The study, “Longterm outcome of cognition, affective state, and quality of life following subthalamic deep brain stimulation in Parkinson’s disease,” was published in the Journal of Neural Transmission.
Subthalamic nucleus-deep brain stimulation (STN-DBS) is a surgical treatment for Parkinson’s motor symptoms where a device that generates electrical impulses is implanted into specific regions of the patient’s brain.
Increasing evidence suggests that STN-DBS significantly improves motor symptoms as well as some non-motor symptoms, such as sensory issues and sleep disturbances. However, some reports point to a potential decline in cognition in Parkinson’s patients following STN-DBS.
Researchers here investigated the cognitive status of 104 Parkinson’s patients who received STN-DBS for nine years, from 1997 and 2006, at a single center in Germany.
Neuropsychological data from before the surgery were available for 79 of the patients, of whom 37, diagnosed with Parkinson’s for more than 11 years, were followed long term for a median of 6.3 years after surgery. During this time, they underwent several neuropsychological and motor tests.
In the remaining 42 patients, no follow-up was possible due to patients’ death (21 of the cases), loss of contact (nine patients) and patients’ refusal to undergo follow-up (12 patients).
Researchers measured patients’ dementia rate (using the Mattis dementia rating scale) and cognitive status, focusing on five domains — memory, executive function, language, attention, and working memory — mood (depression and anxiety), and quality of life using the Parkinson’s Disease Questionnaire and the 36-item Short-Form Health Survey.
Motor function was assessed using several motor tests, including the Unified Parkinson Disease Rating Scale motor subscore (UPDRSm) and Hoehn and Yahr Stage, a widely used clinical rating scale, with broad categories of motor function in Parkinson’s.
Prior to the surgery, 28 patients (75.7%) had mild cognitive impairment, while nine patients (24.3%) had normal cognitive function. Moreover, no patients showed signs of Parkinson’s-related dementia.
Patients in the two groups — with and without mild cognitive impairment — showed no differences in age, disease duration, response to treatment, and dosage with levopoda, motor function, and education. Mood and quality of life were also similar.
Patients’ verbal intelligence, measured by a multiple choice word test, and memory were lower in the mild cognitive impairment group.
After undergoing STN-DBS, 18.9%, or seven, of the patients had no cognitive impairment, while the remaining patients (41%) were diagnosed with either mild cognitive impairment (15 patients) or dementia (15 patients).
Mild cognitive impairment has been previously identified as a risk factor for dementia in Parkinson’s patients. Twenty-eight patients categorized as having mild cognitive impairment before STN-DBS developed dementia within 6.3 years after surgery.
Researchers observed a trend, although not statistically significant, between mild cognitive impairment before STN-DBS and progression to dementia according to the patients’ age, sex, and education at the beginning of the study.
Compared with non-demented Parkinson’s patients, those with dementia had longer disease duration (15 years versus 20.2 years, respectively) and more severe motor impairments (UPDRSm score of 23.7 versus 36.1), with demented patients showing a faster progression of several typical Parkinson’s symptoms — bradykinesia (slowness of movement), rigidity, impaired speech, posture, gait, and postural stability.
In general, researchers observed a decline in cognition, including memory and language, in all STN-DBS-treated patients in the 6.3 years after surgery. However, partial working memory (also referred to as short-term memory) was preserved and slightly improved in some cases.
Disease duration, but not age, at the time of DBS surgery had a significant relation to the risk of developing dementia.
“This observational, ‘real-life’ study provides long-term results of cognitive decline in STN-DBS-treated patients with presurgical [mild cognitive impairment] possibly predicting the conversion to dementia,” the researchers wrote.
“Although, the present data is lacking a control group of medically treated PD [Parkinson’s disease] patients, comparison with other studies on cognition and PD do not support a disease-modifying effect of STN-DBS on cognitive domains,” they concluded.