Long-term follow-up of subthalamic nucleus deep brain stimulation in patients with Parkinson’s disease: an analysis of survival and disability milestones

Background Data on the long-term survival and incidence of disability milestones after subthalamic nucleus deep brain stimulation (STN-DBS) in Parkinson’s disease (PD) is limited. Objectives To estimate mortality among PD patients 8 years after STN-DBS and to quantify the frequency /time-to-development of disability milestones (falls, freezing, hallucinations, dementia, and institutionalization). Methods A longitudinal retrospective study of patients submitted to STN-DBS between 2006-2012 was carried-out. For mortality, Cox proportional hazards regression analysis was performed. For disease milestones, competing risk analyses were performed and cumulative incidence functions calculated. Multivariable regression analysis in the presence of competing risks was performed based on the Gray’s test of sub-distribution hazards of cumulative incidence functions. Results An overall mortality rate of 16% (mean 62.1 ± 21.3 months after surgery) was observed. Falls (73%) and freezing (47%) were both the earliest (40.4 ± 25.4 and 39.6 ± 28.4 months, respectively) and most frequently observed milestones. Dementia (34%) and hallucinations (32%) soon follow (56.2 ± 21.2 and mean 60.0 ± 20.7 months after surgery, respectively). Institutionalization occurred in 6% after 62.3 ± 22.0 months. Higher ADL scores in the OFF state and higher age at surgery were associated with falls, freezing, dementia and institutionalization. Conclusions Long-term mortality rate is low after STN-DBS, with STN-DBS patients developing the same disability milestones as non-DBS patients. Motor milestones occur first and at a higher frequency than cognitive ones. Milestones cluster together before death.