Researchers Breathing Easier as Smell Tests May Diagnose Parkinson’s Earlier

Two new tests that diagnose smell dysfunction are an effective method to detect Alzheimer’s and Parkinson’s diseases across different patient populations, a study shows.

The study, “SMELL-S and SMELL-R: Olfactory tests not influenced by odor-specific insensitivity or prior olfactory experience,” was published in the journal PNAS.

Smell dysfunction is a common medical disorder that tends to be under-diagnosed, but can lead to serious consequences. It also has been found to be an early biomarker of diseases associated with neurodegeneration such as Alzheimer’s and Parkinson’s. In fact, smell dysfunction in these disorders appears before the onset of cognitive issues.

Currently, the clinical tests that are in place to assess a patient’s sense of smell come across two main challenges. First, individuals can have wildly varying sensitivities to different smells, making the test unreliable because some patients react smell less, or more, than an average person. Secondly, when an individual has been exposed to a smell prior, the familiarity can bias the test.

So, researchers set out to develop a test that would be useful in diagnosing these diseases. They developed two new tests that eradicate these biases through the help of “white smells.” The idea behind “white smells” is similar to the idea of white light or white noise, which is a combination of different wavelengths of light or frequencies of sound that together produce white light or white noise, respectively.

Researchers compounded 30 different odor molecules to create “white smells.” These tests, called SMELL-S and SMELL-R, require patients to distinguish between white smells with overlapping ingredients (SMELL-R) and white smells at increasingly higher dilutions (SMELL-S).

“We’re really excited about these new tests,” neuroscientist Leslie Vosshall, PhD, a Howard Hughes Medical Institute investigator, said in a press release. “They focus on the problem of smell itself, because they don’t force people to match smells to words.”

Researchers have conducted clinical trials to evaluate the use of these tests at the The Rockefeller University Hospital in New York and the Taichung Veterans General Hospital in Taiwan.

Results of this clinical trial showed that SMELL-S and SMELL-R were able to detect smell loss more accurately than other conventional options. Furthermore, this study showed there was less bias in scores between the North American and the Taiwanese patients, indicating it could be adopted worldwide for the detection of Alzheimer’s and Parkinson’s diseases.

“Developing a universal olfactory test to reliably diagnose smell dysfunction is of great clinical importance not only because of the negative effects of smell dysfunction on quality of life but because olfactory dysfunction is frequent, can be clinically managed, and may be an effective biomarker for predicting Alzheimer’s disease, Parkinson’s disease, and other neurodegenerative diseases,” the researchers wrote.

“The goal is to use changes in the sense of smell, along with other biomarkers, to identify underlying causes of these neurological disorders very early, and so potentially improve treatment,” said Julien Hsieh, MD, a Rockefeller clinical scholar and lead author of the paper.