A simple test of a person's ability to detect odours and non-invasive eye exams might someday help doctors learn whether their patients are at risk of Alzheimer's disease.
With Alzheimer's disease spreading fast among the world's aging population, researchers are increasingly focused on the search for new ways to detect and treat the brain-killing disease in its earliest stages.
In two separate studies on the connection between dementia and sense of smell, teams of researchers found a decreased ability to detect odours in older people, as determined by a common scratch-and-sniff test, could point to brain cell loss and the onset of dementia.
In two other studies, researchers showed non-invasive eye exams also might offer a way to identify Alzheimer's in its early stages.
The findings -- which were presented Sunday at the Alzheimer's Association International Conference in Copenhagen, Denmark -- raise hopes doctors could develop simple, inexpensive diagnostic tools that would hunt down reliable biomarkers of a disease.
Alzheimer's is a progressive and incurable disease that begins in areas of the brain associated with memory. It is the leading cause of dementia in older people, usually striking after the age of 65. It robs people of their cognitive abilities, speech and, ultimately, their identities. Eventually, it shuts down the most basic body functions, resulting in death.
Scientists have long suspected a link between a person's ability to detect odours and the slow destruction of brain cells caused by Alzheimer's disease, particularly in the disease's early stages.
In one trial, researchers led by Reisa Sperling in the Harvard Aging Brain Study focused on 215 clinically normal people who had no complaint of memory loss and were living in their communities. They were given the University of Pennsylvania Smell Identification Test, a packet of scratch-and-sniff panels with 40 different odours.
The participants then underwent more exhaustive mental and physical evaluation, including annual cognitive evaluations; genetic analysis of known risk factors; and brain scans using MRI's and positron emission tomography.
The PET scans used an injected substance to determine the level of beta-amyloid protein deposits inside each participant's brain. Clumps of beta-amyloid fragments, which are a distinguishing characteristic of Alzheimer's, form plaques between brain cells and are thought to kill them.
The MRI scans measured each subject's entorhinal cortex, which is located in the brain's medial temporal lobe near the hippocampus and plays a role in processing smell and forming short-term memories. It is also one of the first regions of the brain affected by Alzheimer's.
What the researchers found was people who performed poorly on the odour-identification and memory tests also showed elevated levels of beta amyloid proteins in their brains, as shown in PET scans and other tests. Their entorhinal cortexes were also thinner, which is associated with poorer memory.
"It's an intriguing finding," said Matthew Growdon, a fifth-year student in a joint program between Harvard Medical School and the Harvard School of Public Health.
-- Washington Post