Is type 2 diabetes linked to lower blood flow in parts of older adults’ brains?

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Type 2 diabetes increases the risk of dementia, including Alzheimer’s disease. Previous studies of brain changes underlying cognitive impairment in type 2 diabetes have often used conventional structural MRI to detect large-scale changes associated with cerebrovascular disease, such as white matter hyperintensities or infarcts. The authors note that these changes likely reflect end-stage manifestations of a chronic decrease in cerebral blood flow. MRI techniques that measure blood flow may help clarify mechanisms preceding irreversible brain tissue damage and provide a marker of cognitive decline risk. Arterial spin labeling (ASL) MRI may be useful for detecting blood-flow deficits in type 2 diabetes and related conditions.

The researchers examined associations among type 2 diabetes, cerebral blood flow and cognition in 49 well-characterized older adults without dementia. Using a 3T GE scanner, they obtained a standard T1-weighted scan and a pseudocontinuous ASL sequence optimized for older adults by increasing the post-labeling delay, allowing blood more time to reach brain tissue; they measured regional blood flow in regions of interest derived using FreeSurfer. Participants also completed a neuropsychological assessment.

There were no significant differences in cortical thickness or regional brain volume between participants with and without type 2 diabetes. After adjustment for age, sex, coexisting vascular risk factors and reference blood flow in the postcentral gyrus, those with diabetes had lower blood flow in the hippocampus and the inferior temporal, inferior parietal and frontal cortices. Lower blood flow was associated with poorer memory and executive function/processing speed. The significant associations between lower regional blood flow and poorer executive function/processing speed remained after adjustment for diabetes.

The authors conclude that cerebral blood flow is reduced in older adults with type 2 diabetes and suggest that blood-flow changes likely precede changes in brain volume. Compared with nondiabetic controls, participants with diabetes had lower blood flow in regions prone to Alzheimer’s pathology, including the medial temporal lobe and inferior parietal regions. The findings add to research suggesting that perfusion deficits may underlie cognitive decrements frequently seen in older adults with type 2 diabetes. They also suggest that blood flow measured by ASL MRI may be an early, important marker of cognitive impairment risk in type 2 diabetes and related conditions.