Objective: In patients with primary orthostatic tremor (OT), we assessed how functional impairment, electrophysiological measures of tremor and long-range connection between the cerebellum and the motor areas could benefit from repetitive transcranial magnetic stimulation (rTMS) applied over the cerebellum during several consecutive days.

Background: OT is defined as a high frequency 13-18 Hz tremor affecting legs and trunk during the standing position. We showed recently structural abnormalities in the cerebellum and in the supplementary motor area (SMA) of OT patients. Essential tremor associated with cerebellar dysfunction could be improved by repetitive transcranial magnetic stimulation applied over the cerebellum for several consecutive days (Popa et al 2013). We tested here whether tremor severity in OT was also improved by cerebellar stimulation.

Methods: We used resting-state fMRI at 3 Tesla to compare 9 OT patients before (baseline) and after five consecutive days of cerebellar rTMS. We measured the cerebellar resting state (intrinsic) connectivity with primary and secondary motor areas. Degree of postural instability was assessed by the scores at the Fullerton Advanced Balance scale and duration of the possible standing position at baseline and 5, 12 and 26 days after the beginning of cerebellar rTMS treatment. Tremor was quantified from electromyographic recordings done in the standing position in time lines.

Results: Relative to baseline, OT patients’ cerebellum exhibited (i) a progressive decrease of the amplitude of the tremor frequency peak from day 5 to day 26; (ii) a decrease of intrinsic connectivity between the cerebellar lobule VI and the SMA at day 5. Instrinsic connectivity between the cerebellar lobule VI and the SMA correlated positively with the amplitude of the frequency peak at baseline. However, intrinsic connectivity between the cerebellar lobule VI and the SMA at day 5 correlated negatively with the amplitude of the frequency peak at day 26. Subjective postural instability remained the same.

Conclusions: The communication between the cerebellar lobules VI and the SMA has some functional relevance to the OT pathology… Secondary to cerebellar impairment, erroneous inputs from cerebellar lobule VI may reach the SMA at baseline. Cerebellar stimulation might counteract – at least partly- the abnormal communication.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/an-open-label-trial-to-test-the-modulation-of-cerebellar-motor-pathways-in-primary-orthostatic-tremor-using-rtms-and-fmri/