Objective: Establish methodologies, fast and easy to translate to clinics, that help discriminate between organic and functional dystonia.

Background: Functional dystonias are challenging diagnoses that are thought to be linked to psychological causes, although their pathophysiology remains unknown. There is a need to find reliable measurable differences between the two populations to support the difficult differential diagnosis.

Method: The techniques we used in this study with patients with established organic and functional dystonia were chosen because they have both potential to differentiate between the two populations based on literature, and are easy to translate to clinical use if they can discriminate between patients. We targeted the primary motor cortex (M1) and the cerebellum.To investigate excitability, inhibition and plasticity of M1 we used a fast alternative to the classical paired associative stimulation (PAS). PAS is a transcranial magnetic stimulation paradigm that repeatedly pairs a peripheral nerve stimulation with a TMS primary motor cortex (M1) pulse to induce hebbian-like plasticity. After confirming that a 2 minutes 5Hz protocol could induce a facilitation comparable to the classical 20 minutes 0.2Hz protocol in a cross-over study with healthy subject we used it to evaluate plasticity in patients.The eyeblink classical conditioning (EBCC), a well-documented form of cerebellar dependent learning paradigm, was used for non-invasive cerebellar activity investigation. In an effort to automate and ameliorate response detection, we used machine learning to automatically detect eyeblink in an unbiased and fast process.

Results: Patients with organic and functional dystonia all demonstrated significant altered M1 and cerebellar function in comparison to healthy age-matched volunteers. The number of patients with functional dystonia recruited is currently too low to process separately from patients with organic form. Analyses comparing the two populations will be included in the poster after further recordings.

Conclusion: PAS and EBCC are two promising clinical tools to help discriminate between organic and functional movement disorders. Both protocoles can be influenced by variables such as age or limb immobility, it is thus necessary to record enough patients to allow regression analysis and a definition of normal range of reponse considering all pertinent factors.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/defining-biomarkers-to-discriminate-between-organic-and-functional-dystonia/