Whether from birth or developed later in life, the absence of smell has never gotten much attention — at least until the onset of the COVID-19 pandemic. Loss of smell is one of the most common side effects of COVID-19. While most COVID-19 infected patients eventually recover their sense of smell, there are those who have yet to have it return. For an unfortunate few, it turns out that their all-important sense of smell may never return.
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Anosmia is the medical term for a complete absence of smell, while hyposmia refers to a partial loss of smell. To better understand anosmia — including its causes, treatments and relationship to COVID-19 — we spoke to rhinologist Raj Sindwani, MD.
Viruses, ranging from the common cold to COVID-19, are one of the leading causes of an acquired loss of smell. Dr. Sindwani says, “There’s a risk of temporary and, less commonly, permanent loss of smell with any viral infection.”
Short-term loss of smell in this setting is usually from congestion or inflammation in the nose. “Things get swollen and the odors just are not getting to the smell receptors that live high in the nose,” he says. “It happens with the common cold and it frequently happens early in COVID-19 cases as well.”
With longer-term cases, that stretch on for months or even permanently, he says the issue may be damage to the smell receptors or olfactory nerves themselves. “That’s what we think when we look at a CT scan or an MRI and don’t see any physical signs of congestion or appreciable physical change,” he says. “We can’t see the damage on those images, that inability to receive those smells.”
“Depending on what we see or don’t see on examination,” he continues, “we will sometimes do imaging (like a CT scan or even an MRI) to see if there’s anything anatomic that can explain why these smell receptors aren’t working. We will also check to see if there’s anything more sinister going on, like a nose or brain tumor.”
As for viral causes, the loss of smell has become one of the predominant symptoms of positive COVID-19 cases, although the exact cause remains unknown. “We just have the current data to go on,” Dr. Sindwani says, “and we know it’s happened before from viral infections.”
He says that there is a range of data points available but up to 80% of COVID-19 patients experience some sort of subjective disturbance in their sense of smell.
But, for long-term smell loss, that number is actually much smaller. “One study used objective smell testing and found that only 15% of COVID-19 patients experience a loss of smell for more than 60 days and less than 5% experienced it for longer than six months. That’s is really comforting news,” Dr. Sindwani notes.
One more potential wrinkle that deserves more research, he says, is the previously mentioned study which also posited that COVID-19 patients who lose their sense of smell have milder cases than those that don’t. “It was based on retrospective data, but patients who maintained normal smell function were more likely to have a more severe course of the disease, including being more likely to be hospitalized and even intubated,” he says.
With post-viral issues – as well as with other occurrences caused by chronic sinusitis, aging, Parkinson’s, trauma and, occasionally, congenital cases – Dr. Sindwani says that steroids, either by mouth or topical nasal steroids, can also work.
“Data is lacking on this, but the thought is that these steroids can reduce inflammation in parts of the nasal cavity or in these smell receptors which are inflamed,” he says.
Nasal polyps and chronic sinusitis (recurrent or persistent sinus infections) are the most common problems, he says, noting there are treatment options, including surgery, for those issues. Whether it’s medication or surgery, there are options. “We treat what we know at first,” says Dr. Sindwani. “If it’s polyps or a sinus tumor, those have their own specific treatments. The loss of smell is actually a symptom of the problem.”
He also notes that, while there’s still plenty of research left to do on anosmia treatment, there’s been recent interest in how consuming omega-3 fatty acids and other supplements could help the sense of smell recover.
But what if your patients could train themselves to smell again? That’s the thinking behind olfactory training and it would be worth trying even for COVID-related smell loss. “The idea is that it’s an extremely safe, self-driven treatment option with no side effects that’s been helpful, including in post-viral cases of smell loss,” Dr. Sindwani says.
“It utilizes what’s called the odor prism,” he continues. “It uses primary odors to retrain the nose, relying on memory and experience, to train those nerves to come back to life.”
Just as there are primary colors (red, blue and yellow), there are thought to be primary smells and each has a corresponding example that is typically used to represent it: flowery (rose), fruity (lemon), aromatic (cloves or lavender) and resinous (eucalyptus).
“With these four primary smells, we ask the patient to take each smell, usually in the form of an oil or scent stick, put it under their nose and deeply inhale that scent for 15-to-20 seconds,” Dr. Sindwani explains. “And while you’re inhaling, they intentionally try to think about and remember what roses smell like and even look like. They want to mentally immerse themselves in the thought, picture the roses and what they would smell like.”
The idea, he says, is that the patient is combining that visual imagery with the stimulation of an isolated scent to retrain your nose on how to smell.
After going through the process with that flowery scent, the patient repeats the same steps with the other three scents. “Again, you’re trying to conjure up what that object looked like and smelled like to retrain those smell receptors back into working,” he adds.
The exercise is repeated two-to-three times a day for a while and, he says, it’s possible for patients to get a sustained improvement in their sense of smell at three months, six months and even up to a year. In some situations, steroid sprays might be used, too, to cause an even better improvement.