Objective: To highlight the predictors for onset of cerebellar ataxia in patients treated with deep brain stimulation (DBS) of the Thalamic Ventral Intermediate Nucleus (VIM) for pharmacoresistant tremor, via a series of four cases treated by VIM DBS for essential tremor (ET) and review of the literature.

Background: Cerebellar ataxia is a late disabling complication following VIM DBS stimulation, affecting up to 35% of patients. Little is known about risk factors and delay of ataxia development. Identifying risk factors would aid in patient selection. The few existing publications indicate older age, preexisting ataxia and shorter tremor duration. Data on the delay of onset of ataxia is discordant: between a few months to 5.5 years.

Method: We present a descriptive case series of four patients from our database treated with VIM DBS for pharmacoresistant ET that developed cerebellar ataxia during follow-up. For each patient, we collected demographic data, pre-stimulation health conditions, date of surgery, DBS parameters and delay of onset of ataxia as well as reprogramming strategies. We commented the possible presence of ataxia risk factors considering data of the literature.

Results: The age range was 50 to 63 years at the time of surgery, with a median of 55 years. Patients benefited from DBS 15 to 31 years after the onset of tremor (median 21.5 years), without preceding ataxia. Out of the four patients, three developed signs of tolerance to DBS, needing progressive increase of the stimulation parameters. Ataxia appeared 2 to 6 years (median 3.5 years) after DBS.  Stimulation settings were monopolar for all patients, with a pulse width of 60 µs, amplitude varied from 2 to 3.5 V (median 3.1 V), frequency from 130 to 185 Hz. All of the patients had multiple sessions of reprogramming. In contrast with acute DBS induced ataxia, when switching off the stimulation, ataxia persisted and all patients had severe tremor rebound. For only one of the four patients, change in stimulation setting resulted in regression of the ataxia.

Conclusion: We present four patients treated with VIM DBS for pharmacoresistant ET who developed late cerebellar ataxia. In contrast to what was described before, they were relatively young, had essential tremor for a long period, and moderate amplitudes. It would be interesting to conduct a comparative study to better identify risk factors for cerebellar ataxia.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/late-onset-cerebellar-ataxia-in-patients-treated-with-vim-dbs/