If you are starting to see symptoms of Alzheimer’s disease (AD) in someone, the damage is already serious. It is thought that as many as twenty years might elapse from the start of the AD until diagnosis. There is, of course, a lot of interest in finding a way to detect the disease earlier. Scientists have been trying to use smell tests to detect both dementia, Parkinson’s and AD for several years, although they are imperfect; a new study published in Neurology has assessed an odor identification test together with biological testing for diagnosing AD.
Researchers know that for now, early diagnosis is the best tool we have to fight AD. “Despite all the research in the area, no effective treatment has yet been found for AD,” said study author Dr. John Breitner, the Director of the Centre for Studies on Prevention of Alzheimer's Disease at the Douglas Mental Health University Institute. “But, 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%.”
There is a clear familial risk associated with Alzheimer’s. This study had 300 participants with an average age of 63 and who had a parent that had suffered from AD. They took multiple-choice tests in which they had to scratch, sniff, and identify different scents like gasoline or bubble gum. One hundred of these individuals also regularly donated cerebrospinal fluid through lumbar punctures; the researchers were thus able to measure the levels of proteins that are associated with AD. Connecting the CSF samples with the smell tests, it was found that those who had the most trouble correctly identifying odors also had biological indications of AD.
“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,” explained the first author of the report, Marie-Elyse Lafaille-Magnan, a doctoral student at McGill. “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 means that a simple smell test may potentially be able to give us information about the progression of the disease that is similar to the much more invasive and expensive tests of the cerebrospinal fluid that are currently being used,” said study author, Judes Poirier, the Director of the Research Program on Aging, Cognition and Alzheimer’s Disease, Douglas Mental Health University Institute. “However, problems identifying smells may be indicative of other medical conditions apart from AD and so should not be substituted for the current tests.”
The researchers have noted that there is much work that remains in order to understand how differences in olfaction are related to AD progression. Other researchers believe that declines in a person’s ability to smell are related to poor health. A 2016 study linked olfactory dysfunction and increased risk of death; again the underlying biological mechanisms are unknown.