Sniffing Out Alzheimer's Disease

July 22, 2011 (Paris) -- Australian researchers say they’re a step closer to developing a simple smell test that may help predict which older adults will develop cognitive impairment and Alzheimer's disease.

The work is still very preliminary. But it appears that people who have memory loss and other signs of mental decline that can lead to Alzheimer's may have trouble discriminating between smells, says study leader Hamid R. Sohrabi, PhD, a neuropsychologist at Edith Cowan University in Perth, Australia.

William Thies, PhD, chief medical and scientific officer at the Alzheimer’s Association, tells WebMD that animal and lab research suggests there is an association between cognitive decline and smell, but that efforts to develop a commercial test have failed to date.

"It's not too surprising that the sense of smell changes, as the amyloid plaques and tangles that are thought to cause Alzheimer's develop in the same area of the brain that houses our olfactory pathway," he says.

The Sniffin' Stick Test

To determine whether cognitive impairment is associated with trouble smelling, Sohrabi and colleagues studied 308 people aged 46 to 86 with no memory problems.

All were given the "Sniffin' Stick" test, in which a person is presented three sticks, two of which have the same odor. Then he or she needs to pick out the one with the different odor. If the wrong stick is identified, the test is repeated with a slightly higher concentration of the odor, for a total of up to 16 times.

Over the next three years, 58 participants showed signs of cognitive decline, as determined by worsening scores on a simple questionnaire called CAMCOG that is used to assess memory and assist in the diagnosis of Alzheimer's.

Results showed that participants who had more trouble distinguishing between smells at the start of the study were more likely to shows signs of mental decline.

The analysis took into account other factors that can affect memory loss, such as age, sex, and education.

The findings were presented here at the Alzheimer's Association International Conference 2011.

Sohrabi says he hopes that test can be refined and someday be used to detect Alzheimer's disease early, before symptoms develop.

Other tests are further along in development, but none yet ready for clinical use.

"There is a long way to go,” Thies says. “You have to figure out which odor is best, test it in hundreds of people and validate it and then standardize the test so results are the same from one place to the next.”

Other tests are further along in development. These include tests that look for changes in the blood and cerebrospinal fluid that have been linked to the amount of Alzheimer's-associated plaque in the brain and an experimental test that looks for changes in the eye that can precede the development of Alzheimer's.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.