Objective: To identify factors predictive of responsiveness of tremor to levodopa and STN-DBS.

Background: Tremor in Parkinson’s disease (PD) is phenotypically variable and has an inconsistent response to levodopa and subthalamic deep brain stimulation (STN-DBS). Understanding the reasons for this variability could potentially inform future surgical approaches to improve specific symptom outcomes.

Method: PD patients with upper limb tremor who underwent bilateral STN-DBS were included. The levodopa responsiveness of tremor (overall, postural and rest sub-components), appendicular and axial features was assessed using the relevant UPDRS III items performed during the pre-operative assessment by subtracting the ‘On’ and ‘Off’ medication scores. Post-surgical outcomes were assessed with the same items in the Off-medication condition, on and off stimulation. A score for the Rest/Postural tremor ratio was also determined at each visit to determine the relative influence of rest and postural tremor severity on STN-DBS outcome. Baseline factors predictive of tremor responsiveness to levodopa and STN-DBS were then determined using multiple linear regression modelling. Volume of tissue activated measurement coupled to voxel-based statistical analysis was then performed to identify anatomical clusters associated with greatest improvements in tremor and other parkinsonian features.

Results: 165 patients were included in this study. Male gender and the Rest/Postural tremor ratio were negatively correlated with tremor responsiveness to levodopa.

Levodopa responsiveness of the overall tremor score was not correlated with STN-DBS response of overall tremor score; however, the ratio of Rest/Postural tremor was positively associated with STN-DBS tremor outcome. Clusters corresponding to maximum improvement of tremor were in the subthalamic nucleus, the Zona Incerta and the thalamus while clusters corresponding to maximum improvement for akinesia and rigidity were mainly located within the supero-lateral part of the subthalamic nucleus.

Conclusion: The overall tremor responsiveness to levodopa did not predict tremor responsiveness to STN DBS. Combined more severe postural tremor and less severe rest tremor were associated with both poorer levodopa and STN-DBS response.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/tremor-characteristics-differentially-respond-to-levodopa-and-subthalamic-nucleus-deep-brain-stimulation-in-parkinsons-disease/