Closed loop deep brain stimulation: A systematic scoping review

At the turn of the 21st century, closed-loop deep brain stimulation (CL-DBS) systems have emerged as promising neuromodulatory treatment strategies, that integrate real-time feedback based on the brain's condition to fine-tune the stimulation being applied. CL-DBS promises numerous advantages over open-loop deep brain stimulation (OL-DBS) systems. However, no up-to-date review articles are available which characterise the clinical outcomes of CL-DBS therapy.A systematic literature search was conducted in seven major databases with various keywords relating to CL-DBS, for non-randomised cohort studies, finalised clinical trials, case reports, and nonrandomised control trials published between 2011 and 2021.Seven studies satisfied our inclusion criteria. Six investigated the use of CL-DBS therapy for neurological disorders, while one investigated its use for psychiatric disorders. The average patient age was 61 years (range: 27 - 78), and the mean disease duration before CL-DBS therapy was 15 years (range: 4 - 47). Patients included with essential tremor (ET) (n = 11) were older than patients with freezing of gait (FoG) in Parkinson's disease (PD) (n = 6) (p = 0.009), albeit insignificantly longer disease duration (p = 0.199). Following CL-DBS intervention, patients with ET (n = 11), major depressive disorder (n = 1) and Tourette syndrome (n = 1) had improvements in clinical outcomes, while PD patients had heterogeneous outcomes (n = 7). CL-DBS systems utilised by the included studies demonstrated a mean of 51.94 % (range: 36.62 - 68) energy-saving capacity over OL-DBS systems.To date, there is insufficient evidence that CL-DBS offers significant superior clinical outcomes over OL-DBS. Our scoping review suggests that CL-DBS can improve symptoms of specific neurological and psychiatric disorders, whilst demonstrating improved energy-saving capacity which has the potential to decrease battery replacement surgeries. Real-time adjustment of patients' symptoms using CL-DBS may improve patients' overall quality of life. Further studies are required to validate our observations.