BACKGROUND: The Fahn-Tolosa-Marin Clinical Rating Scale for Tremor (FTM) has 
been used in large trials for essential tremor (ET), but its anchors for ratings 
from 0 to 4 of upper limb tremor are probably too low for patients with severe 
tremor (tremor amplitude >4 cm; grade 4). The Essential Tremor Rating Assessment 
Scale (TETRAS) is a validated clinical scale designed specifically for the 
assessment of ET severity. TETRAS has anchors that span a larger range of tremor 
amplitudes (>20 cm = grade 4), making it more suitable for assessing patients 
with severe ET. However, there is no direct comparison of these scales in any 
clinical trial.
METHODS: Upper limb postural and kinetic tremor items from both scales were 
compared using blinded, video-recorded examinations of patients with 
moderate-to-severe ET who participated in a trial of focused ultrasound 
thalamotomy.
RESULTS: FTM ratings of postural and kinetic tremor correlated strongly with 
those of TETRAS. However, FTM exhibited a ceiling effect for severe tremor. Rest 
tremor, exclusive to FTM, correlated poorly with postural and kinetic tremor and 
had very poor test-retest reliability. In contrast, wing-beating postural 
tremor, exclusive to TETRAS, exhibited excellent test-retest reliability and a 
strong correlation with kinetic and limbs-extended-forward postural tremor. 
Test-retest reliabilities of the other TETRAS and FTM ratings were excellent, 
and both scales had good sensitivity to treatment effect.
CONCLUSIONS: TETRAS has 2 main advantages over FTM in the assessment of tremor 
severity: (1) the absence of a ceiling effect in patients with severe ET, and 
(2) the inclusion of wing-beating tremor.