Objective: Retrospective study whose main objectives is to describe the characteristics of Archimedes spiral (AS) (presence of axis and direction) and to relate them to different clinical diagnoses of tremor.

Background: The AS is part of Fahn-Tolosa-Marin (FTM) scale and is used to evaluate the severity of tremor in upper limbs. Some studies have considered the assessment of its features, such as the axis of the spiral, potentially useful to distinguish between Essential Tremor (ET) and Parkinson’s Disease (PD).

Method: A retrospective descriptive study of a consecutive case series of 143 patients with tremor in upper limbs assessed in movement disorders unit between February 2020 and May 2021 in a Movement Disorders Unit. A total of 286 large spirals were studied. The presence of axis and its direction were examined independently by two researchers, who were blinded to the etiological diagnosis. A third researcher with clinical expertise in movement disorders performed the clinical examination and classified patients with tremor according to MDS consensus tremor classification of 2018.

Results: The mean age was 71 ± 15 years. The diagnoses were: 30 ET, 25 ET plus, 65 PD, 12 ET and PD, 11 other diagnoses. Evaluation of the spiral axis and its direction showed a degree of concordance of 87.1% among evaluators. 55.9% of patients with ET had an axis in spiral and it was typical in 93% (maximum amplitude of oscillations in quadrants C1-C3). 46.9% of patients with ET-plus had an axis (typical in 87.5% of cases). 16.1% of patients with PD had an axis (typical in 95% of cases). 41.6% with ETs and PD had axis (typical in 100%).

Conclusion: AS is a simple and useful diagnostic tool for study of tremor and its interpretation is highly reproducible. Axis in AS was observed more frequently in patients with ET, ET plus and ET with PD than in those with PD alone. The pattern of spiral axis defined as typical was by far the most frequent, regardless of the aetiology of tremor. In contrast to other published case series with fewer patients, our series did not show a difference in the spiral axis between patients with essential tremor and those with Parkinson’s disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/value-of-archimedes-spiral-in-tremor/