Fatigue in illnesses like ME/CFS has been found to be multifaceted, multidimensional, and far removed from the everyday ‘tiredness’ experienced by healthy people.
An ME Research UK-funded study compared fatigue across 5 chronic disease groups, including ME/CFS. Results showed that the nature of fatigue was similar across all 5 groups, suggesting that symptoms like fatigue arise due to generic disease processes that chronic illnesses share. Despite this, people with ME/CFS had much higher levels of total fatigue than any of the other group.
While researchers are making progress with studies relating to fatigue, it is essential to recognise that they face many challenges, including, but not limited to
- Lack of validated biomarker and reliance on self-reported information.
- Fatigue is subjective and highly complex, and varies between individuals.
The following will discuss the above research difficulties in more detail, and provide ME Research UK resources relevant to research into brain fog in ME/CFS.
Research challenges
Lack of validated biomarker and reliance on self-reported information.
As with ME/CFS overall, there is no validated biomarker for fatigue. Rather, the symptom is often measured using self-reported information. While these measures do provide insight into self-reported fatigue levels, they are subjective, which means that the questions could be interpreted differently by different participants. While some studies do look more closely at fatigue by looking at things like reaction time, blink rate, heart rate variability, or muscle strength testing, none of these are specific to fatigue in ME/CFS.
Fatigue is subjective and highly complex, and varies between individuals.
Fatigue is not a one-size-fits-all experience; it is deeply subjective and shaped by a complex interplay of physical, psychological, and environmental factors. Importantly, what feels like mild fatigue to one person may be overwhelming to another. Because of this variability and subjectivity, fatigue in ME/CFS is difficult to capture accurately in research, and different studies often use different methods to assess it, meaning that results may not be comparable.
Resources
1. ME Research UK articles relating to fatigue:
- Perceived fatigue is comparable between different disease groups
- The Newcastle NHS Chronic Fatigue Syndrome Service: not all fatigue is the same
- Fatigue severity remains stable over time and independently associated with orthostatic symptoms in chronic fatigue syndrome: a longitudinal study
2. Completed research funded by ME Research UK relating to diagnosis and symptoms.
3. Ongoing research funded by ME Research UK looking at cause-effect relationships in the mitochondrial energy inefficiency in ME/CFS – Dr Sarah Annesley & Tina Katsaros
