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Quantitative Separation of Tremor and Ataxia in Essential Tremor
Author(s) -
CasamentoMoran Agostina,
Yacoubi Basma,
Wilkes Bradley J.,
Hess Christopher W.,
Foote Kelly D.,
Okun Michael S.,
Wagle Shukla Aparna,
Vaillancourt David E.,
Christou Evangelos A.
Publication year - 2020
Publication title -
annals of neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.764
H-Index - 296
eISSN - 1531-8249
pISSN - 0364-5134
DOI - 10.1002/ana.25781
Subject(s) - dysmetria , essential tremor , intention tremor , ataxia , deep brain stimulation , psychology , physical medicine and rehabilitation , neuroscience , audiology , medicine , parkinson's disease , disease , pathology
Objective This study addresses an important problem in neurology, distinguishing tremor and ataxia using quantitative methods. Specifically, we aimed to quantitatively separate dysmetria, a cardinal sign of ataxia, from tremor in essential tremor (ET). Methods In Experiment 1, we compared 19 participants diagnosed with ET undergoing thalamic deep brain stimulation (DBS; ET DBS ) to 19 healthy controls (HC). We quantified tremor during postural tasks using accelerometry and dysmetria with fast, reverse‐at‐target goal‐directed movements. To ensure that endpoint accuracy was unaffected by tremor, we quantified dysmetria in selected trials manifesting a smooth trajectory to the endpoint. Finally, we manipulated tremor amplitude by switching DBS ON and OFF to examine its effect on dysmetria. In Experiment 2, we compared 10 ET participants with 10 HC to determine whether we could identify and distinguish dysmetria from tremor in non‐DBS ET. Results Three findings suggest that we can quantify dysmetria independently of tremor in ET. First, ET DBS and ET exhibited greater dysmetria than HC and dysmetria did not correlate with tremor ( R 2 < 0.01). Second, even for trials with tremor‐free trajectories to the target, ET exhibited greater dysmetria than HC ( p < 0.01). Third, activating DBS reduced tremor ( p < 0.01) but had no effect on dysmetria ( p > 0.2). Interpretation We demonstrate that dysmetria can be quantified independently of tremor using fast, reverse‐at‐target goal‐directed movements. These results have important implications for the understanding of ET and other cerebellar and tremor disorders. Future research should examine the neurophysiological mechanisms underlying each symptom and characterize their independent contribution to disability. ANN NEUROL 2020;88:375–387.