The Frequency of Post-Exertional Malaise (PEM)
Post-Exertional Malaise, or PEM, is the pathological and often delayed worsening of symptoms following minimal physical, cognitive, or emotional exertion. It is considered a hallmark diagnostic feature of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and is also a common symptom of Long COVID.
Frequency of PEM in ME/CFS
For individuals with ME/CFS, the frequency of PEM is remarkably high and is a fundamental component of the illness. Research and clinical reports indicate that it is present in nearly all patients with ME/CFS. For example, a 2018 survey found that over 90% of individuals diagnosed with ME/CFS experienced episodes consistent with PEM. Its presence is so characteristic that it is used to distinguish ME/CFS from other fatiguing illnesses. Patients with ME/CFS are significantly more likely to experience PEM than those with other conditions like major depressive disorder or even multiple sclerosis.
Frequency of PEM in Long COVID
Following the COVID-19 pandemic, PEM became a recognized symptom of Post-acute COVID-19 Syndrome (PACS), commonly known as Long COVID. Its frequency within the Long COVID population has been a key area of study:
- Pooled Prevalence: A 2024 meta-analysis revealed a pooled prevalence of 55% for PEM among PACS patients at least three months after COVID-19 diagnosis.
- Variability in Studies: Other studies have shown a wide range of PEM frequencies in Long COVID patients. A 2023 study found that 98.75% of participants at the Bateman Horne Center reported PEM, whereas a national data analysis in Mexico found an 18.95% rate. This variability often depends on the study's population (e.g., hospitalized vs. non-hospitalized) and the methodology used to assess symptoms.
- Hospitalization and Severity: A study published in The Lancet reported that 36% of patients hospitalized for COVID-19 experienced PEM three years later, suggesting it is a significant long-term consequence.
The Prevalence of Protein-Energy Malnutrition (PEM)
Protein-Energy Malnutrition is a serious form of undernutrition caused by insufficient intake or absorption of protein and calories. It is a major health burden globally, particularly affecting children and the elderly.
PEM in Children
In developing countries, PEM in children under five is a widespread problem. A 2018 study in rural Lahore, Pakistan, found that 52.8% of children suffered from PEM, identifying socioeconomic status, parental literacy, and dietary habits as significant contributing factors. Another study in the same region, published in 2023, reported a 4.22% incidence rate of severe PEM in children under five, highlighting the ongoing issue. Globally, PEM accounts for a significant number of deaths annually, predominantly impacting vulnerable children in low-income regions.
PEM in Older Adults
In industrialized nations, PEM is often seen in clinical settings, particularly among institutionalized older adults. Studies on residential care facilities report a high prevalence of undernutrition (which includes PEM), with rates ranging from 12% to 54%. The risk of PEM in this population is influenced by factors like chronic disease, decreased appetite, and cognitive issues such as dementia.
Comparison of PEM Frequencies
| Condition | Frequency | Context | Typical Triggers | Measurement Methods |
|---|---|---|---|---|
| Post-Exertional Malaise (PEM) | Very high in ME/CFS (90%+). Variable in Long COVID (e.g., 55% pooled prevalence). | Chronic neuroimmune illness, often post-viral. | Physical, cognitive, emotional, sensory exertion. | Validated patient questionnaires (e.g., DSQ-PEM), two-day cardiopulmonary exercise tests (CPET). |
| Protein-Energy Malnutrition (PEM) | High in vulnerable populations (e.g., 52.8% in some rural child populations). Common in institutionalized elderly. | Global malnutrition crisis, chronic illness, older adults. | Insufficient food intake, poor diet, underlying disease, impaired absorption. | Anthropometric measures (weight, height, BMI, MUAC), blood tests (albumin, transferrin), and dietary history. |
Factors Influencing the Frequency of PEM
For Post-Exertional Malaise, the frequency within a susceptible population is influenced by factors such as the severity of the underlying illness and individual energy envelopes. A person's tolerance for exertion can fluctuate, making PEM episodes unpredictable and varying in intensity. Overexertion, even slight, is the main driver. In contrast, the frequency of Protein-Energy Malnutrition is influenced primarily by socioeconomic conditions, access to proper nutrition, age, and co-morbidities. In clinical settings, factors like impaired nutrient absorption from disease also play a role.
Conclusion: Interpreting the Frequency of PEM
The term 'PEM' requires context to be understood correctly. While the abbreviation is identical, the conditions are entirely separate in their causes, affected populations, and diagnostic criteria. The frequency of Post-Exertional Malaise is extremely high among those with ME/CFS and is a significant symptom for over half of Long COVID patients, confirming it as a central feature of these complex neuroimmune diseases. Meanwhile, the prevalence of Protein-Energy Malnutrition remains a serious and widespread global health issue, disproportionately affecting children in poverty and institutionalized older adults. Understanding this distinction is crucial for both diagnosis and management of these two different conditions. To better understand the nature of PEM as it relates to ME/CFS and Long COVID, see the educational resources from ME/CFS Australia.
