Intention Tremor Severity Trajectory: Results from a Prospective Longitudinal Study of Essential Tremor

Patients with essential tremor (ET) may exhibit intention tremor (IT), a sign of cerebellar dysfunction. The prevalence of this sign has been established in cross-sectional studies. To date, however, there have been no cohort studies, re-assessing ET cases prospectively, to determine whether the severity of IT increases over time. The fundamental question is whether IT is progressive in ET.

90 cases enrolled in a prospective, longitudinal study of elders with ET. IT was assessed in each arm during the finger-nose-finger maneuver (10 repetitions per arm) and scored by a movement disorders neurologist on a 3-item scale - 0 (absent), 0.5 (probable), or 1 (definite), with the IT score (sum of IT in both arms) ranging from 0 - 2. Data from four evaluations every 18 months (T1 - T4) over a 4.5-year period were analyzed.

A one-way repeated measures analysis of variance revealed a time effect for IT, indicating significant variance across time in this variable. Paired sample t-tests indicated that the mean IT score at T4 was greater than those at T1, T2 and T3. There was heterogeneity in the sample, with the T4 score being greater than the T1 score in 46 (51.1%) of 90, but not all individuals.

The cerebellar sign, IT, progressively worsened over time in ET. To our knowledge, this is the first demonstration that any canonical cerebellar sign gets progressively worse during prospective follow-up of ET. This clinical observation serves to further the links between ET and progressive cerebellar decline.