Objective: To investigate ipsilateral sensorimotor effects of thalamic deep brain stimulation (DBS).

Background: DBS at the border of the ventrointermediate thalamus (VIM) and the subthalamic area (STA) improves contralateral essential tremor (ET) resistant to medical treatment [1]. Ipsilateral effects on tremor are less well understood despite known ipsilateral anatomical connections along the dentato-rubro-thalamic tract [2].

Method: We report the case of a 77 year old woman who underwent DBS for ET in the left VIM /STA (5 months after DBS implantation, no tremor medication, St. Jude Infinity). An unilateral operation was undertaken because of lateralized tremor and higher perioperative risk due to age and comorbidities. Coordinates of the active contact of the DBS electrode were x=11.67 mm lateral, y = 6.27 mm posterior and z = -0.69 mm inferior in relation to the midcommisural point of the AC-PC-line. Stimulation parameters were 3 (ABC)- C+, 2.1 mA, 60 µs, 130 Hz.   We evaluated tremor severity by generating a sum score of the Fahn-Tolosa-Marin-Tremor-Rating-Scale (FTMTRS) for each side in the stimulation ON- and OFF-condition (items 5/6 for rest / posture / action tremor and item 14 for pouring a glass of water).

Results: As expected, tremor of the right side was strongly suppressed by contralateral DBS (OFF: 9, ON: 1). Only mild preoperative tremor on the left side was increased by ipsilateral DBS (OFF: 2, ON: 5). In particular, pouring a glass of water was worse (OFF: 1, ON: 3).

Conclusion: Ipsilateral effects of VIM / STA DBS are not well characterized yet and need further investigations. We suggest that ipsilateral worsening of tremor should be taken into account as possible adverse effect in patients with unilateral VIM/STA-DBS.

References: [1] Benabid AL, Pollak P, Gervason C, Hoffmann D, Gao DM, Hommel M, et al. Long-term suppression of tremor by chronic stimulation of the ventral intermediate thalamic nucleus. Lancet (London, England). 1991;337:403–6. [2] Meola A, Comert A, Yeh F-C, Sivakanthan S, Fernandez-Miranda JC. The nondecussating pathway of the dentatorubrothalamic tract in humans: human connectome-based tractographic study and microdissection validation. J. Neurosurg. 2016;124:1406–12.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/ipsilateral-worsening-of-essential-tremor-by-thalamic-deep-brain-stimulation/