In a recent study published in the journal diagnosis, Researchers are investigating the relationship between olfactory dysfunction associated with coronavirus disease 2019 (COVID-19) and subsequent neurocognitive impairment.
study: A comprehensive review of olfactory dysfunction associated with COVID-19: elucidating the association with neurocognitive impairment and magnetic resonance imaging findings. Image credit: Maria Boiko / Shutterstock.com
background
Acute anosmia is one of the earliest and most common symptoms associated with COVID-19, with an incidence of up to 75%. Manifestations of both olfactory and gustatory dysfunction in COVID-19 range from decreased or distorted perception to complete loss of smell and/or taste.
In the context of COVID-19, acute anosmia is defined as a change in the sense of smell that persists for less than 14 days. Anosmia typically occurs around the third day after initial infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and odor perception completely resolves within 4 to 6 weeks. However, up to 27% of patients with COVID-19 continue to experience changes in their sense of smell for up to four months, and 21.3% of patients report changes in their sense of smell for up to one year.
In addition to COVID-19, various other viral infections can cause anosmia, in addition to secondary effects of trauma, neurodegenerative pathological processes, and sinus diseases. there is. Despite the high prevalence of COVID-19-related anosmia, including conditions that can affect the olfactory bulb (OB), olfactory sulcus (OS), olfactory fissure, and olfactory tract (OT) , few studies have discussed the neuroimaging abnormalities associated with this condition. ).
About research
In this study, researchers conducted a literature review of OB changes observed in patients with clinically confirmed anosmia after diagnosis of novel coronavirus disease (COVID-19). They also discussed current treatments for anosmia associated with COVID-19.
To achieve this objective, the researchers will continue to research the novel coronavirus disease (COVID-19), olfactory disorders, olfactory disorders, image processing, and We searched multiple databases including PubMed, Scopus, and Google Scholar using keywords such as “SARS-CoV-''. 2'', “Magnetic Resonance Imaging (MRI)'', “Olfactory Bulb'', “Neurocognitive Disorders'', “Mood Disorders'', “Neuropsychiatric Sequelae'', “Treatment''. This search resulted in a total of 12 observational studies and 1 case report included in the analysis.
How does SARS-CoV-2 cause anosmia?
SARS-CoV-2 is thought to be neurotropic, neuroinvasive, and neurovirulent, with some virus variants having a higher tropism for the central nervous system (CNS) than others. Related. In particular, the ancestral His D614G strain, followed by the gamma, delta, and omicron BA1 variants, are associated with the greatest neurotropism in descending order.
Despite several studies assessing the impact of SARS-CoV-2 infection on the sense of smell, the exact etiology and molecular mechanisms responsible for this dysfunction remain unclear. Some of the proposed hypotheses include mechanical obstruction due to congestion or rhinitis, which may impair airflow and transport of odorants for odor perception. However, anosmia often lasts longer than respiratory symptoms, and many COVID-19 patients experience it without the associated nasal congestion needed to support this theory. Several studies have found that this hypothesis has been disproved.
Researchers also hypothesize that SARS-CoV-2 causes direct damage to olfactory neurons, subsequently causing olfactory dysfunction. Despite the absence of both angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) in olfactory neurons, both of which are important for viral cell entry, SARS-CoV-2 Other pathways may be used to infect the olfactory system (BSG), neuropilin-1 (NRP1), TMPRSS11A, and furin receptors, causing dysfunction.
MRI images reveal olfactory dysfunction in new coronavirus infection
The reviewed studies include several MRI findings in patients with COVID-19, including OB volume abnormalities and signal intensity changes, OS depth changes, abnormalities within the olfactory cortex, and neuronal fiber irregularities. Contains a description of.
Measurement of OB volume (OBV) and OS depth are the most common approaches to assess the olfactory system. To this end, several studies have observed a decrease in OBV and OS depth on both the right and left sides of hospitalized COVID-19 patients, indicating that SARS-CoV-2 is in the olfactory neural pathway. has been suggested to cause direct damage.
Up to a third of patients who recover from COVID-19 report neurological symptoms, including brain fog, insomnia, headaches, depression, anxiety, and mental fatigue. In COVID-19, long-term olfactory impairment is associated with severe cognitive consequences, which may be due to inflammation, altered neurogenesis in the olfactory system, and functional changes within brain structures.
Treatment of olfactory dysfunction caused by the new coronavirus infection
Although anosmia in patients with COVID-19 often resolves on its own, a significant proportion of these patients experience chronic anosmia. Therefore, a wide range of therapeutic approaches have been proposed to treat COVID-19-related anosmia, including corticosteroids, intranasal insulin, various supplements in the diet, and olfactory training.
Future studies are needed to determine the effectiveness of combining these treatment strategies to restore olfactory function.
Reference magazines:
- Simonini, L., Frisia, F., Ait Ali, L., other. (2023). A comprehensive review of COVID-19-associated olfactory dysfunction: elucidating the association with neurocognitive deficits and magnetic resonance imaging findings. diagnosis 14(4); 359. doi:10.3390/diagnostics14040359