Spirography Potential Predictor for Tremor Severity
In a recent study, 23 subjects diagnosed with essential tremor (ET) were asked to draw one Archimedes spiral with each hand. ET, one of the most prevalent movement disorders, commonly affects the hands. The drawing of the Archimedes Spiral is assessed as a diagnostic tool for ET. The results were analyzed to correlate tremor intensity measured via computerized tremor spirography with subjective tremor ratings of patients with ET. Details of the study were published by the National Institute of Neurological Disorders and Stroke (www.ninds.nih.gov).
The drawn spirals were collected on a tablet PC using self-developed software to record and analyze spirals (NeuroGlyphics). Tremor can be quantified using objective measures of tremor amplitude such as spiral analysis (spirography) and accelerometry, or by using clinical rating scales.
Subjects also subjectively rated specific tasks on the level of difficulty and impairment on their
daily life on a scale from 0 (no effect on everyday life) to 4 (task is not possible due to tremor),
according to the 12-item section on subjective impairment of The Essential Tremor Rating
Assessment Scale (TETRAS). The digitized spirals were analyzed, scored, and correlated to
the subjective total score as well as the 12 sub-items. Generated spiral scores were also
compared to the total score of the TETRAS performance scale.
Results indicate that both dominant and most affected hand computerized spiral scores correlated
significantly with the TETRAS performance rating. Computerized spiral scores of the dominant hand
significantly correlated with TETRAS ratings on impairment in daily life tasks, such as “carrying
trays,” “using keys” and “writing” as well as “feeding with a spoon” and “dressing.”
This correlation suggests that objective methods to quantify tremor can act as valid instruments
to predict how subjects rate the severity of their tremor. Spirals taken from the dominant hand
are better predictors than those from the hand which is most affected, because tasks such as
holding a glass, and handwriting are mainly performed with the dominant hand, regardless
whether the dominant hand is the more or less affected hand. This study demonstrates the validity
of ET spirography as a potential outcome measure for clinical trials reflecting not only objective
tremor ratings but also the subjective perception of tremor in patients with ET.