A team of researchers may have found an effective treatment for one of the more common symptoms of long covid: a chronically changed sense of smell. In a small study, the team found that many patients improved after undergoing a minimally invasive procedure often used to treat pain and circulation problems. In some cases, people’s symptoms disappeared altogether.

People will often experience smell and taste changes as a result of having a respiratory infection, though it took some time for this to be widely recognized as a common symptom of covid-19. Anywhere from 30% to 80% of covid-19 sufferers can develop smell alterations. These include anosmia (a partial or full loss of smell), parosmia (a distorted sense of smell, such as having once-pleasant things smell foul), and phantosmia (smelling things that aren’t there).

Thankfully, smell-related changes caused by covid-19 are typically self-limiting and go away after a few weeks. But a noticeable percentage of people will continue to experience smell and taste problems for months or even longer. A November 2021 study estimated that up to 1.6 million Americans had developed covid-related chronic anosmia within the first two years of the pandemic, for instance. Other studies have suggested that chronic anosmia/parosmia is one of the most common symptoms of long covid.

Though there are possible interventions that might be able to prevent a permanent loss of smell if used early enough, such as smell training, there are no established treatments for covid-related chronic anosmia/parosmia. But in a new study set to be presented later this month at the annual meeting of the Radiological Society of North America (RSNA), researchers say that they may have found one.

The team decided to treat patients with a stellate ganglion block, a procedure in which local anesthetic is injected into a bundle of nerves located around the neck (the stellate ganglion). These nerves are part of the sympathetic nervous system, which in turn is part of the autonomic nervous system. The autonomic nervous system governs our body’s involuntary functions, while sympathetic nerves regulate our “fight or flight” response to stressful situations. The stellate ganglion is responsible for sending many of the sympathetic nerve signals to your head, neck, and arms.

Stellate ganglion blocks are commonly used to treat symptoms caused by nerve-related conditions, such as shingles, phantom limb pain, or certain types of migraines. The team theorized that these nerves might also play a role in people’s covid-related smell disturbances.

The study involved 54 patients diagnosed with post-covid parosmia who had been referred to the authors by ear, nose, and throat specialists. The patients were initially given a stellate ganglion block on one side of the neck, with a prior CT scan used to find the best position for insertion. The injection also included a small dose of steroids, which the researchers speculate might help relieve any nerve inflammation caused by the coronavirus.

The authors were able to follow-up with 37 patients who received the procedure. Of these, 22 patients (59%) reported an improved sense of smell one week after the injection, while 18 patients reported continued progress a month later. Twenty-six patients also returned for a second injection on the other side of the neck six weeks later, and most of those who improved after the first dose saw continued improvement after the second.

Overall, the average improvement in symptoms among the responders during the three-month period of the trial was 49%, though some people seemed to experience a complete recovery.

“The initial patient had a tremendously positive outcome, almost immediately, with continued improvement to the point of symptom resolution at four weeks,” said lead author Adam Zoga, professor of musculoskeletal radiology at Jefferson Health in Philadelphia, Pennsylvania, in a statement from the RSNA. “We have been surprised at some outcomes, including near 100% resolution of phantosmia in some patients, throughout the trial.”

The findings are based on a very small sample size and have yet to go through the typical peer-reviewed process. So they should be viewed with added caution for now. And even in the best possible light, it’s likely that stellate ganglion blocks will not be able to help everyone who’s lost their normal sense of smell due to covid-19. But given the lack of available options, this potential treatment certainly seems to be worth further investigation, the study authors say.

“Other treatments have failed to date,” Zoga said. “This injection is working.”