An Experimental Treatment Could Help COVID Smell Distortion

Smell loss, or anosmia, is a well-known symptom of COVID. Some people don’t experience full-blown loss but rather changes in or distortion of smell, a condition known as parosmia. Studies estimate that between 25 and 75 percent of those with a COVID infection experience long-term parosmia. Now an injection that blocks nerve pain could potentially provide relief for some people.

The technique, known as a stellate ganglion block, has been used for decades to treat all sorts of pain conditions. During the procedure, specialists inject a local anesthetic into a collection of nerves in the neck to block their activity and thereby reduce pain. Sometimes people receive two injections, which are administered a few days apart on each side of the neck. Now some individuals with long-COVID-induced parosmia are electing to have the procedure, and many of them have reported benefits in early studies. But the procedure remains somewhat unproven, experts say.

Parosmia can be detrimental to a person’s well-being. For many with the condition, food has very weird smells and tastes. Cheryl Lezak, a 52-year-old who developed parosmia after a COVID infection in December 2021, describes food as smelling like burned metal and tasting of phlegm.

“It’s like being in hell,” she says, noting that she ended up using nose plugs in order to eat certain foods. “It’s just devastating, and it interrupts your life so much. You don’t realize how important [the smell of] food has become or was. You take that for granted.”

In addition to being disruptive to day-to-day function, COVID-induced parosmia is linked to anxiety, depression and suicidal thoughts.

Prior to the pandemic, some research investigated using stellate ganglion blocks for smell-related disorders. As the prevalence of these conditions has increased with COVID, the body of research has grown. Researchers at Jefferson Health in Philadelphia presented some of the most recent findings on the treatment’s effectiveness in late November at a Radiological Society of North America conference. In a sample of 54 people, 86 percent of those who reported some improvement after the first injection also reported additional improvement after a second injection. None of the participants reported complications or adverse events. The findings have not yet been published in a scientific journal.

“More than 60 percent of people who have parosmia symptoms after COVID have experienced at least 50 percent relief from the symptoms after one injection,” says Adam Zoga, the study’s lead author and a professor of musculoskeletal radiology at Jefferson Health. “Most patients are getting significant improvement.”

Zoga’s team is not the only group of researchers working to evaluate whether stellate ganglion block works for smell distortion caused by COVID. There have been other case studies and surveys that have suggested the treatment’s effectiveness. Some pain specialists have carved out a niche for themselves by offering the procedure to treat COVID-related parosmia and potentially other lingering symptoms. In Bryan, Tex., the clinic Republic Pain Specialists administers about 25 stellate ganglion blocks a day, and one of its specialists, David Gaskin, has also published research on the treatment’s high success rate.

Personal anecdotes reflect a mix of experiences. Lezak says that although she had a small improvement after the first injection, the second one did nothing. But James Naylor, a 37-year-old in the U.K., who has had parosmia since a probable COVID infection in early 2023, got the block in early October and has seen his smell improve in the past couple of months. “For me, it wasn’t the case [that] it got cleared up instantly,” he says. “I’ve been recovering gradually since.” Naylor notes that he never tested positive for COVID, though.

The procedure is reasonably safe if it is performed by an experienced specialist, although it is not without risks. Accidentally injecting the block into an artery can be fatal. This risk can be greatly reduced with the help of imaging. But there are still some unknowns.

“We don’t know how long the effects are going to last,” Zoga says. “The first patient [from the Jefferson Health cohort] is 20 months out, and she has had no recurrence of symptoms.” Others who had a positive response to the treatment have not had recurring symptoms either. “But to date I can’t say that three years after the injection, the symptoms won’t come back,” he says.

The mechanism for how the treatment works is unclear. “No one could explain to me how it could possibly work,” says Nyssa Farrell, an assistant professor of otolaryngology at Washington University in St. Louis. “But the one thing that was consistent [was that] we were hearing patients say, ‘We tried it, and for the first time in months, I could smell and taste normally.’”

Zoga thinks the mechanism might have to do with the way SARS-CoV-2, the virus that causes COVID, infects the body. A growing body of evidence suggests the virus causes inflammation of the nerves that leads to post-COVID symptoms, and the block may be reducing that inflammation. Farrell also highlights that parosmia likely involves a central nervous system processing change in which the nerves remain functional, indicated by the fact that people with parosmia can detect odors, but the inflammation causes a “miswiring” so that smell signals are distorted when they come to the brain.

Many insurance companies are hesitant to reimburse people for the procedure, however. While Zoga says he was able to get his patients’ insurance to cover the stellate ganglion block by listing it as a peripheral nerve injection, Gaskin’s patients primarily pay out of pocket. Gaskin charges $500 for each injection, so if one of his patients opts to receive it on both sides of their neck, they will looking at a bill of $1,000 for the procedure alone. Naylor says he paid £2,500 (about $3,000) for his two injections.

Randomized controlled trials—which are considered the gold standard for medical research because they compare a control group with a treatment group—are important to fully assess the procedure and convince insurance companies that it is worth reimbursement. Farrell and her team are currently recruiting for one such study in which people who have had parosmia for at least six months and report it as “bothersome” will receive either a stellate ganglion block or a placebo injection and be evaluated for improvement.

“If it’s not controlled, you just don’t know,” Farrell says. “There’s always a placebo effect, and you don’t want to negate that placebo effect—it’s a great effect to have. But at the same time, if it’s just placebo that’s causing these changes, do you really want to take the risk of putting a needle in your neck?”