Alzheimer's disease is associated with memory loss and degeneration of the brain and cognitive functions but those symptoms don't usually happen until the disease has already progressed to its advanced stages. There is also the fact that not all patients are eager to undergo invasive and expensive tests for the disease, which is why many patients are not correctly diagnosed until it is already too late.

A team of researchers from McGill University, however, has found a potentially effective way to diagnose patients for early symptoms of Alzheimer's disease by way of inexpensive scratch-and-sniff tests.

According to experts, one of the noticeable changes in Alzheimer's patients is their loss of sense of smell or inability to identify odors, so the team of researchers tested the link between a person's declining sense of smell and their risk of developing AD.

"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," first author Marie-Elyse Lafaille-Magnan said.

Scratch-And-Sniff For Diagnosis

In order to test the link, the team recruited adults who are at risk for Alzheimer's and tested their sense of smell against the quantity of AD-related proteins through lumbar punctures.

A total of 274 adults averaging 63 years of age agreed to participate in the odor identification tests, with 100 of the subjects also agreeing to regular lumbar punctures to determine the amount of AD-related proteins in their cerebrospinal fluids. All participants have at least one parent who had been diagnosed with Alzheimer's disease and were at risk for AD themselves.

The participants were given multiple choice scratch-and-sniff tests using a varied set of odors — from gasoline to bubble gum. Those who volunteered for lumbar punctures were also tested on their ability to identify odors, and their results for both tests were compared.

What they found was that biological markers for Alzheimer's were most evident in adults who have the most difficulty in the odor identification tests.

"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," Lafaille-Magnan said.

Odor Identification As Replacement For Invasive Tests

The researchers are confident that their strategy of administering odor identification tests on potential AD patients could help medical practitioners with the early detection and treatment of the disease. However, the team also emphasizes that a scratch-and-sniff test is in no way a replacement for the current expensive and invasive tests.

They clarify that checking for the biological markers of AD-related proteins is still the better approach for now, but that the odor identification test could also be used along with it to check how fast the disease is progressing.

"This means that a simple smell test may potentially be able to give us information about the progression of the disease ... However, problems identifying smells may be indicative of other medical conditions apart from AD and so should not be substituted for the current tests," co-author Judes Poirier warns.

Poirier is the Douglas Institute director of research program on aging, cognition and Alzheimer's disease.

The study titled "Odor identification as a biomarker of preclinical AD in older adults at risk" has been published in the journal Neurology.