The search strategy will be performed to enhance methodological transparency and improve the reproducibility of the findings, following the PRISMA checklist ( Moher et al., 2015). This study aimed to determine any relationship between COVID-19 and cognitive complaints, such as dementia, mild cognitive impairment (MCI), or subjective cognitive decline (SCD). Therefore, it is crucial to identify whether COVID-19 possible neurologic lesions are associated with more significant cognitive impairment. It represents individuals with cognitive complaints without objective evidence of cognitive impairment ( Jessen et al., 2014). Besides these conditions, subjective cognitive decline is a condition before MCI and a possible dementia precursor. Also, a minor injury burden emerges when MCI represents a stage before AD, which is theoretically susceptible to medicating action ( Petersen et al., 2006). Neuropathological alterations of amnestic MCI are intermediate between normal individuals and those with Alzheimer's disease, involving tau protein neurofibrillary tangles, beta-amyloid deposits, and neurodegeneration. The prevalence of mild cognitive impairment (MCI) is 12–18% among adults over 65 years of age, and the annual progression rates from MCI to AD are 10–15% ( Ding et al., 2015). Alzheimer's disease is the most common form of dementia and accounts for 50–70% of dementia cases ( Prince et al., 2015). This number is estimated to be around 74.5 million in 2030 and 131.5 million in 2050. Data from Alzheimer's Disease International (ADI) report 46.8 million people living with dementia worldwide in 2015. The growing population aging over the past few decades has been associated with increased cognitive disorders. This association is significant since the same allele confers a higher risk of sporadic Alzheimer's disease (AD) ( Poirier et al., 1993). Regarding cognitive manifestations pathophysiology, a more severe neurological manifestations in patients with APOE 4 allele of Apolipoprotein E has been described ( Lumsden et al., 2020). Moreover, different cognitive presentations have been described, such as encephalopathy associated with severe conditions ( Delorme et al., 2020) and akinetic mutism associated with frontal hypometabolism ( Cani et al., 2021).
Another study evaluated cognitive impairment in outpatients, using Mini-Mental State Evaluation (MMSE), Montreal Cognitive Assessment (MoCA), Hamilton Rating Scale for Depression, and Functional Independence Measure (FIM), finding 80% of cognitive impairment ( Alemanno et al., 2021). A Chinese study evaluated the cognition of 29 COVID-19 patients using digital questionnaires, relating cognitive complaints to high C-reactive protein levels during the disease's acute phase ( Zhou et al., 2020). Also, patients with severe disease were more likely to develop neurological disorders, especially disorders of consciousness, acute cerebrovascular disease, and musculoskeletal disease ( Mao et al., 2020).Īside from general neurological manifestations, cognitive impairment was evaluated in COVID-19 patients. In a study conducted in Wuhan, Hubei province, 36.4% of the patients presented some neurological manifestation, with central involvement being more common (dizziness, headache, altered level of consciousness, stroke, ataxia, and epilepsy). Of note, neurological manifestations in COVID-19 patients were demonstrated during the pandemic ( Wu et al., 2020). COVID-19 has a wide range of clinical manifestations ( Guan et al., 2019). COVID-19 was declared a pandemic by the World Health Organization on March 11, 2020, with high levels of contamination and mortality in China, Italy, and Spain, and later in other countries ( WHO, 2021).
In November 2019, an unknown cause outbreak of pneumonia in Wuhan, Hubei province, China, began to attract Chinese health authorities’ attention.
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