As the world’s population ages, an ever-growing number of people are experiencing Alzheimer’s disease and other forms of dementia. The World Health Organization reports that more than 35 million people live with dementia today. That number is expected to grow to more than 65 million by 2030 and 115 million by 2050.
Dementia is a progressive disease, starting with occasional forgetfulness and eventually developing into a major disability. Although there are some medications on the market to treat dementia, and there are others in development, they can’t reverse damage that’s already been done — they can only help keep the brain from deteriorating further. This makes it vitally important to spot the warning signs of dementia as early as possible.
New research published today in Radiology explains a technique that can be used to detect dementia long before patients show any signs of mental decline.
Taking a Look Under the Hood
In the study, researchers recruited 148 healthy volunteers and 65 people who already showed signs of mild cognitive impairment. Their average age was 76. Researchers performed 25 neurocognitive tests on the volunteers to build a detailed profile of their abilities. Then, they ran a brain scan on each person using a type of magnetic resonance imaging (MRI).
The specific technique, called arterial spin labeling MRI (ASL MRI), measures the penetration of oxygen- and nutrient-rich blood into the tissues, using blood as a naturally-occurring contrast agent. This lets doctors examine the metabolic rates of different regions of the brain, a task currently performed using positron emission tomography (PET) scans.
Eighteen months later, the researchers called the participants back to the lab for another round of cognitive testing to see what had changed. About half of the initially healthy people in the sample showed signs of cognitive decline, while the other half remained stable.
The researchers then examined the brain scans from the start of the study to see if there were any differences between the participants who stayed stable and those who went on to show signs of dementia. They found significant differences in the blood penetration levels in one specific part of the brain: the posterior cingulate cortex (PCC).
The PCC is part of the default mode network (DMN), the network of brain regions responsible for inward-facing tasks like self-reflection.
“The DMN is more active during rest, and it is believed that it is necessary to restore brain function,” said study author Dr. Sven Haller, a neuroradiologist at the University of Geneva in Switzerland, in an interview with Healthline. “Simply speaking, the DMN re-synchronizes the brain so that the brain is again fresh and responsive. In dementia, the DMN activation decreases, which might be one of the reasons that the brain ‘recovers’ less and consequently is less [high] performing.”
People who went on to show signs of cognitive decline at the 18-month mark showed reduced blood flow to their PCC at the beginning of the study. In fact, their PCC blood flow patterns more closely resembled those of the group who showed cognitive impairment at the start of the study.
Most neuropsychological tests can’t detect dementia at its earliest stages. That’s because people with mild dementia are able to perform functional compensation. In other words, they have extra mental resources at their disposal to make up for forgetfulness. These resources pick up the slack left by other systems that might be damaged by early dementia so that the person is still able to function normally. However, this compensation doesn’t last forever.
A New Method for Early Detection
Haller hopes that his discovery will help make early detection of dementia easier and cheaper. “In our study, ASL performed as [well] as cognitive testing,” said Haller. “Yet ASL only takes [an] additional five minutes for an already routinely performed MRI, while the cognitive testing is very challenging for the patient and takes a few hours.” PET scans are also time-consuming and expensive, and they require injecting patients with a radioactive contrast agent that can trigger a rare allergic reaction in some people.
Ideally, Haller hopes, the techniques could be combined. ASL MRI and neurocognitive testing together provide a more accurate diagnosis than either method alone. From there, a specialized PET scan could examine the accumulation of specific amyloid proteins related to dementia to confirm the diagnosis. This would spare patients the current diagnostic process, which requires two PET scans: one metabolic scan, which ASL would replace, and the second amyloid scan.
For dementia, early diagnosis is key. “A potential medication will probably not be able to restore lost cognitive function in advanced dementia, yet [will] hopefully stop or at least slow down the neurodegenerative process,” Haller said. “Consequently, the earlier the detection, the earlier the treatment and the better the effect. ASL might be a simple, non-invasive, fast, and operator-independent tool which might contribute to the early detection of cognitive decline.”