Importantly, it’s now becoming a standard neurological test to use the inability to smell particular odors as an indicator of which disease a person might have.
Alzheimer’s seems to have a list of about a dozen common smells that indicate the disease if the patient is unable to smell them. This helps distinguish Alzheimer’s from other forms of dementia and other medical problems that have mental side effects, like insufficient thyroid hormone, which is often misdiagnosed as Alzheimer’s.
Interesting, do you have a source at your fingertips?