Objective: To investigate the long-term efficacy of unilateral deep brain stimulation and the progression of motor symptoms on the untreated side in Parkinson’s disease (PD) patients, emphasizing the potential need for bilateral stimulation.

Background: DBS of the subthalamic nucleus or ventral intermediate nucleus is an effective treatment for motor symptoms in PD. While many patients undergo bilateral DBS, some initially present with predominantly unilateral motor symptoms and receive unilateral DBS. However, the untreated side may eventually exhibit symptom progression, necessitating bilateral stimulation.

Method: We retrospectively analyzed data from 11 PD patients who received left-sided DBS due to predominantly right-sided motor symptoms at baseline (10 STN, 1 VIM). Motor symptom severity was assessed using the Movement Disorder Society-Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) at various time points: pre-DBS off and on medication, 6 months post-DBS, 1 year post-DBS, and 2 years post-DBS. Hemibody scores were also evaluated.

Results: At baseline, the mean pre-DBS off-medication total MDS-UPDRS score was 29.8, and the on-medication score was 20.7. After left-sided DBS, the mean total MDS-UPDRS scores on medication were 13.7, 15.6, and 27.0 at 6 months, 1 year, and 2 years, respectively. Focusing on hemibody scores, the mean pre-DBS right hemibody MDS-UPDRS score was 19.5 off medication and 9.5 on medication, improving to 3.74, 3.3, and 4.5 at 6 months, 1 year, and 2 years post-DBS, respectively. In contrast, the mean pre-DBS left hemibody MDS-UPDRS score was 5.6 off medication and 3.2 on medication, worsening to 4.3, 5.0, and 12.5 at the same time points. Four out of 11 patients (36.4%) required right-sided DBS surgery within 30-62 months (mean 40.5 months) after the initial left-sided implantation.

Conclusion: Unilateral DBS effectively improves contralateral motor symptoms in PD patients. However, untreated hemibodies exhibited a progressive increase in symptom severity over time, with over one-third of patients requiring contralateral deep brain stimulation within 4 years of the initial surgery. These findings emphasize the importance of considering bilateral treatment to prevent unilateral symptom exacerbation. Future research should explore neuroimaging and other biomarkers to identify patients at risk of rapid symptom progression who may benefit from earlier bilateral DBS.

Hemibody MDS-UPDRS scores

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MDS Abstracts - https://www.mdsabstracts.org/abstract/unilateral-deep-brain-stimulation-in-parkinsons-disease-long-term-efficacy-and-bilateral-symptom-progression/