Long-term quality of life trend after subthalamic stimulation for Parkinson's disease: An updated systematic review and meta-analysis

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Deep brain stimulation of the subthalamic nucleus (STN-DBS) is an effective treatment for Parkinson’s disease, and it has documented long-term benefits for the motor complications of the disease, lasting up to approximately 10 years. However, improvements in motor function do not necessarily lead to a better quality of life (QoL). This is because non-motor symptoms and psychosocial factors are also significant. For this reason, the long-term effects on quality of life are of extreme importance.  

The PDQ-39 is the most widely used tool for assessing the quality of life in individuals with Parkinson's disease. It comprises eight domains and a total of 39 questions. This questionnaire can be used to compute an index ranging from 0 to 100. Higher ratings indicate a lower quality of life. 

To our knowledge, no meta-analysis has systematically evaluated all eight PDQ domains after DBS surgery. This is important for identifying necessary future interventions to maintain QoL improvement over time. Therefore, we aimed to perform an updated systematic review and meta-analysis to accurately identify QoL trends up to five years after bilateral STN-DBS, and analyze its components and the influence of clinical and sociodemographic factors on QoL results. 

We identified 4,106 reports in the initial database search. Of these, a total of 42 studies and 2,767 patients were included in the final analysis. We show the mean difference in PDQ-39 scores compared to preoperative values. For example, at 12 months, there was an average improvement of 11.8 points on the scale. This improvement was not only statistically significant at 12, 24, and 36 months, but also clinically relevant, given that a threshold of 4.72 has been previously established in an extensive study as the minimal clinically important difference (MCID) for this scale  —that is, the slightest change in an outcome that a clinician or patient would consider meaningful and essential. However, by 60 months, the scores returned to their preoperative level. 

We also performed meta-regression analyses at different follow-up points, which revealed no significant associations between quality-of-life outcomes and most clinical factors, including mean disease duration, mean age at surgery, and sex. 

Although our analysis revealed moderate-to-high heterogeneity of 45%, PDQ-39 scores tend to return to preoperative levels within five years. The progression of non-motor symptoms over time due to the progression of the disease, as well as the development of axial problems that do not respond to L-DOPA or stimulation, become important determinants of long-term quality of life. These factors may explain the observed trend of returning to baseline levels of quality of life over time. The main limitation of our study is the absence of a control group receiving optimized medical therapy in the included studies. We conclude that it is essential to monitor quality of life between 36 and 60 months after subthalamic DBS. 

Currently, there are no established criteria for identifying candidates who are more likely to experience sustained improvements in quality of life after DBS surgery. Further studies can help doctors provide more personalized care. 

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