Objective: To investigate whether changes in Arquimedes’ spiral can be an objective test for bringing up the inconsistency in patients with functional overlay tremor

Background: There is a general agreement that functional disorders diagnosis should be based on positive signs to demonstrate the inconsistency and incongruence of these disorders.
However, in “functional overlay” patients, the diagnosis can be somewhat tricky, and the reliability of laboratory-supported criteria has not been properly assessed.

Method: Two patients with previous diagnose of essential tremor were studied.
After several years of stable tremor, they began with irregular tremor and additional symptoms considered unexplained by that disease.
Neurological examinations, including the Fahn-Tolosa-Marin scale, were performed, and a standard battery of tests for the diagnosis of functional disorders based on neurophysiological tests were investigated.

Results: Neurological examination did not reveal another different disease than  essential tremor in both patients. Neurophysiological test demonstrated signs of a functional disorder. Interestingly, a significant change in the Arquimedes´ spiral consisting of the previous axis’ loss was evident.

Conclusion: Loss of previous normal axis in Arquimedes’ spiral may be an objective data to demonstrate the inconsistency in patients with previous diagnosis of essential tremor who change their symptomatology.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/loss-of-spiral-axis-for-diagnoses-of-functional-tremor/