Utility of the hand-drawn spiral as a tool in clinical-epidemiological research on essential tremor: Data from four essential tremor cohorts

Background: In descriptive epidemiological studies, investigators must screen large numbers of individuals. How one best screens populations for essential tremor (ET); however, remains an open question. The collection of a standardized writing sample (e.g., a hand-drawn spiral) is a method with many practical advantages, yet there are virtually no data on the validity of this particular method. Methods: Four hand-drawn spirals (2 right, 2 left) were collected from 831 ET cases across four distinct study settings (population-based study, family study, environmental epidemiological study, brain repository) and, in two of these studies, from 697 controls. Spirals were rated (range 0-3) by a senior movement disorder neurologist. These 1,528 participants also underwent a detailed neurological examination, and total tremor scores (range 0-36) and ET diagnoses were assigned by the neurologist. Results: The proportion of cases with hand-drawn spiral ratings ≥1.5 in either arm ranged from 78.8-97.0%; only 4.7% of controls had spirals with tremor of that severity. The hand-drawn spiral rating was highly correlated with the total tremor score (r = 0.65-0.73, p < 0.001). Conclusions: The hand-drawn spiral is a sensitive and specific method of screening for ET. Furthermore, it serves as a valid measure of overall tremor severity.