Objective: To compare the benefits of GPI and STN DBS on tremor in Parkinson’s disease (PD).

Background: DBS is a highly effective surgical therapy for the motor symptoms and motor complications in PD. There is a general preference to choose STN over GPI because of the claims of a superior benefit of STN DBS for tremor control in PD despite the lack of substantial evidence.

Method: 70 consecutive PD cases who underwent bilateral DBS (51 STN, 19 GPI), for motor fluctuations, dyskinesias or medically unresponsive tremor were included. GPI DBS was chosen when movement disorder specialist anticipated continued levodopa requirement for motor or non-motor symptoms post DBS or those with cognitive or behavioral impairment. All cases underwent uniform assessment. Pre-operative assessments were done in DRUG ON and OFF and post-operative assessments in STIMULATION ON-DRUG OFF states. Post op assessments were performed at 3months in GPI DBS group and at 6 months in the STN group so that drug reduction and adjustments were stabilized in STN group. Tremor score was measured using published methods as the sum of UPDRS II item 16 + UPDRS III items 20 and 21.¹ Effect of DBS on tremor between two groups was measured as percentage of change in scores between Pre-op Drug OFF and Post-op STIM ON-Drug OFF state. The total electrical energy delivered (TEED) at the assessment visit was calculated using the formula TEED = (voltage² x pulse width x frequency)/ impedance] and the average of both sides used for each subject.

Results: All cases completed the 3-month or 6-month follow up assessment. The median age of onset of disease was 51 years (range 46 – 56) in STN group and 54 years (range 51 – 59) in the GPI group (P = 0.06). The median age at surgery was 62 years (range 55 – 67) and 66 years (range 63 – 68) in STN and GPI groups respectively (P = 0.025). The disease duration was similar in both groups (P= 0.234). The baseline preoperative UPDRS scores in Drug OFF state were similar in both groups (Table 1). Both STN and GPI DBS improved Rest tremor, Action tremor scores to the same extent and Total UPDRS II + III tremor scores on short term follow up(P>0.05) (Table 2).

Conclusion: Both STN and GPI DBS were associated with good tremor outcomes in PD with no superiority of any one target. Target selection could be based on other favorable features of either of the target in any individual patient.

Table 1: Baseline characteristics before DBS

Tremor outcome STN Vs GPI DBS – percentage change

References: 1. Stebbins GT, Goetz CG, Burn DJ, Jankovic J, Khoo TK, Tilley BC. How to identify tremor dominant and postural instability/gait difficulty groups with the movement disorder society unified Parkinson’s disease rating scale: comparison with the unified Parkinson’s disease rating scale. Movement Disorders. 2013 May;28(5):668-70.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/is-gpi-dbs-as-effective-to-stn-dbs-for-tremor-control-in-parkinsons-disease/