The research, published in the Journal of Alzheimer's Disease Reports, found that participants with all subtypes of dementia experienced rapidly progressive dementia following infection with SARS-CoV-2.

Insights into the impact of Covid-19 on human cognition has so far remained unclear, with neurologists referring to it as "brain fog." The researchers investigated the effects of Covid-19 on cognitive impairment in 14 patients with preexisting dementia who had suffered further cognitive deterioration following the infection with SARS-CoV-2.

The patients included four with Alzheimer's disease, five with vascular dementia, three with Parkinson's disease, and two with the behavioral variant of frontotemporal dementia.

They were recruited out of a total of 550 patients with dementia who attended the wards of Burdwan Medical College and Hospital, Bangur Institute of Neurosciences, and private cognitive specialty clinics in West Bengal, between May 2013 and September 2022.

The researchers found that the characteristics of a particular type of dementia changed following Covid-19, and both degenerative and vascular dementias started behaving like mixed dementia. A rapidly and aggressively deteriorating course was observed in patients having insidious onset, slowly progressive dementia, and who were previously cognitively stable, they said.

Cortical atrophy, which causes the loss of brain cells, was also evident in the study's subsequent follow-ups, according to the researchers. Coagulopathy involving small vessels and inflammation, which were further correlated with white matter intensity changes in the brain, was considered the most important pathogenetic indicator, they said.

The rapid progression of dementia, the addition of further impairments of cognitive abilities, and the increase or new appearance of white matter lesions suggest that previously compromised brains have little defence to withstand a new infection. "Brain fog is an ambiguous terminology without specific attribution to the spectrum of post-Covid-19 cognitive sequelae," said study lead investigator Souvik Dubey, from Bangur Institute of Neurosciences.

"Based on the progression of cognitive deficits and the association with white matter intensity changes, we propose a new term: 'FADE-IN MEMORY' (Fatigue, decreased Fluency, Attention deficit, Depression, Executive dysfunction, slowed INformation processing speed, and subcortical MEMORY impairment)," Dubey said.

The researcher noted that as the ageing population and dementia are increasing globally, pattern recognition of Covid-19-associated cognitive deficits is urgently needed to distinguish between Covid-19-associated cognitive impairments and other types of dementia. "This understanding will have a definitive impact on future dementia research," ?Dubey added.