But COVID-19 isn't the only reason you can lose your ability to smell. It can also signal the onset of Alzheimer's or Parkinson's disease.
So, being able to test this successfully would not only help track the recovery of COVID-19 patients, but also help physicians spot neurodegenerative conditions at an early stage.
Scientists from the United Kingdom say they’ve developed just such a test. What’s more, it will soon be available for at-home use.
The link between losing our ability to smell and neurodegenerative diseases was first observed in the 1970s. Since then, loss of smell has become recognized as an early symptom of Alzheimer's and Parkinson's, occurring many years before the first cognitive or motor symptoms appear.
Smell and neurological health are linked because nerve fibers connect olfactory (smell) receptors within the nasal cavity to higher olfactory centers at the base of the brain. And these areas are especially vulnerable to Alzheimer's and Parkinson's pathology.
This led scientists to look for ways to reliably test our ability to smell which can then be used as an early diagnostic tool.
Sniffin' Sticks Odor Identification Test
The Sniffin’ Sticks Odor Identification Test is one such test where a stick is scratched to release one of 16 different odors such as banana, cloves, garlic, and coffee.University of Pennsylvania researchers tested these odor-releasing sticks in 728 older adults who were either healthy, had mild cognitive impairment (MCI), or were diagnosed with Alzheimer's disease.
The neurologists were able to confirm that olfactory impairment is a regular feature of MCI and Alzheimer's and that carrying out a simple "sniff test" in addition to cognitive testing can enhance the accuracy of diagnosis.
Poor Smellers: Five Times More Likely to be Diagnosed
There’s another olfactory test, the Brief Smell Identification Test, that’s similar to Sniffin’ Sticks but contains only 12 odorants.Researchers at Michigan State University used this test to check the sense of smell of 2,462 healthy people with an average age of 75. Each participant was assessed as having either a poor, medium or good ability to identify the odorant. Researchers monitored each participant for more than ten years.
The results showed that people with a poor sense of smell were nearly five times more likely to develop Parkinson's disease than people with a good sense of smell.
"White Smells" Tests Offer More Effective Results
Stick tests, which were developed decades ago, are far from perfect. The amount of odor released depends on the extent to which the stick is scratched. This can affect the outcome of the test.These tests also rely on a patient's ability to detect and identify single odors. However, the ability to detect odors and to recognize them can vary greatly between people, even in those with a normal sense of smell. Some might recognize an odor but not be able to put a name to it; others may not recognize it at all, so there's a potential for misdiagnosis.
To eliminate these problems researchers at Rockefeller University, New York, developed a new test using "white smells."
Just as combinations of wavelengths and frequencies produce white light or white noise, white smells are generated from 30 different odors that can be tested at increasingly lower concentrations.
Neuroscientist Leslie Vosshall said, "We're really excited about these new tests. They focus on the problem of smell itself, because they don't force people to match smells to words."
Clinical trials back up her enthusiasm. They showed that the new test detected smell loss far more reliably than the conventional stick smell test options.
New at-Home Smell Test
In the United Kingdom, scientists at Queen Mary University, London, have just developed their own smell test. It's cheaper than existing stick tests, easier and faster to administer, and can be used at home by anyone experiencing a loss of smell.Even more exciting, this test is suitable for Parkinson's patients whose tremors make stick tests hard to use and unreliable.
The testing kit consists of capsules containing aromatic oils between two strips of tape. The capsules are easily crushed between the fingers and the tape strip is peeled to release the aroma.
A score is generated based on the ability to recognize the smells and the results can be sent to any doctor. Researchers have tested this capsule-based smell test in a small number of Parkinson's patients who found them easy to use.
Lead researcher Dr. Ahmed Ismail said, "Our capsule-based smell test can assist in the rapid diagnostic of various diseases linked to the loss of smell.
"These include chronic neurological conditions such as Parkinson’s and Alzheimer’s disease, as well as COVID-19...."
The at-home capsule-based smell test does not appear to be available in the United States yet.
- https://www.pennmedicine.org/news/news-releases/2016/december/sniff-test-may-be-useful-in-
diagnosing-early-alzheimers-disease - https://msutoday.msu.edu/news/2017/scratch-and-sniff-test-could-predict-parkinsons-even-earlier
- https://www.sciencedaily.com/releases/2017/10/171010200105.htm
- https://www.qmul.ac.uk/media/news/2021/se/researchers-develop-new-smell-test-for-parkinsons-
alzheimers-and-covid-19.html
