Evidence from the Penn Smell and Taste Center suggests that the University of Pennsylvania Smell Identification Test, or UPSIT, is having a new, but familiar application in the diagnosis of COVID-19 associated olfactory loss.
Simple and commercially available, the UPSIT is a reliable, practical test that has been administered internationally to more than 500,000 individuals. Its recent use in patients with COVID-19 has a foundation that harkens back to another viral pandemic more than 50 years ago.
“It’s been known since the 1930s that a major route of polio virus into the brain is through the olfactory pathways,” says Richard Doty, PhD, of Penn Medicine, inventor of the UPSIT.
Director of the Penn Smell and Taste Center in the Department of Otorhinolaryngology-Head and Neck Medicine, Dr. Doty has been studying the olfactory system—and the loss of smell in its relation to disease—for more than 45 years.
COVID-19, Anosmia, and Dysguesia
Loss of smell, or anosmia, and of taste (or dysguesia) were early findings of studies and anecdotal reports from China when COVID-19 emerged there, and have been noted since in the United States, South Korea, Italy, Iran and France, among other nations.
“We now know that almost everyone who has COVID-19 has some degree of smell loss, at least early in the disease process,” Dr. Doty, said in a recent interview. “And we know that the most common cause of smell loss in the general population, aside from COVID-19, is from [other] viruses.”
Smell and the Olfactory System
The sense of smell originates in the receptors of the primary olfactory neurons situated in the epithelium at the roof of the nasal vault behind and slightly above the nose. From the olfactory receptors, information is transmitted by the olfactory nerves to the olfactory bulb in the brain through the cribriform plate. From the bulb, this information enters the olfactory tracts beneath the frontal lob and is transmitted from there to other regions of the brain.
The sense of taste is closely allied with that of smell, sharing many of the same receptors, a characteristic that explains the blunting of taste when people get colds or other conditions that affect the nose. Loss of smell in COVID-19 may have implications beyond mere inconvenience. Dr. Doty has proposed that anosmia be considered a bio marker for diagnosis, and there is evidence that loss of smell may function as a prognostic indicator for the disease. Whether the olfactory system plays a role in the etiology of COVID-19, however, remains an intriguing mystery.
Smell Dysfunction: A Biomarker for COVID?19
Dr. Doty has been involved in a major study in Iran to measure loss of smell. Published in International Forum for Allergy and Rhinology in April, the study is a bellwether for objective studies of smell loss in COVID-19.
In this study, Dr. Doty and colleagues demonstrated that decreased smell function, though not always anosmia, is a major marker for SARS-CoV-2 infection. Notably, 98% of patients demonstrated some smell dysfunction. Fortunately, most individuals who lose their sense of smell to COVID-19 get it back within three to four weeks, a finding reinforced by studies initiated at the Perelman School of Medicine and elsewhere.
Around 25% of people with COVID-19, however, have long-lasting loss of olfactory function, according to Dr. Doty.
“We don’t know yet whether it’s permanent, though that is a possibility,” says Dr. Doty. He suggests that patients who have lost their sense of smell contact Penn ENT.