Severity Stages in Essential Tremor: A Long-Term Retrospective Study Using the Glass Scale

BACKGROUND Few prospective studies have attempted to estimate the rate of decline of essential tremor (ET) and these were over a relatively short time period (less than 10 years). We performed a long-term study of severity stages in ET using the Glass Scale scoring system. METHODS Fifty consecutive patients with severe ET were included. We retrospectively obtained Glass Scale scores throughout the patient's life. Common milestone events were used to help recall changes in tremor severity. RESULTS According to the Glass Scale, the age distributions were as follows: score I, 40±17 years, score II, 55±12 years, score III, 64±9 years, and score IV, 69±7 years. A significant negative correlation between age at first symptom and rate of progression was found (r = -0.669, p<0.001). The rate of progression was significantly different (p<0.001) when the first symptom appeared at a younger age (under 40 years of age) compared with older age (40 years or older). DISCUSSION Our results support the progressive nature of ET. Age at onset was a prognostic factor. The Glass Scale may be a useful tool to determine severity stages during the course of ET in a manner similar to the Hoehn and Yahr Scale for Parkinson's disease.