal antibody disease.
Endocrine and metabolic disorders	Nephrotic or liver failure, hyperthyroidism. hypoglycemia
Neuropathies and spinal muscular atrophies	Kennedy’s syndrome, Guillain-Barre’s syndrome, Gammopathy-induced neuropathies.
Others	Brain neoplasms, Brain injury (head trauma, brain surgery, and electrical injury), Vascular (ischemia, hemorrhage, and arteriovenous malformations), Anxiety and stress, Fatigue, Cooling, Trauma of peripheral tissues, HIV, human immunodeficiency virus.

Classification based on Tremor Syndromes

Categorization is based on associated neurological or systemic signs and symptoms.

Examination of cranial nerves, speech, gait, balance, and muscle tone may assist in clinical diagnosis.

This classification helps in clinical and research purposes.

Helps in explaining new syndromes without etiological inferences.

Preliminary classification may be altered with the manifestation of new clinical features.

Multiple etiologies might be associated with a tremor syndrome

Table 5: Subdivision of tremor syndromes

Types	Syndromes
Isolated tremor syndromes	Essential tremor, Essential tremor plus, Voice tremor, Head tremor, Jaw tremor, Essential Palatal tremor, Face tremor, Primary orthostatic tremor, Pseudo orthostatic tremor, Task specific writing/musician’s/sport tremor.
Combined tremor syndromes	Dystonic tremor, Parkinsonism-associated tremor, Intention tremor (with cerebellar signs), Holmes tremor(with brainstem & cerebellar signs), Myorhythmia (with brainstem & cerebellar signs), Symptomatic palatal tremor.
Other syndromes	Functional tremor, Indeterminate tremor.

Isolated tremor syndromes

Tremor is the only clinical manifestation, without any other abnormal neurological or systemic signs.

(i) Essential tremor

Bilateral upper limb action or postural tremor without additional neurological signs.

High-frequency tremor with an increase in amplitude at the end of goal-directed activities.

(ii) Essential tremor plus

Bilateral upper limb action tremor, with additional neurological signs of uncertain significance.

(iii) Isolated voice tremor

Tremor of vocal apparatus in the absence of dystonia or other neurological signs.

Causes periodic fluctuations in pitch and loudness of voice with voice-less pauses.

(iv) Isolated head tremor

Head Tremor in the absence of any obvious cervical dystonia or tremor of other body parts.

Causes shaking of the head in yes-yes, no-no, or variable directions.

(v) Essential palatal tremor

Isolated focal tremor of the soft palate, often with audible clicks.

They have a frequency of 1-7 Hz and completely cease during sleep.

(vi) Primary writing tremor

Action tremor that occurs exclusively during writing.

Causes low frequency and high amplitude supination-pronation movements limited to hands.

(vii) Orthostatic tremor

Postural tremor of legs and trunks occurs exclusively while standing.

(viii) Enhanced Physiological Tremor

Symptomatic, bilateral upper extremity action tremor with a frequency of 9-12 Hz

Caused by fatigue, anxiety, stress, fear emotions, drugs, hypoglycemia, and thyrotoxicosis.

(ix) Isolated rest tremor (SWEDD)

Isolated resting tremor of arm resembling early PD that fails to evolve into more generalized PD over time.

No evidence of nigrostriatal dopamine deficiency on imaging.

Combined tremor syndromes

Tremors with associated abnormal neurological or systemic signs (dystonia, rigidity, bradykinesia, myoclonus, Kayser-Fleischer ring, hepatosplenomegaly, or exophthalmos).

(i) Dystonic tremor

Postural, task-specific, or rest tremor in a body part that is affected by dystonia.

Irregular, jerky tremor that alleviates by maneuvers (sensory tick or geste antagoniste).

(ii) Symptomatic palatal tremor

Palatal tremor with coexisting neurological signs and symptoms.

They have a lower frequency(1.5–3 Hz) and usually persist during sleep.

(iii) Cerebellar tremor

Low-frequency action tremor in the presence of other cerebellar signs (ataxia, dysmetria, titubation).

Increases in severity as the hand move closer to the target.

(iv) Neuropathic tremor

Action tremor of arms/hands, in the presence of severe peripheral neuropathies.

Frequency and amplitude vary greatly when associated with a proprioceptive deficit.

(v) Parkinsonism-associated tremor

Low amplitude pin-rolling resting tremor is a characteristic feature of Parkinson's disease.

Occurs in a body part that is reposed, relaxed, and completely supported against gravity.

(vi) Holmes tremor

A subtype of cerebellar tremor with high amplitude and low frequency occurring at rest.

Persists unchanged or increases with postural change or goal-directed activity.

(vii) Myorhythmia

Slow, rhythmic, repetitive jerky movements involving cranial and limb muscles.

Associated with other neurological signs (dystonia, palatal tremor, and abnormal eye movements)

Other tremor syndromes

They include syndromes that can not be categorized into either isolated or combined syndromes;

(i) Functional tremor

Abrupt onset complex tremor with a static course, changeable features and spontaneous remission.

Manifests variable tremor frequency and tremor entrainment with distraction maneuvers.

(ii) Indeterminate Tremor

Classic essential tremor with neurologic signs not sufficient to make a diagnosis of a recognizable neurologic disorder.

Figure 2: Clinical identification of the major tremor syndromes

CitLenka A and Jankovic J (2021) Tremor Syndromes: An Updated Review. Front. Neurol. 12:684835. doi: 10.3389/fneur.2021.684835 — CitLenka A and Jankovic J (2021) Tremor Syndromes: An Updated Review. *Front. Neurol.* 12:684835. doi: 10.3389/fneur.2021.684835

Bibliography

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