Various tests for diagnosing Alzheimer's disease have become available in recent years, although they remain imperfect diagnostic tools. Now researchers at Duke University report that using a combination of tests – two types of brain scans along with analysis of spinal fluid -- improves the ability of doctors to diagnose mild cognitive impairment (MCI), a serious form of memory loss that often precedes Alzheimer's.
These tests are still undergoing study, although they are increasingly being offered at various medical centers. And it's unlikely that most people with serious memory problems would undergo all three costly tests. But the findings highlight the difficulty involved in determining who will go on to develop Alzheimer's disease.
Currently, Alzheimer's can be diagnosed definitively only after death, when an autopsy reveals the telltale plaques and tangles that litter the brains of those affected by the disease. But scientists are getting closer to developing tests that can diagnose Alzheimer's in its earlier stages, before damage to the brain becomes extensive. Doctors hope that early diagnosis will offer the possibility of early, and more effective, treatment that may slow, or even stop, the progression of the disease.
For the study, which appeared in the journal Radiology, the researchers studied two different types of brain scans -- magnetic resonance imaging (MRI) and positron emission tomography (PET) -- as well as analysis of cerebrospinal fluid, the fluid that bathes the brain and spinal cord.
Participants also received routine medical exams, including testing of memory and thinking skills. The researchers found that getting both types of scans as well as a spinal fluid analysis proved more effective than any test alone in diagnosing mild cognitive impairment.
"This study marks the first time these diagnostic tests have been used together to help predict the progression of Alzheimer's," said study author Dr. Jeffrey Petrella of Duke University. "Each of these tests adds new information by looking at Alzheimer's from a different angle." Although brain scans using MRI and PET are often used together to diagnose probable Alzheimer’s, the use of these scans together with analysis of cerebrospinal fluid for specific biomarkers is not yet part of routine medical practice.
The Duke team collected data from 97 older adults with mild cognitive impairment who were part of the Alzheimer's Disease Neuroimaging Initiative, a national study that collects data in hundreds of elderly patients with varying levels of memory and cognitive problems. All the participants got regular memory tests, as well as MRI and PET brain scans and spinal fluid tests, for up to four years. The combination of all three tests was able to reduce the current uncertainty of who potentially was at high risk of developing Alzheimer's within the next few years from over 40 percent to under 30 percent. In other words, the tests aimed at identifying MCI patients who were most likely to go on to develop Alzheimer’s.
The uncertainty highlights the difficulty involved in diagnosing early Alzheimer's. The researchers noted that while the tests clearly provided the most diagnostic information in combination, additional studies are needed to better understand their role in a clinical setting. "Additional studies, including those looking at the cost effectiveness of these tests, are also needed," they said.
"Given that the definitive gold standard for diagnosing Alzheimer's is autopsy, we need a better way to look into the brain," added P. Murali Doraiswamy of Duke, another study author. "In people with mild memory complaints, our accuracy is barely better than chance."
Source: Duke University Medical Center. Shaffer JL, Petrella JR, Sheldon FC, et al: "Predicting Cognitive Decline in Subjects at Risk for Alzheimer' Disease by Using Combined Cerebrospinal Fluid, MR Imaging and PET biomarkers." Radiology, Dec. 11, 2012