The aim of the study is to characterize the neuroinflammatory effects of subthalamic deep brain stimulation in patients with Parkinson's disease, by analyzing changes in blood neuroinflammatory and neurodegenerative biomarkers before and after surgery (at 6 and 12 months, respectively), and comparing the changes in blood biomarkers levels with a control group of patients with advanced PD on best medical treatment.

Inclusion Criteria:

• clinically established diagnosis of PD according to the criteria of the Movement Disorder Society (MDS) (Postuma et al., Mov Disord 2015);
• a minimum disease duration of 4 years;
• eligibility for STN-DBS surgery according to Core Assessment Program for Surgical Interventional Therapies in PD (Defer et al., Mov Disord 1999);
• age between 18 and 75 years.

Exclusion Criteria:

• inability to express an informed consent;
• moderate or severe cognitive impairment (score < 24 on the Mini-Mental State Examination);
• severe psychiatric symptoms (e.g., psychosis, major depression);
• previous neurosurgical interventions for PD;
• pregnancy;
• ongoing inflammatory or autoimmune diseases;
• chronic infectious diseases;
• active neoplasms;
• chronic intake of anti-inflammatory drugs (e.g. steroids or NSAIDs).

Among patients attending outpatient clinics for Movement Disorders, 45 subjects with advanced PD candidate for STN-DBS surgery (according to common clinical practice) and 45 subjects with advanced PD on best medical treatment, potentially eligible for DBS but who refused this therapy, will be enrolled.