December 22nd

Measuring thickness of brain may help determine risk of Alzheimer’s disease

There is no cure for Alzheimer’s disease, and as far as treatment goes, the best doctors can do (for now) is try to slow its progression. Identifying people in the earliest stages of the disease — even before any symptoms appear — would thus be very useful.

Using MRI scans to measure the thickness of specific parts of the brain can help accomplish this. A new study from the journal Neurology reports that an “AD signature” can predict which people with normal brain function are most likely to suffer cognitive decline in the relatively near future.

Researchers turned to the Alzheimer’s Disease Neuroimaging Initiative database, a research effort designed to test whether biomarkers and test results can be used to measure the progression of early Alzheimer’s disease. They identified 159 people (average age 75.5 years) who were cognitively normal and had good-quality MRI scans. The scans measured the thickness of the cortex (the brain’s so-called gray matter) in nine places and averaged those values to come up with a single score. This was the AD signature, or ADsig for short, and the researchers used it to divide subjects into three categories: those at high risk for developing Alzheimer’s, those with average risk; and those at low risk.

Three years later, 125 of those subjects took tests to evaluate their brain function. And indeed, the people considered at greatest risk of developing Alzheimer’s were more than three times as likely to show signs of cognitive impairment compared with those classified as being at average risk for the disease. More specifically, three out of the 14 subjects (or 21 percent) with ADsig scores suggestive of high risk showed signs of cognitive decline, compared with six out of the 90 subjects (or 7 percent) whose ADsig scores indicated normal risk. None of the 21 people with low-risk ADsig scores experienced cognitive decline over the three-year period.

The ADsig measurement was very precise. On average, the cortex was only 1.5 millimeters thinner in people in the high-risk category than it was in people in the average-risk category.

In the study, the researchers caution that their biomarker needs to be tested in more people who are followed for a longer period of time. But they also expressed optimism that they were on the right track.

As it happens, 84 of the study volunteers also had given samples of their cerebrospinal fluid. Among them, 60 percent of those deemed high risk according to ADsig had levels of amyloid beta plaque consistent with Alzheimer’s. In contrast, just 36 percent of those in the average-risk group and 19 percent of those in the high-risk group had plaque levels suggestive of Alzheimer’s disease.

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