In a recent study, researchers investigated the blood-brain barriers (BBB) damage due to cognitive dysfunction brought on by long-COVID. 

The study included both long-term COVID patients and recovered COVID-19 individuals irrespective of cognitive impairment. Serum samples were also examined for inflammatory markers and BBB impairment.

The rapid smell identification test (Q-SIT) olfactory testing, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), lung imaging, and haematological parameters of eligible subjects were evaluated at the time of diagnosis of COVID-19 and 146 days following the infection.

Results showed a significant increase in Interleukin (IL)-8 levels in mild instances and an increase in IL-6, IL-8, and tumour necrosis factor (TNF) in severe COVID-19 cases. A substantial increase in the serum concentrations of IL6, IL8, TNF, and S100 was also observed in cases with brain fog. Anosmia was seen in 50% of the subjects. The Montreal Cognitive Assessment (MoCA) test revealed abnormalities in executive function, recollection, and word finding in nearly six subjects with mild to severe cognitive dysfunction.

In COVID-19 patients with brain fog, DCE-MRI imaging revealed noticeably increased whole-brain leakage. An increase in the proportion of brain volume with leaky blood vessels in the brain fog group was also seen. Patients with long COVID, with brain fog, showed noticeably higher BBB permeability compared to patients who had recovered and had lengthy COVID without brain fog. A noticeable increase in leakages in the left and right frontal brain and the left and right temporal lobes was also seen.

Macrostructure comparisons between individuals with brain fog and those who had recovered showed smaller overall brain volumes and significantly smaller volumes of cerebral white matter in both hemispheres. A decreased volume of cerebellar white matter was noticed among individuals with extended COVID, those who had recovered, and those with brain fog. The volume of cerebrospinal fluid (CSF) only increased noticeably in the brain fog group.

The studys results demonstrated a link between long-lasting COVID "brain fog" and BBB malfunction as well as higher levels of systemic inflammation and BBB dysfunction indicators. The study also showed that BBB impairment was exclusive to patients with brain fog and could still be present a year after recovering from COVID-19 infection.

(Study: https://www.news-medical.net/news/20230127/Disruption-of-the-blood-brain-barrier-due-to-long-COVID.aspx)