MIAMI BEACH – Changes in brain volume and networks could someday predict which patients with Parkinson's disease are at highest risk to develop dementia, according to recent studies.
It has been known for some time that hippocampal atrophy, for example, is a common feature of Parkinson's disease with dementia. However, a recent study is the first to show that the decrease in hippocampal volume could predict which patients are at a higher risk for development of dementia, Irena Rektorové, Ph.D., said at the World Federation of Neurology World Congress on Parkinson's Disease and Related Disorders.
“What is important from a practical point of view is that atrophy of hippocampus probably predicts a switch to dementia,” said Dr. Rektorové, who is on the neurology faculty at Masaryk University in Brno, Czech Republic.
A Swiss research team calculated that the risk for dementia increases almost 25% with every 0.1 mL decrease in hippocampal volume, based on a study of 70 patients who had subthalamic deep brain stimulation (Parkinsonism Relat. Disord. 2009;15:521–4). The 14 patients in this cohort who later developed dementia had significantly smaller preoperative hippocampal volumes than did those who did not develop dementia.
Dr. Rektorové provided some additional perspective on the extent of volume changes. “Hippocampal atrophy is definitely present in those with Parkinson's disease, and especially those with Parkinson's disease dementia, but it is lower than atrophy with Alzheimer's disease.”
Using voxel-based morphometry, other researchers have reported gray matter loss in the frontal areas of the brain in patients with Parkinson's disease that extends to the temporal, occipital, and subcortical areas with comorbid dementia (Brain 2004;127:791–800). Occipital atrophy, in particular, may be an important distinction between Parkinson's patients with and without dementia.
Mild cognitive impairment (MCI) is common among people affected by Parkinson's disease. A goal for researchers is to identify “the malignant form” of MCI that will progress to dementia, said Dr. Rektorové, who had no relevant disclosures.
“Would brain imaging of mild cognitive impairment or dementia in Parkinson's disease be of any help?” Dr. Rektorové asked. It is possible, she said, based on the promising results of multiple studies using
“These studies show posterior rather than anterior cortical involvement in Parkinson's disease dementia versus Parkinson's disease alone,” Dr. Rektorové said.
A study using
In a study currently in preparation, Dr. Rektorové and her colleagues found decreased activity in certain brain areas of patients with Parkinson's disease, compared with controls, while performing the Stroop test. During this measure of executive function, decreases were seen in the cuneus, middle temporal gyrus, inferior parietal lobule, insula, and medial dorsal nucleus of thalamus.
“It is worth mentioning that these Parkinson's disease patients were medicated and they had no cognitive impairment in this task,” Dr. Rektorové said. “They actually performed as well as healthy controls.”
It also could be that what is not turned off during executive functioning in Parkinson's disease plays a role in cognitive impairment, Dr. Rektorové said. During executive task performance in healthy volunteers, fMRI shows deactivation of the medial prefrontal cortex, posterior cingulate cortex, precuneus, and medial temporal cortices.
However, this imaging also shows that people with Parkinson's disease may fail to shut off this resting brain activity, called the “default mode network.” Dr. Rektorové said the full function of the default mode network is not yet known.
For the first time, other researchers have used fMRI to assess the potential contribution of the default mode network in patients with Parkinson's disease (Arch. Neurol. 2009;66:877–83). They demonstrated a decrease in ventral medial prefrontal cortex activity similar to controls during executive functioning. But participants with Parkinson's disease featured increased precuneus and posterior cingulate cortex activity, whereas controls showed deactivation in these regions.