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Advanced Neurologyurology
Advanced Ne Neurological complications of COVID-19

headache, memory decline, cerebrovascular event, and mild COVID-19 (89%) underwent a complete resolution
taste and smell disorders. In this review, we summarize the or improvement of olfactory and gustatory functions .
[4]
neurological complications in COVID-19 patients and the According to another study, the recovery time of infected
underlying mechanisms, which might help facilitate early adolescents aged 10–19 years varied from 2 days to 2 weeks,
diagnosis and early treatment so as to improve prognosis with an average of 5.7 days . Besides, it has been reported that
[15]
of COVID-19 patients. 12% of smell disorders preceded the onset of other symptoms,
22% of these disorders occurred in conjunction with other
2. Neurological complication of COVID-19 symptoms, and 65% occurred after other symptoms .
[16]
2.1. Alterations in taste and smell However, at present, the mechanism of smell and taste
The loss or diminished senses of taste (ageusia) or smell disorders in patients with COVID-19 is still not clearly
(anosmia) are the frequent symptoms and the early defined. Angiotensin-converting enzyme 2 (ACE2)
[17]
neurologic manifestations in COVID-19 patients . The receptors are functional receptors of SARS-CoV-2 ;
[3]
occurrence rate of these symptoms is reported to range therefore, the olfactory epithelium cells, which have
between 38% and 74% across different cohorts [4-8] . In high ACE2 expression, become easily infected by SARS-
addition, in a multicenter study, around 38% and 41% CoV-2 . Anosmia is caused by the injury of olfactory
[18]
of mildly infected patients have been reported to show epithelium, instead of sensory neurons. Furthermore,
gustatory and olfactory impairment, respectively . there is a positive correlation between olfactory and
[7]
Further, a meta-analysis of 15 studies consisting of a total gustatory disorders . Most COVID-19 patients gradually
[19]
of 3739 participants with confirmed COVID-19 reported recover from olfactory and gustatory disorders, and some
that around 1354 and 1729 of infected patients showed interventions such as olfactory training may be helpful
symptoms of taste and smell impairment, respectively . during the recovery process . The interventions for loss
[9]
[20]
The similar study also demonstrated that the loss of taste of taste are less common and deserve more investigations.
and smell occurred in 49.0% (95% confidence interval
[CI] 34.0–64.0) and 61.0% (95% CI 44.0–75.0) of the 2.2. Brain function decline
COVID-19 patients, respectively. Another meta-analysis The COVID-19 affects the brain functions, such as
on patients in North America reported that the rate of taste cognitive ability and consciousness, in a variety of ways,
disorder was 38.6% (95% CI 7.9–75.3), while the rate of which result in acute and long-term effects on the infected
smell disorder was 54.5% (95% CI 39.3–69.3), and around individuals. Acute brain dysfunctions include delirium,
5977 patients manifested symptoms of both smell and taste coma, confusion, and somnolence. It has been reported
disorders, accounting for 31.3% of the patients (95% CI that delirium was present in 81.7% of COVID-19 patients
13.6–52.2) . Taken together, the loss of smell and/or taste admitted to intensive care units . In addition, these acute
[10]
[21]
is a common neurologic symptom of COVID-19 patients. symptoms are associated with higher risk of long-term
[22]
However, the occurrence rate of smell and taste cognitive decline , which explains why longitudinal studies
disorders in COVID-19 patients varies among different on long-term changes in cognitive function have attracted
populations as well as gender and age groups. Compared much attention. In a longitudinal study of 3232 COVID-
with male COVID-19 patients, female patients were 19 patients in China, it was found that the occurrence rate of
more likely to have trouble in smelling and tasting . cognitive impairment in COVID-19 survivors was 12.45%
[11]
On the contrary, another study reported that gender did after 12 months. The cognitive function of severe patients
not significantly influence the olfactory and gustatory was lower than that of non-severe patients and control
[23]
function in patients . In addition, younger people have group . High risk of the early-onset (95% CI 3.30–7.20)
[12]
been reported to have more severe smell disorders and take and late-onset (95% CI 3.58–16.03) cognitive impairment
longer time to recover . It is worth noting that in a study on was associated with severe COVID-19. Another follow-up
[8]
841 COVID-19 patients, olfactory and gustatory disorders study on home-isolated COVID-19 patients reported that
were more common in patients with mild COVID-19 , around 44% of young patients had cognition impairments,
[13]
suggesting that olfactory and gustatory changes may be an such as memory problems and impaired concentration,
important marker for the early disease diagnosis. 6 months after infection, which were associated with
increased convalescent antibody titers, indicating the
The recovery of smell and taste disorders in the infected [24]
patients is another concerning topic. The recovery time of severity of underlying disease .
the olfactory and gustatory disorder depends on the severity The reduction in brain function caused by COVID-19 is
of COVID-19 and the disorders themselves . A follow-up governed by a number of factors, such as lung damage and
[14]
study reported that after 4 weeks of infection, patients with the resulting hypoxemia caused by COVID-19. It has been

Volume 1 Issue 2 (2022) 2 https://doi.org/10.36922/an.v1i2.83