A recently published research article in ‘Trends in Neurosciences' reviews the presentation, possible causation and treatment of cognitive dysfunction/brain fog in a number of medical conditions, including ME/CFS and Long Covid.
Denno, Zhao, Husain, and Hampshire (2025)
Summary
- Symptoms: Brain fog commonly involves cognitive dysfunction, like difficulty with focus, memory lapses, and slowed thinking, often combined with fatigue, anxiety, and mood disturbances.
- Causes: The paper suggests that brain fog results from both cognitive performance issues and noncognitive factors like fatigue and emotional stress, with different medical conditions showing varying contributions of these elements.
- Post-COVID-19 Brain Fog: Long Covid is used as a case study, highlighting how brain fog persists as a long-term symptom, often affecting memory, attention, and executive function.
- Neural Correlates: The paper discusses previous research on brain imaging and biomarkers which showed some structural brain changes and inflammation markers, but no consistent neurobiological cause has been pinpointed across conditions.
- Research Challenges: It calls for clearer definitions and standardised measures to study brain fog, arguing that the term itself may be too broad and imprecise. Future research should aim to distinguish different elements of brain fog and explore possible shared mechanisms.
Extracts
Abstract
‘Brain fog' is commonly reported in more than a dozen chronic diseases, but what is it? We review research across conditions which has characterised brain fog and evaluate its definitions and objective correlates. Brain fog has been used to refer to a variable set of overlapping symptoms implicating cognition, fatigue, and affect. It has been defined as a distinct symptom, a syndrome, or a nonspecific term.
We consider the evidence that brain fog is a transdiagnostic entity with a common phenomenology and profile of objective cognitive deficits. We discuss where these commonalities arise and argue that linguistic ambiguity, shared cognitive impairments, and noncognitive factors are more likely than shared neurobiology. We suggest how future research might apply existing tools to disambiguate the phenomena that brain fog conflates.
“Although there is evidence that a wide range of mechanisms are associated with brain fog, few are shared, and many appear to be
Denno et al
disorder-specific. While there may be shared mechanistic factors further down the causal chain, such as neuroinflammation, BBB dysfunction, or impaired cerebral perfusion homeostasis and current evidence for these is limited to specific conditions.”
MEA Comment
“Cognitive dysfunction, also known as ‘brain fog' , refers to problems with short term memory, concentration, information processing and word finding abilities. It is a common and disabling symptom in both ME/CFS and Long Covid.
This is a detailed review of the presentation, possible causation and treatment of cognitive dysfunction/brain fog in a number of medical conditions where this can be an important and disabling feature.
The MEA has an information leaflet covering the management of cognitive dysfunction in ME/CFS.”
Dr Charles Shepherd,
Trustee and Hon. Medical Adviser to the ME Association,
Member of the 2018-2021 NICE guideline on ME/CFS committee,
Member of the 2002 Chief Medical Officer's Working Group on ME/CFS
