Shaky drawing: what is the rate of decline during prospective follow-up of essential tremor?

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.