Olfactory dysfunction (OD)- a decreased or altered sense of smell- is a common symptom of COVID-19 infection. A new study found the reason behind it.
Previously, scientists believed that the loss of smell in COVID-19 was due to inflammation and damage to the olfactory nerves. But, a new study gathered evidence from medical imaging, suggesting that the loss of smell is due to swelling and blockage of the passages in the nose that conduct smells.
For this study, scientists searched the medical literature for studies reporting changes in olfactory structures detected through imaging tests of patients with COVID-19.
The prevalence of an olfactory cleft abnormality was almost 16-times higher in patients with COVID-19 and olfactory dysfunction (63%) contrasted with controls (4%). The olfactory clefts give a pivotal channel to airborne molecules to reach sensory olfactory neurons that connect to the brain to enable a person to perceive smells.
Lead author Claire Jing-Wen Tan of the National University of Singapore said, “We think this is good news for patients who want to recover their sense of smell since these blockages are expected to resolve with time, while nerve damage in comparison would likely be more difficult to recover from. These findings may not fully account for those who suffer from prolonged olfactory dysfunction, however, further studies that evaluate patients in this group may provide more information.”
- Claire Jing-Wen Tan et al. Neuroradiological Basis of COVID-19 Olfactory Dysfunction: A Systematic Review and Meta-Analysis. DOI: 10.1002/lary.30078