Deep brain stimulation linked to declining brain function in Parkinson’s patients

1. Patients that received deep brain stimulation (DBS) surgery demonstrated significantly greater decline in neuropsychological function within 6 months when compared to patients having received no surgery.

2. Of patients receiving DBS, 11% displayed multi-domain cognitive decline (MDCD), which was associated with a negative effect on patient quality of life.

Evidence Rating Level: 2 (Good)

Study Rundown: DBS, which involves the implantation of a small device into the brain that sends out electrical stimulation signals, has been shown to improve some aspects of Parkinson’s disease, including motor function and quality of life. The mechanisms behind DBS, however, remain unclear, and studies have shown DBS is also associated with a decline in neuropsychological, or brain function.

This study compared neuropsychological function in patients having received DBS and patients having received the best medical therapy excluding DBS (BMT). They found that DBS patients had an increased risk of decline in neuropsychological function, as determined by numerous measures of processing speed and working memory. Additionally, the number of patients exhibiting MDCD was significantly greater in the DBS group (11%) than in the BMT group (3%). This MDCD was associated with a negative effect on quality of life, and its effects remained at two-year follow up. Looking more closely at the DBS group, researchers investigated whether the location of the stimulation within the brain mattered. Only small variations in measures of brain function were found between the two brain locations considered, the subthalamic nucleus(STN) and the globus pallidus interna(GPI).

This study is limited by small sample size and incomplete reporting on patient dropout which, if corrected for, may have shown an even greater morbidity associated with DBS. This study provides important evidence of the potential negative ramifications of DBS, and suggests the need for a way to identify subgroups of patients that may be at particular risk for MDCD following DBS.

Click to read the study in Journal of Neurology, Neurosurgery, and Psychiatry

Relevant Reading: Cognitive declines one year after unilateral deep brain stimulation surgery in parkinson’s disease: A controlled study using reliable change

In-Depth [prospective, randomized trial]: This study compared brain function in 281 Parkinson’s patients, of which 117 received BMT and 163 received DBS. The DBS group was further divided into patients that received DBS at the STN (n = 84), or the GPI (n = 80). Patients underwent surgery within one month of assignment, in which stereotactic techniques with MRI or CT guidance were employed to reach target locations. A wide array of neuropsychological function testing was used to assess patient brain function at baseline and at 6 months post treatment. Patients with DBS were tested while stimulation was occurring. Rates of decline in cognitive function were evaluated in terms of reliable change.

Only 3 out of 25 tests showed a significant difference in neuropsychological function between the STN and GPI patient groups. Combining these two subgroups to form the total DBS patient group, researchers found significant difference between cognitive function at 6 months post procedure in DBS patients and BMT patients. Measurements of processing speed and working memory showed elevated rates of statistically reliable decline in DBS patients when compared to BMT patients. MDCD was found in 11% of DBS patients and only 3% of BMT patients (p = 0.024). DBS patients with MDCD demonstrated a significant decline in quality of life measurements (PDQ-39 assessment) at 6 and 24 months.

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