Objective Few studies have attempted to estimate the rate of decline over time in essential tremor (ET). The study objectives were to: (1) measure change, deriving a single summary measure for the entire group, and relate it to a commonly used clinical rating scale (ie, yearly change in points on that scale); (2) to assess change as a function of baseline clinical characteristics and (3) to answer the basic clinical question—is change perceptible/obvious during the follow-up of ET cases?

Setting Prospective collection of longitudinal data on ET cases enrolled in a study of the environmental epidemiology of ET at Columbia University Medical Center (2000–2008).

Participants 116 unselected ET cases.

Interventions Each case underwent the same evaluation at baseline and during one follow-up visit (mean follow-up interval (range)=5.8 (1.4–12.4) years).

Primary and secondary outcome measures We assessed tremor during a commonly affected daily activity—drawing (ie, spirography), quantifying tremor using a simple, standardised 10-point rating scale developed by Bain and Findley.

Results The Bain and Findley spiral score increased at an average rate of 0.12±0.23 points per year (maximum=1 point/year). In cases who had been followed for ≥5 years, the change was obvious—a blinded neurologist was able to correctly order their spirals (baseline vs follow-up) in three-fourth of cases. The rate of change was higher in cases with versus without familial ET (p=0.01).

Conclusions Tremor in ET is slowly progressive; yet in the majority of cases, a clear difference in handwritten spirals was visible with a follow-up interval of five or more years. There may be differences between familial and non-familial ET in the rate of progression. These clinical data are intended to aid in the prognostic discussions that treating physicians have with their patients with ET.