The TETRAS was a validated clinical scale for the assessment of essential tremor severity. The TETRAS performance subscale was utilized by the qualified investigators to assess the tremor severity. TETRAS performance subscale consisted of 9 items: head, face, and voice tremor (items 1-3), UL tremor of right and left UL (item 4) in three tasks (forward outstretched postural tremor, lateral "wing-beating" postural tremor, kinetic tremor), Archimedes spirals with both hands, handwriting with motor-dominant hand, and dot approximation task with both hands (items 6-8), and lower limb tremor and standing tremor (items 5 and 9). Each item was rated from 0 (no tremor) to 4 (severe tremor) with overall performance score of 0 to 64, calculated as the sum of subscale items. Higher scores indicated greater tremor severity.