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Abnormal Blink Reflex and Intermuscular Coherence in Writer's Cramp

Lookup NU author(s): Dr Supriyo Choudhury, Professor Mark BakerORCiD, Professor Stuart BakerORCiD

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Abstract

Background: Writer’s cramp (WC) is a task-specific focal hand dystonia presenting with pain, stiffness and/or tremor while writing. We explored the involvement of cortical and brainstem circuits by measuring intermuscular coherence (IMC) and pre-pulse inhibition of the blink reflex. Methods: IMC was measured in 10 healthy controls, 20 WC patients (10 with associated tremor) while they performed a precision grip task at different force levels. Blink responses were evaluated in 9 healthy controls and 10 WC patients by stimulating the right supraorbital nerve and recording surface EMG from the orbicularis oculi muscles bilaterally. Pre-pulse inhibition involved conditioning this stimulation with a prior shock to the right median nerve (100ms interval), and measuring the reduction in the R2 component of the blink reflex. Results: Significant IMC at 3-7Hz was present in WC patients, but not in healthy controls. Compared to healthy controls, in WC patients the R2 component of the blink reflex showed significantly less pre-pulse inhibition. IMC at 3-7 Hz could reliably discriminate WC patients from healthy controls.Conclusion: Cortical or sub-cortical circuits generating theta (3-7Hz) oscillations might play an important role in the pathogenesis of WC. Moreover, the lack of pre-pulse inhibition implicates abnormalities in brainstem inhibition in the emergence of WC. IMC may merit further development as an electrodiagnostic test for focal dystonia.

Publication metadata

Author(s): Choudhury S, Singh R, Chatterjee P, Trivedi S, Shubham S, Baker MR, Kumar H, Baker SN

Publication type: Article

Publication status: Published

Journal: Frontiers in Neurology

Year: 2018

Volume: 9

Online publication date: 02/07/2018

Acceptance date: 11/06/2018

Date deposited: 19/06/2018

ISSN (electronic): 1664-2295

Publisher: Frontiers Research Foundation

URL: https://doi.org/10.3389/fneur.2018.00517

DOI: 10.3389/fneur.2018.00517

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