The experience of post-exertional malaise – part 1

Post-exertional malaise (PEM), the cardinal feature of ME/CFS, is profoundly debilitating and often unpredictable, significantly impacting the lives of those affected.

Existing definitions of PEM, such as in the NICE 2021 guideline, primarily focus on the worsening of symptoms within a specified timeframe following minimal physical or mental exertion, lasting for days, weeks or longer. However, these clinical definitions lack the depth required to truly grasp the nuanced experiences of individuals living with PEM.

Quantitative research, which involves the analysis of numerical data, can provide useful information about the underlying mechanisms of PEM. Cardiopulmonary exercise testing (CPET) has been the main method used to study PEM, and has found physiological differences – such as elevated lactate and differences in brain activity – in people with ME/CFS in comparison with healthy controls.

Yet, whilst quantitative research such as this is crucial in advancing our understanding of ME/CFS, it does not fully capture a person’s experience of PEM, which is particularly relevant in the context of CPET due to the intensity of exertion. The value of qualitative research (involving exploration of subjective experiences) should therefore not be overlooked.

In 2020, Barbara Stussman and colleagues explored the experiences of PEM in 43 people who reported having ME/CFS. Not only did this study provide rich descriptions of what it is like to experience PEM from an individual perspective, it also facilitated a valuable comparison between day-to-day PEM and PEM following CPET.

Beyond contributing to general awareness, the insights gleaned from this study hold relevance for clinicians aiming to comprehend the nuances of PEM and the impact on the daily lives of their patients. Furthermore, researchers conducting investigations involving CPET must consider the potential effects on participants with ME/CFS.

What did the study do?

The study aimed to explore the impact of exertion on individuals with ME/CFS in their daily lives, in contrast to the impact following CPET. The primary focus was on gaining a deeper understanding of PEM by exploring aspects such as the types of symptoms experienced, onset patterns, timeframes for onset, symptom peak, and duration. Drawing on insights from prior literature, the researchers anticipated discovering a sense of loss of control and unpredictability associated with PEM, alongside physical, cognitive and emotional aspects. 

A total of 43 participants were recruited for the study. According to the researchers, “All focus group participants reported having received an ME/CFS diagnosis by a health care provider; an independent verification of medical records was not performed.”

The research involved nine focus groups, each comprising four to seven participants, conducted between November 2016 and August 2019. To specifically investigate PEM following CPET, five of these focus groups were restricted to individuals who had undergone CPET. The focus groups were conducted over the telephone to facilitate geographic diversity without imposing travel burdens on ME/CFS participants, and calls ranged in length from 103 to 120 minutes.

Adopting a grounded theory approach, the researchers systematically gathered and analysed data, allowing themes to emerge organically. This method resembles constructing a theory from the ground up based on what the data reveals, rather than imposing pre-existing theories onto the study. Hence, during the process, focus group scripts (guides with questions to facilitate discussions) were iteratively modified to explore emerging categories.

What did they find?

The study identified eight overarching themes, shedding light on various aspects of PEM:

  1. PEM was triggered by three broad categories of events – physical, cognitive and emotional.
  2. The effects of PEM were impacted by baseline pre-exertional symptoms.
  3. PEM had a wide symptom range with few differences between daily PEM and PEM following CPET, with three core symptoms – exhaustion, cognitive difficulties and neuromuscular complaints.
  4. PEM following CPET was more immediate and of longer duration than PEM in daily life.
  5. The manner of onset of PEM symptoms varied.
  6. Complete rest was necessary to gain any relief in PEM symptoms.
  7. Planning and moderation of energy expenditure were seen as essential to avoiding PEM.
  8. The uncertainty and debility of PEM created despair.

The study provided in-depth exploration and elaboration on each theme, incorporating participant quotes to convey the richness of their experiences.

Read more about this study in part 2 of this article.

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