Objective: To report a case of an 81 year-old male with ventral intermediate nucleus (VIM) deep brain stimulation (DBS) for essential tremor (ET) who developed stimulation-related side-effects mimicking progressive supranuclear palsy (PSP).

Background: VIM DBS is a generally well-tolerated therapy for medically refractory ET. Side effects of stimulation can include changes in speech, gait, and cognition and are more likely to occur with higher voltages due to spread of current to surrounding structures.

Methods: An 81-year-old male with a fifteen-year history of ET underwent DBS surgery six years prior to presentation. Two electrodes targeting the left VIM were required in order to achieve intraoperative benefit for tremor. Two years prior, he developed parkinsonism in the setting of significant cognitive impairment, aphasia, and abnormal eye movements, including square wave jerks, saccadic pursuits, and slow and incomplete vertical and horizontal saccades. He underwent neuropsychological testing which suggested frontal-subcortical dysfunction, and he was tentatively diagnosed with PSP. He presented to our center for a second opinion and was noted to be non-ambulatory with marked inattention, decreased responsiveness and aphasia. Both left VIM electrodes were active with the following settings: Electrode A 1-2-C+ 5.0 V, 150 μs, 200 Hz; Electrode B 4-5-C+ 5.0 V, 120 μs, 200 Hz.

Results: After reducing the settings of electrode A and turning off electrode B, the patient had a dramatic improvement in his level of alertness, cognition, language, and gait, with normalization of eye movements. He was able to speak in full sentences and walk independently for the first time in many months. Though he remained Parkinsonian, immediate and dramatic resolution of many of his atypical symptoms suggested that the atypical features noted were due to his DBS settings. He has since remained ambulatory with a walker and has responded typically to levodopa therapy.

Conclusions: This case illustrates the importance of maintaining a high level of suspicion for stimulation induced side effects in patients with DBS. In this patient, evaluation without consideration of DBS settings led to an over-estimation of the degree of cognitive, language, and gait difficulties present and resulted in a misdiagnosis of PSP in a patient with ET who later developed superimposed Parkinson’s disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/high-voltage-stimulation-of-the-vim-thalamus-mimicking-psp-in-a-patient-with-et-pd/