Cognitive changes before DBS not a dementia risk factor in Parkinson’s
Study: Condition more likely in patients with longer disease duration
People with Parkinson’s disease who have mild cognitive changes before deep brain stimulation (DBS) are not more likely to develop dementia later in life than those whose cognitive function was normal before the surgery, a Danish study has found.
Instead, the researchers observed that dementia was more likely to develop among those who had been diagnosed with Parkinson’s for a longer duration at the time of the surgical procedure. This was found regardless of the patients’ ages, sex, or level of education.
“Disease duration, but not presurgical MCI [mild cognitive impairment] was associated with development of dementia,” the team wrote, noting that “influence on cognition” was detailed in “a short- and long-term follow-up study up to 15 years” following DBS surgery among patients.
Titled “Mild cognitive impairment is not predictive of dementia up to 15 years after subthalamic deep brain stimulation in Parkinson’s disease,” the study was published in the Journal of Parkinson’s Disease.
After DBS, verbal fluency, other cognitive skills seen to decline
In DBS, small electrodes are placed into deep areas of the brain. These electrodes are connected by thin wires to a device called a pulse generator, which sends mild electrical pulses to regulate brain activity and ease the motor symptoms that are a hallmark of Parkinson’s.
In addition to these symptoms, many people with Parkinson’s experience cognitive changes that often begin as mild cognitive impairment — small but noticeable problems with attention, planning, or memory beyond those of normal aging. When these problems become severe enough to interfere with daily life, doctors refer to it as dementia.
“Cognitive impairment and dementia are common in [the] later stages of Parkinson’s,” the researchers wrote. However, little is known about the long-term effects of DBS on cognition. Such a study, the team noted, “must take into consideration the progression of disease, as well as the background risk of dementia.”
To understand how DBS affects cognitive function in the long term, the researchers followed 81 patients who had been living with Parkinson’s for an average of 13 years. Half of them already exhibited signs of mild cognitive impairment before surgery, the data showed.
Three months after DBS, all of the patients showed significantly worse verbal fluency, indicated by how quickly they could name words in a certain category or words starting with a specific letter, or switch between types of words. Other cognitive skills also showed some decline, but the changes weren’t large enough to be considered significant.
Parkinson’s patients with depression more likely to develop dementia
A total of 29 patients were followed for up to 15 years. Among them, about two-thirds developed mild cognitive impairment or dementia. Six, or 21%, had signs of cognitive changes but no clinical diagnosis of dementia.
Four patients — all women — had normal cognitive function. On average, these four were younger at the time of surgery (47.4 years vs. 57.5 years) than the others in the study. They also had Parkinson’s for a shorter duration before surgery (8.5 years vs. 12 years).
No link was found between having mild cognitive impairment before surgery and later developing dementia. About 51% of those with early cognitive changes developed dementia, compared with 55% of those who had normal cognitive function before surgery, the data showed.
Disease duration and … depressive symptoms before surgery were associated with the later development of clinically diagnosed dementia.
However, living with Parkinson’s for a longer time before surgery was linked to a higher likelihood of developing dementia. For each additional year of living with the disease before surgery, the odds of developing dementia later increased by about 20%.
Before surgery, about a third of patients had symptoms of depression, which may occur as a nonmotor symptom of Parkinson’s and be linked to low cognitive function. Patients with symptoms of depression were more likely to develop dementia later, the study found.
“Disease duration and … depressive symptoms before surgery were associated with the later development of clinically diagnosed dementia,” the researchers wrote.
As a limitation of the study, the researchers noted the “relatively small” number of patients. This, as well as a lack of a control group, “[make] it difficult to draw a conclusion” on all data, the team wrote.
“The study is meant to be hypothesis-generating, and results should be further tested in other studies,” the researchers concluded.
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