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Why A Peanut Butter Test For Alzheimer's Might Be Too Simple

Alzheimer's disease can be tough to diagnose, especially early on. Doctors can order brain scans and assay spinal fluids. But existing tests are imperfect and some can be invasive.

So you might understand the appeal of an alternative that researchers at the University of Florida in Gainesville tried. They had asked patients to sniff a dab of peanut butter during a routine test of cranial nerve function. Later, the team wondered if it could help them figure of it someone might be in the early stages of Alzheimer's.

In the test, a patient sniffs a little peanut butter one nostril at a time. The clinicians then measure the distance at which patients can detect the smell.

After administering the test about 100 times, Jennifer Stamps, a graduate student at the University of Florida's McKnight Brain Institute Center, says that she and her supervisor, neurologist Kenneth Heilman, noticed that patients in the early stages of Alzheimer's disease weren't able to smell as well from their left nostril.

"When we analyzed the data we were blown away," Stamps tells Shots. Impairment of the left nostril corresponded with a positive Alzheimer's diagnosis every time. It made sense to the Florida team, because with Alzheimer's, the left part of the brain is usually affected first. Smell, unlike sight, is ipsilateral: The side of the body sensing the stimulus and the side of the brain processing the information are the same.

They published the results of a preliminary study in the Journal of Neurological Sciences. Heilman's clinic has now started using the test to verify Alzheimer's diagnoses. The team is also looking to do a big, long-term study to confirm their findings to explore see if the sniff test could be used to actually diagnose Alzheimer's.

There's some promise there, but also a lot of doubt.

"The idea that smell is altered in Alzheimer's disease dementia patients is well known, and this is nothing new," neurologist David Knopman from the Mayo Clinic tells Shots.

Knopman says this study is nothing more than an interesting observation. The study itself acknowledges that the findings aren't fully verified. And the study sample of 94 patients (only 18 of whom were diagnosed with Alzheimer's) is too small to be conclusive.

Even if the researchers do a bigger study, Knopman is skeptical that the findings will prove useful. People can lose their ability to smell as they get older for many reasons, he says.

And there's another disease, dementia with Lewy bodies, that shares characteristics with both Alzheimer's and Parkinson's disease. Smell impairment is even more severe in DLS patients, Knopman says.

"It would get you into that ballpark of Alzheimer's versus Lewy body disease, but it wouldn't help you distinguish between those two," he says.

Stamps remains cautiously optimistic about the prospects for the test. "It's helped us tremendously," Stamps says. "Because if you see someone that doesn't have that asymmetry, that you think might have Alzheimer's, it's going to lead you to look more closely for other things."

But for now, Stamps warns: Don't try this at home. Having slight differences between your left and right nostrils is normal, and you might end up freaking out over nothing.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

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