Is Essential Tremor Bilateral?
Yes, essential tremor is characteristically bilateral—the American Academy of Neurology defines it as bilateral action tremor of the arms and hands present for at least 3 years, making bilateral involvement a diagnostic requirement. 1
Diagnostic Criteria for Essential Tremor
The bilateral nature of essential tremor is fundamental to its diagnosis:
Essential tremor must present as bilateral action tremor primarily affecting the arms and hands to meet diagnostic criteria, distinguishing it from other tremor disorders that may present unilaterally. 1
The tremor is described as "largely symmetric postural or kinetic tremor involving hands and forearms that is visible and persistent," emphasizing the bilateral distribution. 2
An updated 2018 consensus statement redefined essential tremor specifically as "an isolated action tremor present in bilateral upper extremities for at least three years." 3
Clinical Presentation Beyond the Upper Extremities
While bilateral upper extremity involvement is required, tremor may extend to other body regions:
Tremor may also affect the head, neck, voice, legs, feet, trunk, jaw, chin, and tongue, though bilateral arm tremor remains the primary feature. 2, 3
Isolated head or voice tremor without bilateral arm involvement does not meet criteria for essential tremor. 1
Important Clinical Distinction
Unilateral tremor should prompt consideration of alternative diagnoses, particularly Parkinsonian syndromes, which often begin asymmetrically. 1
When clinical examination is equivocal, Ioflupane SPECT/CT can exclude Parkinsonian syndromes by demonstrating normal dopamine transporter uptake in the striatum. 1
Evolution of the Diagnostic Concept
The classification has evolved to include "essential tremor plus" for patients with bilateral action tremor who also exhibit additional neurological signs of unknown origin, such as cognitive impairment, psychiatric disorders, or gait abnormalities. 3, 4 However, the core bilateral tremor remains the defining feature.