Long-term effect of bilateral STN-DBS on non-motor symptoms in Parkinson's disease: A four-year observational, prospective study

Background: Several studies have shown beneficial effects of bilateral stimulation of the subthalamic nucleus (STN-DBS) on motor as well as on non-motor symptoms (NMS) up to 36 months post-surgery in advanced Parkinson's disease (PD) patients. We set to explore the long-term effect of STN-DBS on NMS in a four-year follow-up, prospective, observational study.

Methods: Forty patients were enrolled and assessed at baseline. Twenty-eight were followed-up at 6, 12, 24, 36 and 48 months after the operation. The effect of post-operative time on NMS was analyzed by six-level repeated measures ANOVA. In a post-hoc analysis the follow-up scores were compared to baseline using a paired t-test.

Results: The following scores stayed improved up to 24 months after surgery, presented as baseline/24 months, p-value (t-test): total Non-Motor Symptoms Scale score (54.0 ± 5.6/44.9 ± 5.0, p = 0.029), Hamilton Anxiety Scale (14.3 ± 1.3/11.3 ± 1.2, p = 0.019) and PDQ39 (53.4 ± 4.5/40.2 ± 2.9, p = 0.012). PD Sleep Scale 2 remained improved throughout the study (17.4 ± 2.0/12.8 ± 1.3 at 48 months, p = 0.032), while Beck Depression Inventory only at six months post-surgery (9.5 ± 1.2/6.7 ± 0.7 at 6 months, p = 0.006). Montreal Cognitive Assessment remained stable up to 24 months and then declined at 36 months (26.3 ± 0.5/25.4 ± 0.5 at 36 months, p = 0.003), Starkstein Apathy Scale deteriorated throughout the study (7.6 ± 0.7/12.7 ± 0.9 at 48 months, p = 0.006).

Conclusions: We observed beneficial effect of STN-DBS in several but not all domains of NMS at least up to 24 months post-op in advanced PD. Further long-term studies on larger cohorts of PD patients and longer follow-up need to be conducted to better understand the long-term effect of STN-DBS on NMS.