Enhanced Physiological Tremor

Enhanced physiological tremor is the most commonly observed postural tremor. Physiologic tremor is undetectable, low amplitude and high frequency (10-12 Hz) tremor in normal individuals. Sympathetic hyperactivity causes enhanced physiological tremor that can be detected on observation.

 

Introduction

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Enhanced physiological tremor is the most commonly observed postural tremor.
  • Physiologic tremor is undetectable, low amplitude and high frequency (10-12 Hz) tremor in normal individuals.
  • Sympathetic hyperactivity causes enhanced physiological tremor that can be detected on observation.

Etiology

  • Increased sympathetic activity is the most important cause of these tremors.
  • Caused by variety of physiological states, pathological conditions, drugs and toxins.

Table 1: Etiological causes of enhanced physiological tremor

Pathophysiology

  • Enhancement of the normal mechanical reflex due to sympathetic hyperactivity causes these tremors.
  • Mechanical component is activated by the spinal stretch reflex.
  • Central component consists of a neural oscillator at 8–12 Hz.
  • There are unstable interactions between central tremor generators and the biomechanics of the spinal stretch reflex.

Clinical Manifestations

  • Characterized as a visible low amplitude and high frequency postural or kinetic tremor.
  • Symmetrically involves bilateral hands and all fingers.
  • Affects fine finger movement precision.
  • Tremor appears only under certain conditions such as stress, fatigue, anxiety, medication use, or caffeine intake.
  • The central component has a frequency of 8 to 12 Hz.
  • Frequency gradually decreases with age to 6 to 7 Hz in persons older than 60 years.
  • Application of large inertia loads on the tremulous limb decreases the frequency.
  • Tremor is amplified by placing a sheet of paper on outstretched hands.
  • Amplitude can be modulated by temperature, supraspinal influences(vision) and drugs interacting with β receptors.
  • Associated clinical signs and symptoms can help in distinguishing different causes.

Table 2: Clinical manifestations and investigations of pathological causes of EPT

Diagnosis

  • New-onset tremor should be evaluated with comprehensive medication review.
  • In case of action tremor, priority is given to identify a medical cause instead of primary neurological pathology.
  • Enhanced physiological tremor is only diagnose when all other etiologies have been ruled out.
  • Diagnosis is confirmed when a specific etiology is found.
  • Accelerometer and EMG can be used to objectively confirm these tremors.
  • Electrophysiological studies are helpful in distinguishing mild ET from enhanced physiological tremor.
  • Electrophysiological studies identifies 3 components in these tremors including mechanical component, mechanical-reflex component, and central component.
  • In physiological tremor, there is usually only a mechanical component with no EMG correlation.
  • Metabolic profile, blood glucose levels, liver function tests, thyroid function tests helps to exclude pathological causes.
  • 24-hour urine fractionated metanephrines/catecholamines or plasma fractionated metanephrines are performed if suspicion of pheochromocytoma.

Differential Diagnosis

  • Essential tremor: Electrophysiological studies are used to differentiate mild ET from enhanced physiological tremor.
  • Parkinsonian tremor: Pathognomonic symptoms of PD (bradykinesia, rigidity, REM sleep behaviour disorder) are not present in enhanced physiological tremor.
  • Monosymptomatic resting tremor: Dopamine transporter imaging can be used to confirm diagnosis.
  • Cortical myoclonus: Repetitive rhythmic muscle jerks with somatosensory evoked potentials (SEPs) and series of EMG bursts.
  • Tardive dyskinesia: Nonrhythmic and involuntary movements and postures associated with the use of dopamine receptor-blocking agents.

Treatment

  • Usually no treatment is required for physiologic tremor.
  • Needs identification and removal of the precipitating cause.
  • Relaxation sessions have been shown to decrease tremor significantly.
  • Propranolol may be effective if precipitating cause cannot be removed.
  • Propranolol (160 mg/day) is effective in reducing tremor of alcohol withdrawal.
  • Correction of electrolytes and blood glucose levels in case of abnormal metabolic profile.
  • α and β adrenergic blockade is achieved prior to surgical resection of pheochromocytoma with phenoxybenzamine and metoprolol/propranolol, respectively.
  • Atenolol 25 to 50 mg daily aids in symptomatic relief in thyrotoxicosis before euthyroidism is achieved by definitive treatment.

Prognosis

  • It is a benign condition.
  • Mostly reversible if causative agent is identified and corrected.

Further Reading

Bibliography

  • Lenka, A., & Jankovic, J. (2021). Tremor Syndromes: An Updated Review. Frontiers in Neurology12. https://doi.org/10.3389/fneur.2021.684835
  • View Image. (2022). Annalsofian.org. https://www.annalsofian.org/viewimage.asp?img=AnnIndianAcadNeurol_2016_19_4_433_194409_t2.jpg
  • Pandey, S., & Sharma, S. (2016). Approach to a tremor patient. Annals of Indian Academy of Neurology19(4), 433. https://doi.org/10.4103/0972-2327.194409
  • Habib-ur-Rehman, N. A. (2000). Diagnosis and Management of Tremor. Archives of Internal Medicine160(16), 2438. https://doi.org/10.1001/archinte.160.16.2438
  • P. David Charles, Esper, G. J., Davis, T. J., Maciunas, R. J., & Robertson, D. (1999). Classification of Tremor and Update on Treatment. American Family Physician59(6), 1565. https://www.aafp.org/afp/1999/0315/p1565.html