Objective: To evaluate the efficacy of stimulation near the DRT on OT, based on standing time and QoL, and relate the proximity of stimulation to the ML and PT to side-effects.

Background: Primary orthostatic tremor (OT) is a rare hyperkinetic movement disorder that can severely influence quality of life (QoL). Treatment of OT with deep brain stimulation (DBS) was described by several groups but the number of published cases is limited and clinical effect, and underlying mechanisms, of DBS for OT is uncertain. It has been hypothesized that stimulation of the dentatorubrothalamic tract (DRT) is beneficial, whilst stimulation of the medial lemniscus (ML) and pyramidal tract (PT) are related to side-effects.

Method: Nine severely affected OT-patients received bilateral DBS. Clinical outcome measures included standing time, neurophysiological measures, QoL, surgical complications, and stimulation-induced side-effects. Data was extracted from EMG analyses, self-report scales, and the medical charts. Location of the active DBS electrode contacts in relation to the white matter tracts was also evaluated.

Results: Maximum standing time increased significantly in seven of nine patients, which was maintained at long-term follow-up (56 months). Two of the nine patients experienced no net positive effect and switched the DBS off. QoL increased during long-term follow-up, but remained below age-related normal values. None of the patients experienced surgical complications. However, all patients experienced one or multiple stimulation-induced side-effects, including dysarthria and balance problems, which persisted in varying degrees during follow-up despite adjustments in DBS settings. Analysis of volume of tissue activated after tractography in seven patients suggested stimulation of the DRT in six patients and simultaneous encroachment of the ML and/or PT by the stimulation in four patients.

Conclusion: DRT-DBS can lead to a prolonged improved maximum standing time and QoL. However, the improved maximum standing time and QoL varied between patients, possibly related to variations in DBS localization, side-effects, and expectations of patients. Tremor-effect can be related to stimulation of the DRT, while observed side-effects can be related to stimulation of the ML and PT. Although effect varied between patients, in the majority of the patients, DBS was of benefit and they were very satisfied.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/deep-brain-stimulation-for-orthostatic-tremor-an-observational-study/