Objective: To evaluate the role of the cerebellum in tremor-dominant cervical dystonia (CD) using a standardized saccade adaptation task.

Background: While basal ganglia has long been hypothesized as the major pathophysiologic source of dystonia, there is also evidence for cerebellar dysfunction. A clinically distinct form of CD with prominent head tremor at onset and greater burden of disability for truncal ataxia than dystonia has been reported, indicating cerebellar involvement.

Method: Twelve subjects with tremor-dominant CD were compared with that collected from six healthy subjects. Subjects sat in a dark room in a stationary chair with their head stabilized. A high-resolution video oculography technique (EyeLink II, SR-Research, Mississauga, ON) was used to record horizontal and vertical eye positions. The eye positions were calibrated prior to initiation of the experiment using previously published techniques. Each subject underwent three sessions – initial open-loop trial, motor adaptation trial, and last open-loop trial. Open-loop trials assessed changes in saccade gain as an index of the level of adaptation. Motor adaptation trials involved six learning blocks, each consisting of 30 double-step saccade-adaptation trials.

Results: Tremor-dominant CD subjects were consistently unable to modify their saccade amplitudes during gain-increasing saccade adaptation paradigm. In healthy subjects, saccade amplitude got larger with the same paradigm. Further, CD subjects do not demonstrate saccade adaptation at slow or fast timescale.

Conclusion: Our investigation reveals impaired saccade adaptation on slow and fast timescales suggesting maladaptive cerebellar output in tremor-dominant CD subjects.

References: 1. Batla A, Sanchez MC, Erro R, et al. The role of cerebellum in patients with late onset cervical/segmental dystonia?–evidence from the clinic. Parkinsonism Relat Disord 2015;21(11):1317-1322. 2. Merola A, Dwivedi AK, Shaikh AG, et al. Head tremor at disease onset: an ataxic phenotype of cervical dystonia. J Neurol 2019;266(8):1844-1851. 3. Shaikh AG, Ghasia FF. Misdirected horizontal saccades in pan-cerebellar atrophy. J Neurol Sci 2015;355(1-2):125-130. 4. Fujita M, Amagai A, Minakawa F, Aoki M. Selective and delay adaptation of human saccades. Brain Res Cogn Brain Res 2002;13(1):41-52.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/tremor-dominant-cervical-dystonia-and-the-cerebellum-lessons-from-saccade-adaptation/