The Effects of SARS-CoV-2 Infection on the Cognitive Functioning of Patients with Pre-Existing Dementia.

Background: Cognitive postscripts of COVID-19, codenamed as 'cognitive COVID' or 'brain fog,' characterized by multidomain cognitive impairments, are now being reckoned as the most devastating sequelae of COVID-19. However, the impact on the already demented brain has not been studied. Objective: We aimed to assess the cognitive functioning and neuroimaging following SARS-CoV-2 infection in patients with pre-existing dementia. Methods: Fourteen COVID-19 survivors with pre-existing dementia (four with Alzheimer's disease, five with vascular dementia, three with Parkinson's disease dementia, and two with the behavioral variant of frontotemporal dementia) were recruited. All these patients had detailed cognitive and neuroimaging evaluations within three months before suffering from COVID-19 and one year later. Results: Of the 14 patients, ten required hospitalization. All developed or increased white matter hyperintensities that mimicked multiple sclerosis and small vessel disease. There was a significant increase in fatigue (p = 0.001) and depression (p = 0.016) scores following COVID-19. The mean Frontal Assessment Battery (p < 0.001) and Addenbrooke's Cognitive Examination (p = 0.001) scores also significantly worsened. Conclusion: The rapid progression of dementia, the addition of further impairments/deterioration of cognitive abilities, and the increase or new appearance of white matter lesion burden suggest that previously compromised brains have little defense to withstand a new insult (i.e., 'second hit' like infection/dysregulated immune response, and inflammation). 'Brain fog' is an ambiguous terminology without specific attribution to the spectrum of post-COVID-19 cognitive sequelae. We propose a new codename, i.e. 'FADE-IN MEMORY' (i.e., Fatigue, decreased Fluency, Attention deficit, Depression, Executive dysfunction, slowed INformation processing speed, and subcortical MEMORY impairment).