What is known about brain fog and cognitive difficulties in POTS, ME/CFS, fibromyalgia and long COVID?
Attention, memory and processing-speed difficulties: what studies show, without reducing brain fog to a single diagnosis.
- 10 sources
- 5 min read
- Clinical review
- Verified 9 November 2026
Key points
- “Brain fog” is an expression used to describe difficulties with concentration, memory, finding words or slowed responses; the sources consulted use it to describe symptoms, not as the name of a disease [1, 2].
- In POTS, a case-control study comparing 28 women with 24 controls observed lower scores in selective attention, processing speed and executive function, but not in all the cognitive domains tested [3].
- A 2022 ME/CFS meta-analysis found differences in immediate visuospatial memory, reading speed and episodic memory, while highlighting the heterogeneity of the cognitive profile [4].
- A 2026 meta-analysis of working memory in ME/CFS (34 studies) found a large difference for verbal working memory, but no significant difference for visual working memory [5].
- Complaints and test results do not always match: in six adolescents with POTS referred for cognitive difficulties, standardized test results were in the average range or above, despite a major impact on schooling [6].
A descriptive expression
POTS: neuropsychological data
ME/CFS: cognitive profiles
Fibromyalgia: “fibro-fog”
Long COVID and other contexts
Interpretation and caution
References and level of evidence
- NICE. Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management (NG206). NICE guideline 2021.(guideline or consensus)Limitations: UK guideline; not a French or US framework. Population: children, young people and adults with suspected or diagnosed ME/CFS. Read: online recommendations.Declared conflicts of interest: Institutional document; committee declarations not consulted
- CDC. Clinical Symptoms of Long COVID. CDC – Long COVID (page updated March 9, 2026) 2026.(expert opinion)Limitations: Clinical page listing commonly reported symptoms; gives no formal definition of long COVID and does not mention post-exertional malaise. Read: official page.Declared conflicts of interest: Institutional document
- Arnold AC, Haman K, Garland EM, Raj V, Dupont WD, Biaggioni I, Robertson D, Raj SR. Cognitive dysfunction in postural tachycardia syndrome. Clinical Science (London), 128(1):39–45 2015. DOI: 10.1042/CS20140251. PMID: 25001527.(observational study)Limitations: Case-control study: 28 women with POTS and 24 age- and sex-matched controls; tests performed in a semi-recumbent position. Read: abstract.Declared conflicts of interest: Not reviewed in the part of the source that was read
- Aoun Sebaiti M, Hainselin M, Gounden Y, Sirbu CA, Sekulic S, Lorusso L, Nacul L, Authier FJ. Systematic review and meta-analysis of cognitive impairment in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Scientific Reports, 12(1):2157 2022. DOI: 10.1038/s41598-021-04764-w. PMID: 35140252.(evidence synthesis)Limitations: Studies published from 1988 to 2019, with patients defined mainly by the 1994 CDC criteria; heterogeneous tests. Read: full text (PMC8828740).Declared conflicts of interest: The authors declare no conflicts of interest; funded by AFM and the COST program
- Penson M, Kelly K. Evaluating working memory functioning in individuals with myalgic encephalomyelitis/chronic fatigue syndrome: a systematic review and meta-analysis. Psychology, Health & Medicine (published online January 8, 2026) 2026. DOI: 10.1080/13548506.2025.2606183. PMID: 41504224.(evidence synthesis)Limitations: 34 studies; full text not read. Read: abstract.Declared conflicts of interest: Not reviewed in the part of the source that was read
- Koch SA, Jarjour IT, Evankovich KD. Neurocognitive Profiles in Adolescents With Postural Tachycardia Syndrome and Perceived Brain Fog: A Preliminary Report. Pediatric Neurology, 148:128–132 2023. DOI: 10.1016/j.pediatrneurol.2023.08.011. PMID: 37703657.(exploratory finding)Limitations: Chart review of six adolescents from a pediatric neurology clinic; no generalization possible. Read: abstract.Declared conflicts of interest: Not reviewed in the part of the source that was read
- Assurance Maladie. Un cas particulier : le syndrome de fatigue chronique ou encéphalomyélite myalgique. ameli.fr (updated August 28, 2026) 2026.(expert opinion)Limitations: General-public information page; it is neither a French National Authority for Health (HAS) guideline nor a French national diagnosis and care protocol (PNDS). Read: official page.Declared conflicts of interest: Institutional document
- Haute Autorité de santé (HAS). Fibromyalgie de l'adulte : conduite diagnostique et stratégie thérapeutique. HAS (French National Authority for Health) good practice guideline (adopted June 19, 2025, published online July 10, 2025) 2025.(guideline or consensus)Limitations: French guideline for adults; does not automatically apply to children or outside France. Read: overview page and the “Recommendations” document (in French).Declared conflicts of interest: Not reviewed in the part of the source that was read
- Wu YL, Huang CJ, Fang SC, Ko LH, Tsai PS. Cognitive Impairment in Fibromyalgia: A Meta-Analysis of Case-Control Studies. Psychosomatic Medicine, 80(5):432–438 2018. DOI: 10.1097/PSY.0000000000000575. PMID: 29528888.(evidence synthesis)Limitations: 23 case-control studies published before September 2017; heterogeneous tests. Read: abstract.Declared conflicts of interest: Not reviewed in the part of the source that was read
- Nicholls T, Kelly K. Assessing working memory function in individuals with fibromyalgia: A systematic review and meta-analysis. Applied Neuropsychology: Adult (published online October 14, 2025) 2025. DOI: 10.1080/23279095.2025.2570780. PMID: 41086106.(evidence synthesis)Limitations: 29 studies; full text not read. Read: abstract.Declared conflicts of interest: Not reviewed in the part of the source that was read