There is no worse fate for someone who loves food than losing their sense of smell. But it’s become an increasingly unfortunate reality for many who’ve had a bout of Covid-19 and are struggling with its persisting aftereffects. In fact, one recent study estimates that over 20 million Americans lost their sense of smell (or taste) in 2021 and that five million have only partially recovered or haven’t recovered at all.
Some individuals may experience the total opposite. Instead, their noses play tricks on them, smelling scents that aren’t actually there (phantosmia) or rendering everyday smells as disgusting, foul odors (parosmia). This can lead to a loss of appetite, nausea, vomiting, and an overall dip in one’s quality of life.
While some medical interventions, like antiviral drugs or smell training, can help regain a lost sense of smell, not everyone responds to them. However, a new noninvasive medical procedure involving a neck injection may change that.
Called stellate ganglion block, an anesthetic cocktail is injected into a cluster of nerves (called the stellate ganglion) that are part of the autonomic nervous system, which controls involuntary bodily functions like heart rate and sweating. Researchers at Jefferson Health in Philadelphia tried the procedure on 37 people with parosmia, 22 of whom reported noticing a normal sense of smell returning one week after the injection. Eighteen of these 22 individuals reported significant improvement within one month. After three months, there was a mean of 49 percent improvement among the initial 22.
These findings will be presented next Monday at the annual meeting of the Radiological Society of North America.
“The initial patient had a tremendously positive outcome, almost immediately, with continued improvement to the point of symptom resolution at four weeks,” Adam Zoga, professor of musculoskeletal radiology at Jefferson Health who led the study, said in a press release. “We have been surprised at some outcomes, including near 100 percent resolution of phantosmia in some patients, throughout the trial.”
A loss or alteration in smell can happen with other viral infections too, like the common cold, but it usually resolves quickly. Scientists still aren’t sure why with Covid-19, it continues once the infection clears, but they have a few theories. It may be due to ongoing inflammation in the nose, which diminishes the number of olfactory sensory neurons there, or it genetically rewires them so that smell signals can’t get to the brain.
The procedure has been used before to alleviate smell issues linked to long Covid, demonstrating significant success in small-scale trials. The new study is the largest trial to date. It involves using a CT scan or ultrasound to guide the injection to the stellate ganglion at the base of the neck. This needs to be done very precisely and carefully since there are major blood vessels there delivering vital blood to the brain. Stellate ganglion block has also been used to treat other conditions like cluster headaches, phantom limb pain, and cardiac arrhythmia.
The anesthetic cocktail includes a small dose of corticosteroid as a salve for any inflammation within the nerves caused by any remaining coronavirus.
After the first injection, 26 participants came back for a second injection six weeks later. This injection was administered to the neck on the opposite side of the initial injection. Eighty-six percent of individuals who experienced relief with the first treatment also reported an improved sense of smell with the second.
Why exactly this injection works for some people but not others is unclear. It’s important to note that in the new study, individuals who didn’t respond to the first round of injections also didn’t respond to subsequent second rounds, meaning it's clear it simply doesn’t work for everyone.
The procedure, however, does offer hope for some people living with the upsetting and often debilitating effects of an altered sense of smell. It also invites scientists and clinicians to further investigate stellate ganglion block or other similar ways of treating parosmia and phantosmia. (One clinical trial for the procedure is currently recruiting volunteers.)
