Effects of deep brain stimulation on non-motor symptoms in Parkinson's disease: insights from longitudinal studies...

Deep brain stimulation (DBS) is an effective treatment for motor symptoms in Parkinson's disease (PD). However, its effects on non-motor symptoms (NMS) have been rarely assessed due to inconsistencies in evaluation methods used in different studies. This meta-analysis aimed to assess the effects of DBS on NMS in PD using studies that employed consistent, standardized evaluation tools.

A systematic review was conducted following the PRISMA guidelines. Longitudinal studies published between 2007 and 2024 were included if they evaluated bilateral DBS using identical NMS scales with involvement of at least six studies per tool. Assessment tools included the Beck Depression Inventory (BDI and BDI-II), the Hamilton Depression Rating Scale (HAMD), the Apathy Evaluation Scale (AES), the Epworth Sleepiness Scale (ESS), Parkinson's Disease Sleep Scale (PDSS), the Non-Motor Symptoms Scale (NMSS), the Mini-Mental State Examination (MMSE), and the Parkinson's Disease Questionnaire-39 (PDQ-39).

Notably, 57 studies involving 3,200 patients were included. DBS significantly improved NMS, including depression (SMD:-0.19 to -0.35), sleep quality (PDSS SMD: 0.68; ESS SMD: - 0.32), and overall NMS (SMD: - 0.62). Moreover, quality-of-life was significantly improved (SMD: - 0.71), except in the communication domain. Although the levodopa equivalent daily dose (LEDD) was reduced by 49.2%, no significant correlation was found between LEDD reduction and quality-of-life improvement.

DBS could provide significant improvements in key NMS of PD, independent of reductions in LEDD. These findings revealed the direct neuromodulatory effects of DBS and highlighted its role in personalized treatment planning, particularly for patients with prominent depressive symptoms or sleep disturbances.