Can changes in your sense of smell signal Alzheimer's disease?

The olfactory nerves tell your brain what kind of molecules have been arriving in your nose.  Your brain then must process that information so that your mind can understand it, understanding the information as various odors.  So can Alzheimer's disease affect the parts of your brain that process information from your nose and interprets it as smells?  Can this be used to diagnose Alzheimer's disease?  Maybe so.

Alzheimer's and Dementia; the Journal of the Alzheimer's Association recently published an article discussing this -- but in kind of a roundabout manner.  The article was "Intact global cognitive and olfactory ability predicts lack of transition to dementia."  So, if your sense of smell is okay, the probability that you are developing Alzheimer's disease is low.

I didn't pay to download the article, so I only had access to the summary information.  But here are my takeaways.

The article documents the results of a study of 1,037 older, urban living adults.  They used the 40-item University of Pennsylvania Smell Identification Test to assess the subjects' sense of smell, following up with 749 participants after four years.

Their conclusion was,  "Olfactory and cognitive impairment each predict dementia."  And "Odor identification testing adds value to global cognitive testing, and together can identify individuals who rarely transition to dementia, thereby avoiding unnecessary diagnostic investigation."

It seems like a no-brainer that, taken together, a deteriorating sense of smell and deteriorating cognitive function would predict oncoming dementia.  Heck, deteriorating cognitive function itself predicts oncoming dementia, doesn't it?

Recall that for a diagnosis of Alzheimer's disease you need two things: deteriorating cognition as demonstrated through testing and biomarker evidence.  In my case, biomarker evidence was from expensive MRIs showing atrophy of my brain.  They don't say it in so many words, but it appears that the researchers are proposing that a smell test might be used as a biomarker to diagnose Alzheimer's disease.  Or, more likely, an un-biomarker that can rule out Alzheimer's disease when sense of smell has not deteriorated.   This would avoid the cost of MRIs as well as even more expensive PET scans.  (We continue to look for a blood test -- maybe soon -- that would likely be cheaper than imaging.)