General Classification of Tremor

Authors:

Muhammad Ehtesham Javed,

Muhammad Roshan Asghar MD,

Adeel Memon MD

Introduction

• 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:

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:

1. Frequency

2. Amplitude

3. Anatomical distribution

4. 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.

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.

Activation Pattern

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

• Broadly categorized into rest tremor and action tremor.

• Generated by voluntary contraction of a muscle.

• Further divided into kinetic and isometric tremor.

• 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.

• 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.

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

Isolated tremor syndromes

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

• 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.

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

• 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.

• 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.

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

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

• Action tremor that occurs exclusively during writing.

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

• Postural tremor of legs and trunks occurs exclusively while standing.

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

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

• 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).

• 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).

• Palatal tremor with coexisting neurological signs and symptoms.

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

• 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.

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

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

• 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.

• 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.

• 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;

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

• Manifests variable tremor frequency and tremor entrainment with distraction maneuvers.

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

Further Reading

1. Bhatia, K. P., Bain, P., Bajaj, N., Elble, R. J., Hallett, M., Louis, E. D., Raethjen, J., Stamelou, M., Testa, C. M., Deuschl, G., & Tremor Task Force of the International Parkinson and Movement Disorder Society (2018). Consensus Statement on the classification of tremors. from the task force on tremor of the International Parkinson and Movement Disorder Society. Movement disorders : official journal of the Movement Disorder Society, 33(1), 75–87. https://doi.org/10.1002/mds.27121

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

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