COVID-19 Fog Symptoms Are Associated with Brain Metabolism and Platelet-to-Lymphocyte Ratio—A Cross-Sectional Analysis of the COVMENT Trial Baseline Data

Background: Post-COVID-19 cognitive impairment, commonly referred to as “brain fog,” represents a significant clinical problem, yet its underlying mechanisms remain incompletely understood. New research indicates that long-term cognitive consequences of SARS-CoV-2 infection may result from chronic immunological dysregulation and neurometabolic changes. Objective: We aimed to assess the associations between cognitive performance, cerebral glucose metabolism, and inflammatory markers in patients with COVID-19 brain fog symptoms. Methods: This study included 47 patients with post-COVID-19 cognitive complaints enrolled in the COVMENT trial. Cognitive performance was assessed using the Montreal Cognitive Assessment (MoCA). Brain glucose metabolism was evaluated with FDG PET-CT, and inflammatory markers, including C-reactive protein (CRP), monocyte-to-lymphocyte ratio, neutrophil-to-lymphocyte ratio, eosinophil-to-lymphocyte ratio, and platelet-to-lymphocyte ratio (PLR), were measured. Correlation analyses, logistic regression, and ROC analysis were performed to explore relationships between these factors. Results: A lower score of the MoCA abstraction domain correlated significantly with lower FDG uptake in multiple brain regions, including inferior parietal lobules and precuneus. Among inflammatory markers, only PLR demonstrated significant associations with both brain metabolism and abstraction performance. Lower PLR values were associated with greater neurometabolic impairment, and PLR < 130.1 was associated with abnormal abstraction performance. Conclusions: Post-COVID-19 cognitive dysfunction can be associated with selective neurometabolic alterations in brain regions supporting abstract reasoning. PLR seems to be associated with both cognitive performance and regional brain metabolism, suggesting a potential link between chronic immune dysregulation and neurocognitive impairment in post-COVID-19.