Olfactory dysfunction can be from viral-induced olfactory nerve damage, local inflammation and damage to the supporting cells and sinonasal epithelium, or both. —Jennifer Villwock, MD
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August 2021
Parosmia and Phantosmia
For those who do recover their sense of smell, the recovery isn’t always easy and can often be accompanied by parosmia and/or phantosmia. Both conditions have gained a lot of attention in connection with COVID-19, according to Bradley J. Goldstein, MD, PhD, an associate professor in the departments of head and neck surgery and communication sciences and of neurobiology at Duke University School of Medicine in Durham, N.C.
“In a recent European study, parosmia was present in 28% to 59% of COVID-19 patients who had olfactory loss,” Dr. Goldstein said. While not everyone with smell loss will also develop parosmia, Dr. Goldstein added that it isn’t well understood why parosmia is so prominent in post-COVID-19 subjects and what exactly is causing it.
In COVID-19 and non-COVID-19 cases alike, parosmia and phantosmia often occur months after the initial illness or injury, Dr. Holbrook said. Phantosmia can occur during recovery from smell loss related to traumatic brain injury, for example, or can also be caused by seizures or migraines.
“As the regenerating nerves are finally making their way to connect into the olfactory bulb, which is the first brain structure that the nerves in the nose connect with, those nerves are not targeting back to the same spot that they did before,” Dr. Holbrook said. “So, the wiring is a little altered, and that alteration gives the experience of distorted smell.”
The distortion, unfortunately, does not lean toward scents like baking bread or fragrant roses. Common descriptors liken it to cigarette smoke, mold, rot, vomit, and sewage. And odors that may have previously smelled good to the patient, like coffee or their significant other, can trigger a really bad smell, which may cause a great deal more anxiety than smell loss alone. “For the patient, this isn’t promising, but since it can be a sign of recovery, a lot of us consider it a good thing,” said Dr. Holbrook.
For the patient, scent distortion isn’t promising, but since it can be a sign of recovery, a lot of us consider it a good thing. —Eric Holbrook, MD
Parosmia and phantosmia generally aren’t as well studied as anosmia or hyposmia, a loss of or a decreased sense of smell. This is also true in the setting of COVID-19. In Dr. Villwock’s practice, the majority of her patients who have survived COVID-19 will express some degree of parosmia and/or phantosmia and commonly describe it as “wet dog,” “moldy cigarette,” or some other “weird, bad smell.” It often seems unprovoked but can be triggered by exposure to an odorant, she said, and some have it constantly, while for others it’s intermittent.
“In my practice, patients are more likely to have these issues if they have some residual olfactory function,” Dr. Villwock said. “Prior to COVID-19, this was a phenomenon I was frequently seeing in my patients with persistent olfactory dysfunction from other viruses. Parosmia and/or phantosmia most commonly occurred during the first 12 months following the virus onset and usually lasted a few months before resolving itself.”
If patients visited her within that first year of smell loss, she would always counsel them about the possibility of developing parosmia and phantosmia. While she didn’t have a way to predict who would get it, she wanted them to be aware of the conditions so that they would not panic if either one developed.
Dr. Yan said that in her experience, parosmia typically occurs two to three months after COVID-19 patients have experienced their initial smell loss or had a COVID-19 diagnosis, and it seems to be more common in female patients. “Many people will say that they feel as though they’ve recovered somewhat in terms of their sense of smell,” she said, “and then a very sudden, abrupt light switch goes on and they realize their sense of smell has become completely distorted,” Dr. Yan said.