Post-exertional malaise (PEM), often referred to as the cardinal symptom of ME/CFS, is defined by the 2021 NICE guideline for the diagnosis and management of the disease, as:
“The worsening of symptoms that can follow minimal cognitive, physical, emotional or social activity, or activity that could previously be tolerated. Symptoms can typically worsen 12 to 48 hours after activity and last for days or even weeks, sometimes leading to a relapse. Post-exertional malaise may also be referred to as post-exertional symptom exacerbation.”
It has been observed that existing definitions of PEM may not fully capture the experience of individuals living with ME/CFS. It is also clear that PEM is a complex symptom that not only differs between individuals, but can fluctuate in duration and severity within the same individual over time.
The complexity of the PEM – and the inconsistencies in both type, and level of, activity that trigger it – makes it very hard for individuals to gauge overexertion and manage their symptoms, and for researchers to accurately capture it.
To try and obtain a better understanding, a group of researchers – including Professor Leonard Jason – considered whether there might be distinct subtypes of PEM.
The team looked at information – collected prior to the COVID-19 pandemic – on 2,068 participants who had all completed the Depaul Symptom Questionnaire (DSQ).
Within the DSQ is a specific section relating to various aspects of participants experiences of PEM (DSQ-PEM). Here, participants rated the frequency and severity of each of the following items on a five-point scale.
- “Dead, heavy feeling after starting to exercise,”
- “Next day soreness or fatigue after non-strenuous, everyday activities,”
- “Mentally tired after the slightest effort,”
- “Minimum exercise makes you physically tired,”
- “Physically drained or sick after mild activity.”
From these, item 3: “Mentally tired after the slightest effort,” and item 4: “Minimum exercise makes you physically tired,” were chosen to represent the mental and physical manifestations of PEM.
Based on self-reported symptom frequency and severity, participants with ME/CFS were grouped based on the type of PEM they experienced:
- Both physical and mental: The 1,535 people with a score of more than 2 for frequency and severity in both items.
- Physical only: The 264 people who scored more than 2 for frequency and severity in the item representing the physical manifestations of PEM, but less than 2 for frequency and severity in the item representing the mental manifestations of PEM.
- Mental only: The 89 people who scored more than 2 for frequency and severity in the item representing the mental manifestations of PEM, but less than 2 for frequency and severity in the item representing the physical manifestations of PEM.
- Neither: The 78 people who scored less than 2 for frequency and severity in the items representing both the physical and mental manifestations of PEM.
It is worth noting that the participants in the ‘neither’ group still reported symptoms of PEM. However, the frequency and severity of PEM experienced was below the threshold values used in this study. Additionally, 102 participants without ME/CFS were included in the analysis as a control group.
When only considering those with ME/CFS, participants in the ‘Both’ group had the greatest symptom burden across all PEM items in the DSQ, and those in the the ‘Neither’ group the lowest. Despite this, those in the ‘neither’ group still had a significantly higher symptom burden when compared with controls.
Limitations of the study, acknowledged by the authors, included that those in the control group were significantly younger than with ME/CFS, and a lack of diversity amongst participants as the population was predominantly white.
Future research recommendations made in the paper related to the need for more diverse sample populations, and studies that follow participants up over time (longitudinal studies). It is also noted that studies investigating potential treatments should consider effectiveness by PEM subtype with the researchers concluding:
“Given the differences in symptom experiences, patients may better benefit from treatments tailored specifically to alleviate different aspects of their PEM symptoms.”
ME Research UK adds that the findings from this project likely contribute to ME/CFS disease heterogeneity, and have implications for research. As such, it is important that when investigating PEM, researchers consider that there may be different subtypes, and that PEM can be triggered not only by physical activity, but also by cognitive and emotional exertion.
