“Individuals with ME/CFS, particularly those with long COVID, are especially prone to memory and concentration difficulties” finds a study looking at data from the the National Health Interview Survey (NHIS) in the US.
Also known as ‘brain fog‘, cognitive difficulties are common and life-limiting for people with ME/CFS. In the 2021 NICE guideline, cognitive difficulties include “problems finding words or numbers, difficulty in speaking, slowed responsiveness, short-term memory problems, and difficulty concentrating or multitasking”.
Methods
The research team used self-reported data from the NHIS including 27,512 adults who took part in 2022 and 29,404 adults in 2023.
Using information provided in survey responses, four groups were created:
- Long COVID – This group was divided into:
- “Long COVID” which included those who were “currently experiencing new-onset symptoms for three or more months following a COVID-19 infection”
- “No history” which included those with “no current symptoms for three or more months following a COVID-19 infection, or no history of long COVID“.
- ME/CFS – This group included:
- “Current ME/CFS” which referred to those who had ever been told by a doctor or other health professional that they had ‘CFS or ME’
- “No current ME/CFS” which was those who had never been told by a doctor or health professional that they had ‘CFS or “ME’.
- Both: This group referred to those who were in the categories “long COVID” and “Current ME/CFS”
- Neither long COVID nor ME/CFS: This group included those who were in the categories “No history” for long COVID and “No current ME/CFS”.
Data relating to cognitive difficulties, including difficulty remembering and difficulty concentrating, was compared across the groups.
Results
Results showed that in 2022, 3.2% and 1.4% of the population were in the “long COVID” and “current ME/CFS” groups, respectively. This was slightly different in 2023, with figures indicating 3.4% for long COVID, and 0.9% for ME/CFS.
The proportions of those experiencing difficulty remembering and concentrating in each group were:
| 2022 | 2023 | |
| Long COVID | 57.4% | 64.8% |
| ME/CFS | 71.7% | 68.0% |
| Both | 81.1% | 68.7% |
| Neither | 49.3% | 52.0% |
The researchers reported that the findings from their more complex analysis indicate that those with ME/CFS were 5.33 to 6.18 times more likely to experience cognitive difficulty compared to those ‘without ME/CFS’, and that those with long COVID were 2.01 to 2.16 times more likely to experience cognitive difficulty compared to those ‘without long COVID’.
Limitations
In their analysis the researchers state that they controlled for ‘shared variance’ between ME/CFS and long COVID. This means that the analysis aimed to estimate the likelihood of cognitive difficulties in each illness group taking into consideration that the two diagnostic labels are not mutually exclusive. While this is an important complexity to consider, ME Research UK notes that it would have been beneficial for the research team to also carry out analyses looking at cognitive difficulties in each illness group they defined; ME/CFS, long COVID, and both illnesses, in comparison to those who had neither.
A further limitation of this study is that the information used was reported by the participants. All studies using self-reported data are subject to ‘self report bias’ which is the tendency of respondents to answer questions based on social desirability (for example, to under report alcohol consumption). Additionally, the information provided in the survey data used, did not allow researchers to assess the proportion of those who reported a diagnosis of ME/CFS that would meet more stringent ME/CFS diagnostic criteria. Even when extracted from medical notes, research has found that 26% of those who have a diagnosis of G93.3 for “post-viral fatigue”, which includes “benign myalgic encephalomyelitis”, did not meet the Canadian Consensus Criteria (CCC) for ME/CFS.
Additionally, while those with ME/CFS reported whether or not they had ever received a diagnosis from a health professional, those in the long COVID group were those who reported experiencing symptoms of the illness following a COVID-19 infection. This means that while those without a diagnosis of long COVID may have been included, those with symptoms of ME/CFS who did not have a diagnosis of the disease were not. Notably, ME/CFS is often mis-or underdiagnosed, especially in underserved groups, meaning that this method may have missed some people who have the disease, but not a diagnosis.
Conclusions
The findings from this study do indicate increased cognitive difficulties in those with ME/CFS, and in those with long COVID, with highest rates in the group who have both ME/CFS and long COVID. However, the extent to which the results can be interpreted is limited by the analysis method used, and the information available to the research team in the NHIS data.
Importantly, findings from this study relating to ME/CFS add to those published by another team of researchers in the US who used data from the Multi-site clinical assessment of ME/CFS study, and concluded:
“Our findings add to the growing realisation that persons with ME/CFS are compromised cognitively, they are reacting slower, attention is variable over time, and cognitive efficiency supporting executive function, learning and memory is significantly decreased to a clinically meaningful degree.”
When considering studies looking at groups of people with ME/CFS and those with long COVID, it is important to remember that ME/CFS is a symptom-based clinical diagnosis not a mechanistic one. It is clear there is a high degree of shared pathophysiology between ME/CFS and long COVID, and the two diagnostic labels are not mutually exclusive.
