Patients with long COVID who experience loss of smell could benefit from a minimally invasive surgical procedure that involves an anesthetic shot deep inside the neck, a new study has found.

According to the study, which will be presented next week at the annual meeting of the Radiological Society of North America, using an image-guided minimally invasive procedure that takes less than 10 minutes, patients could alleviate symptoms of parosmia, a condition characterized by a distorted sense of smell.

Parosmia occurs after bacterial or viral infections, head trauma, neurological conditions and COVID-19. Symptoms include trouble detecting certain smells, a sense of persistent foul odor especially with food, and a feeling that certain pleasant smells are overpowering and unbearable.

Researchers estimate that around 60% of COVID-19 patients experience parosmia. Although most people recover from the condition over time, in some patients with long-term COVID-19, the symptoms might even last for years, affecting their appetite and day-to-day life.

"Post-COVID parosmia is common and increasingly recognized. Patients can develop a distaste for foods and drinks they used to enjoy," said the study's lead author, Dr. Adam C. Zoga, from Jefferson Health in Philadelphia.

The study looked at the potential benefits of CT-guided stellate ganglion block, an injection of anesthetic medication into stellate ganglia, the nerves on one side of the neck. These nerves are part of the autonomic nervous system responsible for regulating involuntary processes such as heart rate, blood pressure, breathing and digestion.

"The minimally invasive procedure takes less than 10 minutes, and no sedation or intravenous analgesia is necessary," the researchers said.

The treatment technique is currently used for conditions like cluster headaches, phantom limb pain, Raynaud's and Meniere's syndromes, angina, and cardiac arrhythmia.

The trial involved 54 patients referred by an ear, nose and throat specialist. All of them had at least six months of post-COVID parosmia without any signs of improvements through pharmaceutical and topical therapies.

The injection into the stellate ganglion was administered using a spinal needle placed at the base of the neck using a CT scan. A corticosteroid was also injected along with the anesthetic, as the COVID-19 virus might have caused nerve inflammation.

"The initial patient had a tremendously positive outcome, almost immediately, with continued improvement to the point of symptom resolution at four weeks. We have been surprised at some outcomes, including near 100% resolution of phantosmia in some patients, throughout the trial," Dr. Zoga said.

Out of 37 patients followed up after the trial, 22 (59%) reported improved symptoms in a week.

"Of these 22, 18 (82%) reported significant progressive improvement by one month post-procedure. At three months, there was a mean 49% improvement in symptoms (range 10% to 100%) among the 22 patients," the researchers wrote.

A second injection on the other side of the neck was given to 26 patients at a six-week interval. The results showed that in those patients who did not have improvements with the first injection, the second injection was also not effective. However, 86% of patients who showed improvements after the first injection had additional improvement with the second injection. No complications or adverse events were reported, researchers said.

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