Brain fog of post-COVID-19 condition and Chronic Fatigue Syndrome, same medical disorder?
Azcue, N, Gómez-Esteban, J C, Acera, M et al. · Journal of translational medicine · 2022 · DOI
Quick Summary
This study compared brain fog and fatigue symptoms in people with ME/CFS and those recovering from COVID-19 to see if they might be the same condition triggered by different causes. Both groups showed similar problems with fatigue, sleep, and muscle pain, but people with ME/CFS had more severe cognitive difficulties like trouble concentrating and processing information. Interestingly, loss of smell that lasted a long time in COVID-19 patients appeared connected to their cognitive problems.
Why It Matters
This study provides evidence that ME/CFS and post-COVID-19 condition may share similar underlying pathophysiology despite different triggers, which could inform treatment strategies and research priorities. Understanding the cognitive patterns specific to each condition helps validate brain fog as a measurable symptom rather than psychological, potentially improving clinical recognition and patient support. The potential link between olfactory dysfunction and cognitive decline offers a new avenue for understanding post-viral neurological sequelae.
Observed Findings
Sustained attention was impaired in 83.3% of ME/CFS patients versus 56.2% of post-COVID-19 patients.
Processing speed impairment affected 52.4% of ME/CFS patients versus 41.4% of post-COVID-19 patients.
Both groups showed excessive physical fatigue, sleep problems, and myalgia as primary features.
In post-COVID-19 patients, physical problems and mood issues were the main correlates of cognitive performance; in ME/CFS, anxiety symptoms and physical fatigue were primary correlates.
Prolonged hyposmia (loss of smell) in post-COVID-19 patients appeared associated with cognitive deterioration.
Inferred Conclusions
ME/CFS and post-COVID-19 condition may represent the same underlying pathology triggered by different precipitating factors, given their similar symptom profiles and cognitive impairment patterns.
ME/CFS produces greater severity of both physical and neuropsychiatric symptoms compared to post-COVID-19 condition.
Prolonged loss of smell may serve as a useful marker for identifying cognitive deterioration risk in post-COVID-19 patients.
Cognitive impairment in these syndromes is associated with distinct but overlapping factors, suggesting potentially different therapeutic targets.
Remaining Questions
What This Study Does Not Prove
This cross-sectional study does not establish causation or whether these conditions share an identical underlying mechanism—it only shows similarities in symptom patterns and cognitive impairment. The study cannot prove that loss of smell causes cognitive decline in COVID-19 patients; it only demonstrates correlation. The findings also cannot be generalized to all ME/CFS or post-COVID-19 patients, as this represents a specific sample at one time point.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
What is the underlying biological mechanism that causes similar cognitive impairment patterns in both ME/CFS and post-COVID-19 condition?
Why does ME/CFS show consistently greater cognitive and physical impairment severity compared to post-COVID-19, and what accounts for this difference?
Does olfactory dysfunction reflect broader neurological damage, and can smell loss progression predict worsening cognitive outcomes in post-COVID-19 patients?
Are there specific biomarkers or neuroimaging findings that could distinguish or unify these two conditions?