Table of Contents
Primary Category
Movement Disorder
P-Category
Movement Disorder
Secondary Category
S-Category
Introduction
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
- 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.
- Usually no treatment is required for physiologic tremor.
- 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
- Consensus Statement on the Classification of Tremors. From the Task Force on Tremor of the International Parkinson and Movement Disorder Society. Kailash P. Bhatia, MD, FRCP, Peter Bain, MD, PhD, Nin Bajaj, MD, PhD, FRCP, Rodger J. Elble, MD, PhD, Mark Hallett, MD, PhD, Elan D. Louis, MD, Jan Raethjen, MD, PhD, Maria Stamelou, MD, PhD, Claudia M. Testa, MD, PhD, Guenther Deuschl, MD, PhD, (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6530552/).
Bibliography
- Lenka, A., & Jankovic, J. (2021). Tremor Syndromes: An Updated Review. Frontiers in Neurology, 12. 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 Neurology, 19(4), 433. https://doi.org/10.4103/0972-2327.194409
- Habib-ur-Rehman, N. A. (2000). Diagnosis and Management of Tremor. Archives of Internal Medicine, 160(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 Physician, 59(6), 1565. https://www.aafp.org/afp/1999/0315/p1565.html
