Researchers have identified an indicator of Alzheimer's disease, which could help earlier diagnosis and lead to noninvasive ways of tracking progression of the disease in patients.
Current diagnostic tests performed by physicians are largely based on memory. This is problematic because by the time you start showing signs of memory loss, you could have had the disease for up to 20 years.
Now, scientists at McGill University in Quebec, looking for a way to spot Alzheimer's earlier on have shown for the first time that loss of smell could be an early indication of the disease.
In a study published in Neurology, researchers studied 300 people at risk of Alzheimer's disease because they had a parent who suffered from it. They were given multiple-choice scratch and sniff tests, asking them to identify smells ranging from bubble gum to gasoline.
One hundred of the volunteers, with an average age of 63, also allowed themselves to be regularly tested via lumbar puncture for proteins related to Alzheimer's disease in their spinal fluid.
The researchers found that those who had the most difficulty identifying smells in the scratch and sniff tests had the most biological indications of Alzheimer's disease.
“This is the first time that anyone has been able to show clearly that the loss of the ability to identify smells is correlated with biological markers indicating the advance of the disease,” said Marie-Elyse Lafaille-Magnan, first author of the study, in a statement.
“For more than 30 years, scientists have been exploring the connection between memory loss and the difficulty that patients may have in identifying different odors. This makes sense because it’s known that the olfactory bulb (involved with the sense of smell) and the entorhinal cortex (involved with memory and naming of odors) are among the first brain structures first to be affected by the disease.”
This smell test could be used to track the disease before other symptoms even appear, the researchers said, and even reduce symptoms once they begin.
"If we can delay the onset of symptoms by just five years, we should be able to reduce the prevalence and severity of these symptoms by more than 50 percent," Dr. John Breitner, the director of the Centre for Studies on Prevention of Alzheimer's Disease at McGill University, said.
The researchers say that more needs to be done to see if the sense of smell of people with Alzheimer's diminishes as the disease progresses. However, they are hopeful with further study, a test could be used instead of the more invasive, and costly, procedures such as lumbar punctures.
For now, though, the director of research warned against using smell alone to diagnose the disease.
“Problems identifying smells may be indicative of other medical conditions apart from Alzheimer's disease and so should not be substituted for the current tests.”