Mechanism of Anosmia Caused by Symptoms of COVID-19 and Emerging Treatments

Abstract

The occurrence of anosmia, the loss or change in sense of smell, is one of the most common symptoms of COVID-19 experienced by almost 53% of those affected. Several hypotheses explain the mechanism of anosmia in patients suffering from COVID-19. This study aims to review the related mechanisms and answer the questions regarding COVID-19-related anosmia as well as propose a new strategy for treatment of long-term anosmia as a result of COVID-19 infection. This paper covers all of the studies investigating olfactory disorders following COVID-19 infection and explains the possible reasons for the correlated anosmia, including olfactory cleft syndrome, local inflammation in the nasal epithelium, early apoptosis of olfactory cells, changes in olfactory cilia and odor transmission, damage to microglial cells, effect on olfactory bulbs, epithelial olfactory injury, and impairment of olfactory neurons and stem cells. The key questions that arise in this field have been discussed, such as why prevalent anosmia is varied among the age categories and among sexes and the correlation of anosmia with mild or severe COVID-19 infection. The angiotensin-converting enzyme 2 receptor is a significant player in the mechanism of anosmia in COVID-19 patients. Based on current studies, a novel approach to treat long-COVID-19 with ongoing anosmia has been proposed. The fields of smart drug delivery, tissue engineering, and cell therapy provide a hypothesized strategy that can minimize the side effects of current treatments and support efficient recovery of the olfactory system.

Global Trends and Research Hotspots in Long COVID: A Bibliometric Analysis

“…(3) Maria Ines Mitrani et al found that amniotic fluid-derived extracellular vesicle biologic could be used to treat respiratory disorders [ 53 ]. (4) Najafloo R et al proposed a comprehensive approach for the treatment of anosmia [ 54 ]. (5) Luckos M et al used EEG neurofeedback to treat cognitive dysfunctions after long COVID-19 [ 55 ].…”

Graphene-Based Materials Prove to Be a Promising Candidate for Nerve Regeneration Following Peripheral Nerve Injury

“…Among these methods, autologous superficial cutaneous nerves are known as the gold standard for bridging the nerve gap (>30 mm); however, there are several drawbacks, including major surgical risks, autologous graft rejection, infection, donor shortage, and the likelihood of further surgeries [ 11 ]. Tissue engineering (TE) proposes a promising alternative approach to overcome the existing challenges in tissue regeneration [ 12 , 13 , 14 ]. To successfully achieve neural regeneration, various factors, including topographical, chemical, mechanical, and electrical cues, should be considered.…”

Neuroradiological Basis of COVID‐19 Olfactory Dysfunction: A Systematic Review and Meta‐Analysis

“…In the small minority of patients with persistent anosmia, delayed recovery may be secondary to severe olfactory epithelium inflammation causing scarring and impairment of regeneration, 65 or damage to the olfactory receptor neurons and stem cell neurons. 63 In post-viral anosmia due to non-COVID-19 infections, the small subset of patients who experience permanent olfactory loss was similarly found to have virus-induced sensory neuronal damage. 66 Currently, the clinical significance of olfactory cleft opacification in COVID-19-associated OD is not fully known.…”