UC HEALTH LINE: Researchers Team Up for Study on Smell Loss, Neurodegenerative Disease

CINCINNATI—Most of the patients with smell loss who visit UC Health otolaryngologist Allen Seiden, MD, can pinpoint the exact time they lost their sense of smell: it was after a bad cold, a head injury or an exposure to a chemical or other substance. But for other patients, their loss of a basic sense is completely unexplained.

Those patients, diagnosed with "idiopathic olfactory loss,” have few treatment options. To try to understand more about their case and the possible causes of their condition, Seiden is partnering with UC psychology researcher Bob Frank, PhD.

They are conducting a study to find patients with idiopathic smell loss—both new and past patients—and learn how their loss of smell has progressed. More importantly, Seiden and Frank want to know another aspect of the patient’s health: Have they developed a neurodegenerative disease since their loss of smell?

"It’s become apparent that one of the early manifestations of neurodegenerative disease, like Alzheimer’s, Parkinson’s or Lou Gehrig’s disease, is possibly olfactory loss,” says Seiden. "For example, Alzheimer’s disease forms neurofibrillary tangles on the nerve fibers of the brain—they tend to form earliest on the olfactory nerves.

"If we are able to follow these patients over time, and they go on to develop some clear pathology or cognitive problems, that may suggest a link between olfactory loss and these diseases. If so, we can learn what the incidence rate is.”

Frank, associate dean for research and graduate study at UC’s McMicken College of Arts and Sciences, has studied taste and smell—in particular, how to clinically evaluate the loss of smell. He says typical smell tests can be problematic for patients with early neurodegenerative disease.

"Naming a smell requires a lot of cognitive efforts,” says Frank. "Patients need to remember previous smells and their name, as well as decide which odor is present. If a patient is in the early stages of Alzheimer’s disease or dementia and they don’t do well on a smell test, they may just not do well on any test.”

To better measure patients’ sense of smell, Frank developed a sniff magnitude test, which measures the length of a sniff without requiring patients to name the scent presented.

He says that when encountering an odor, people typically take a shorter, quickened sniff. The sniff magnitude test allows clinicians to measure patient’s sniff when presented with an odor: If they are not taking shorter sniffs, it’s likely because they can’t smell anything at all.

The sniff magnitude test is just one of the tests patients in Seiden and Frank’s study will participate in—they also will perform basic memory and cognition tests to measure brain function.

Frank says a better understanding of the link between the loss of smell and neurodegenerative disease could lead more patients with idiopathic olfactory loss to further evaluation or specialized treatment early in their disease. But first, researchers need to be able to learn more about these patients. 

"We’re trying to categorize the relationships that we see emerging,” says Frank. "Is olfactory loss mostly associated with the development of Alzhiemer’s and related diseases, or just occasionally? We’re in the process of trying to better understand the relationship between the sense of smell and the diseases of aging and the aging brain. This study will allow us to begin that process.