Objective: In this study, we aimed to determine changes in distribution of tremor dominant body side after DBS and searched for possible explanations if tremor dominant side changed to the other side.

Background: One of the supportive features for the diagnosis of idiopathic Parkinson’s disease (PD) is the asymmetrical distribution of motor symptoms such as tremors. Wrong-sided tremors have been described in patients with tremors on the body side ipsilateral to the side of the nigrostriatal dopaminergic deficit. While most motor symptoms in classical PD are levodopa responsive, tremor may be particularly therapy resistant. In such patients, deep brain stimulation (DBS) of the subthalamic nucleus (STN) and ventral intermediate nucleus of the thalamus is an effective and established treatment.

Methods: We retrospectively compared clinical tremor scores from 106 PD patients receiving DBS between 1999 and 2015 and classified patients into tremor-dominant (TD), postural instability and gait difficulty and a mixed phenotype subgroup. Tremor scores of UPDRS-III items 20 and 21 of left and right extremities were compared before and after DBS-implantation. The relative difference in tremor score between the symptom dominant and non-dominant side was calculated before and one year after DBS implantation.

Results: PD subtypes were identified in 71 patients. Tremor reduction one year after DBS implantation was strongest on the initial symptom dominant body side in all subgroups. In the TD subgroup there was a three-fold larger reduction of tremor scores on the dominant side compared to the non-dominant side (p<0.001). In 14% of patients, this difference in distribution of tremor reduction led to a change of the tremor dominant body side as compared to the pre-operative situation. All but one of these patients with side-changing tremor had a TD subtype and all but two received STN-DBS. In addition, this group had a higher age of disease onset and age during DBS implantation. Stimulation parameter surveys and total current amplitude differences between body sides did not explain post-operative asymmetry of tremor scores.

Conclusions: After STN-DBS, a change in tremor dominant body side is frequently observed which may be relevant for pre- and post-operative counseling of patients and should prompt clinicians to search for possible explanations.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/change-of-tremor-dominant-body-side-after-deep-brain-stimulation-in-patients-with-parkinsons-disease/