Community-based data on associations of disease duration and age with severity of essential tremor: Implications for disease pathophysiology

The pathophysiology of essential tremor (ET) is not well understood, although the tremor often worsens over time. Several processes could contribute, including the inherent worsening of the underlying disease with increasing disease duration and the effects of aging on the nervous system. Our objective was to examine the associations of disease duration and age with tremor severity in ET. Cases were ascertained from a community-based study of ET in northern Manhattan, New York. A neurologist rated tremor severity using a clinical rating scale and assigned a total tremor score (0-36 [maximum]). Analyses were repeated in a sample of cases from a tertiary referral center, the Neurological Institute of New York. There were 55 cases from the community-based study (mean age, 72.1 years, mean disease duration, 13.2 years). Disease duration was associated with the total tremor score (r = 0.30; P = 0.02). Age was associated with the total tremor score (r = 0.30; P = 0.025). In a linear regression analysis the dependent variable was the total tremor score and independent variables were disease duration, age, and gender. Duration (β = 0.11; P = 0.02) and age (β = 0. 10; P = 0.02) were independently associated with the total tremor score. Results were similar in 79 ET cases from the Neurological Institute. Disease duration and age were independently associated with tremor severity in ET. This suggests that the reported increase in tremor severity may be related to the inherent worsening of the disease with increasing duration, and that this is independent of age and age-related processes like neuronal attrition and change in tremor frequency.