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Hypertension in Cognitively Healthy Older Adults Is Associated With Gray Matter Volume Loss


 

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CHICAGO—Cognitively healthy older adults with hypertension have gray matter volume loss much like that seen in patients with Alzheimer’s disease, according to data presented at the 94th Scientific Assembly and Annual Meeting of the Radiological Society of North America. “This gray matter volume loss persists despite adjusting for multiple confounders, such as age, education, head size, infarcts on MRI, and future conversion to mild cognitive impairment and Alzheimer’s disease,” reported Cyrus Raji, an MD/PhD candidate at the University of Pittsburgh School of Medicine, and colleagues. “We also found an interaction between hypertension and conversion to mild cognitive impairment during the five-year course of the study. We tested a similar interaction with Alzhei­mer’s conversion after five years but did not find a relationship.”

In the Cardiovascular Health Study Cognition Study (CHS-CS), Mr. Raji and colleagues used voxel-based morphometry to analyze gray matter volume in 147 cognitively healthy adults older than 70, of whom 50 had hypertension (defined as blood pressure higher than 140/90 mm Hg or use of antihypertension medication). Participants in the CHS-CS are drawn from a general community cohort, minimizing the referral bias of specialty clinics. The 1.5 T–spoiled gradient echo scans for each subject were acquired using three-dimensional volumetric MRI, warped into a stereotactic space, and segmented into gray matter, white matter, and CSF. Each scan was then modulated to convert the tissue density measurements into volume measurements and smoothed into a parametric statistical framework. Multivariate modeling was used to account for potential confounders. Mr. Raji noted that the study would have been more difficult to perform without the voxel-based morphometry method, which permitted quick, thorough evaluation and comparison of brain volumes. “With this technology, we look at the entire brain,” he said. “We’re not biased by region-of-interest ­approaches.”

Hypertension Is Linked to Lower Gray Matter Volume
The investigators found that hypertension was significantly associated with lower gray matter volumes in the hippocampus, posterior cingulate, and precuneus. Subjects with hypertension who converted to mild cognitive impairment within five years after their scan had even lower gray matter volumes than mild cognitive impairment converters with hypertension. “Collectively, these results suggest that cognitively normal persons with hypertension have gray matter volume loss in brain regions known to be affected by Alzheimer’s [disease],” Mr. Raji told Neurology Reviews. “This work should motivate additional study into the link between hypertension and Alzhei­mer’s [disease] and provide impetus for better hypertension prevention and treatment in the elderly.”

Good Vascular Health Equals Good Brain Health
The CHS-CS results suggest that future studies of brain atrophy in Alzheimer’s disease and aging should control for effects of hypertension and other types of vascular disease. “In attempting to identify patterns of brain atrophy specific to neurodegeneration, vascular disease—such as hypertension, type 2 diabetes, ischemic heart disease, stroke, lacunar infarcts, and small vessel ischemic disease—could be a substantial confounder, because we find this Alzheimer’s disease–like atrophy in a cognitively normal cohort with hypertension,” said Mr. Raji.

Perhaps of more clinical relevance is the possibility that gray matter atrophy in persons who have vascular disease may be linked to a higher risk for cognitive impairment and dementia. “Good vascular health is linked to good brain health,” Mr. Raji commented. “Vascular conditions like hypertension are prevalent in the elderly and are treatable and preventable, so identifying whether they are risk factors for Alzheimer’s disease is of tremendous public health importance. We are currently investigating whether obesity, a powerful risk factor for hypertension and other vascular diseases, is itself a predictor of gray matter volume loss in the elderly.”


—Rose Fox

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