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

Abstract

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.