**8. Conclusions**

Advances in understanding both the complexity of PD and the e ffect of DBS in PD patients have provided new evidence for a better stratification of patients and a more conscious use of this therapeutic option.

It is critical to take into account that the multifaceted symptomatology of PD, encompassing motor, non-motor, and behavioral issues, makes a candidate's selection for advanced therapies a process di fficult to fit in fixed and precise borders. Additionally, the probability of improving or worsening certain symptoms according to clinical trials (or to post-hoc analysis of trials) cannot capture the full clinical complexity and heterogeneity of the PD clinical spectrum and should be used cautiously for making a decision at a single level. To date, in addition to studies supporting a better comprehension of pre-surgical predictors of DBS outcomes, we also need a shift in the statistical approach to improve the decision-making from a group to an individual level.

In conclusion, the improvement in the stratification of PD patients according to their clinical features and genetic background can inform the disease course, and more-in-depth knowledge on patients most probable to benefit from DBS. A redefinition of CAPSIT-PD criteria for DBS should be pursued based on the new knowledge gained on PD clinical spectrum and DBS long term follow-up studies. This would allow surgical centers to be more accurate in predicting the outcome after functional neurosurgery and choosing the best target for stimulation. We can now estimate the probability to improve specific disabling symptoms and choose integrated approaches, combining stimulation of specific targets according to patients' issues (e.g., ventral STN for high non-motor burden [73]) with other therapeutic options (e.g., rehabilitation), with the ultimate goal of improving ADL, mental wellbeing, and eventually the QoL of PD patients. This viewpoint provided updated recommendations for a more accurate and fine-grained assessment of PD patients considered as potential candidates for DBS and highlighted the need for further studies to strengthen the evidence on predictors of DBS outcomes at an individual level, encompassing the complex and multifaceted syndromic picture of the disease and the new possibilities o ffered by validated clinical scales, technological devices, and genetic analysis.

**Author Contributions:** C.A.A.: conception, design and organization of the study, literature search, writing of the first draft; L.L.: data interpretation, review and critique; F.M.: conception, design and organization of the study, literature search, review and critique. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Financial Disclosures:** Carlo Alberto Artusi: received travel grants from Zambon and Abbvie, and educational grants from Ralpharma and Neuraxpharm. Leonardo Lopiano: speaking honoraria from UCB Pharma, AbbVie, DOC, Zambon and Bial. Francesca Morgante: speaking honoraria from Abbvie, Medtronic, Zambon, Bial, Merz; Travel grants from the International Parkinson's disease and Movement Disorder Society; advisory board fees from Merz; consultancy fees from Boston Scientific, Merz and Bial; research support from Boston Scientific, Merz and Global Kynetic; royalties for the book "Disorders of Movement" from Springer; member of the editorial board of Movement Disorders, Movement Disorders Clinical Practice, European Journal of Neurology.
