COVID-19 is known to cause loss of smell in certain patients. While this symptom is generally temporary, approximately 10% of patients may suffer from it for 6 months or more.
Earlier research carried out by a team of researchers from INRAE and ENVA observed that the SARS-CoV-2 infected olfactory mucosa is invaded by immune cells leading to its destruction and prolonged inflammation. Based on these observations, the same team decided to assess the effectiveness of corticosteroids-known for their anti-inflammatory properties-in restoring the sense of smell [1] .
Their results support the existence of a direct link between the loss of smell caused by the virus and a decrease in the olfactory neuron population in the nasal mucosa [2] . In addition, they show that early treatment with dexamethasone, a commonly used corticosteroid, improves the recovery of olfactory abilities in animals.
The improvement of the olfactory capacities is associated with a reduction of the immunity cells in the mucosa, and an increased level of regeneration of the olfactory neuron population. These results suggest that the corticosteroid treatments currently used-which have not been very successful in the treatment of prolonged anosmia-could be more effective if prescribed early, at the onset of symptoms of loss of smell.
[2] The olfactory neurons found in the mucosa are in direct contact with the odours passing through the nose and are responsible for detecting odorous molecules.
Reference:
Laetitia Merle-Nguyen, Ophélie Ando-Grard, Clara Bourgon, Audrey St Albin, Juliette Jacquelin, Bernard Klonjkowski, Sophie Le Poder, Nicolas Meunier, Early corticosteroid treatment enhances recovery from SARS-CoV-2 induced loss of smell in hamster. Brain, Behavior, and Immunity, 2024, ISSN 0889’159 , https://doi.org/10.1016/j.bbi.2024.02.020 .
