MEA Summary Review: Assessing PEM – The characteristic symptom of ME/CFS | 25 March 2019

March 25, 2019


Charlotte Stephens, Research Correspondent, ME Association.


Post-exertional malaise (commonly referred to as PEM) is considered a hallmark characteristic of ME/CFS. However, it is not a requirement in many of the different diagnostic criteria.

There is currently no agreed upon definition of PEM, nor a formal assessment for its measurement, but creating one could improve future diagnosis of the disease.

Dr Melvin Ramsay – the clinical champion of M.E. and founding member of the ME Association – originally described what has since become known as PEM, as:

“Muscle fatigability whereby, even after a minor degree of physical effort, three, four, or five days, or longer, elapse before full muscle power is restored and constitutes the sheet anchor of diagnosis.”

“Without it I would be unwilling to diagnosis a patient as suffering from ME, but it is most important the stress the fact that cases of ME of mild or even moderate severity may have normal muscle power in remission.”

The Saga of the Royal Free Disease (50th Anniversary Reprint).

Since then the definition of PEM has expanded, but no single version or means of assessment has really prevailed (see References for recent research on this topic).

However, in recent years we have witnessed the development of objective evidence that supports PEM as a real and unique symptom.

Latest Research

Earlier this month Professor Lenny Jason and his team from the Center for Community Research at DePaul University in Chicago, published results of a large public survey on PEM.

They hope the analysis will lead to a definitive definition and will ultimately provide a validated clinical assessment tool.

In this review, we hope to explain what PEM is, cover some of the research surrounding it and give an overview of the results from this latest research.

Image credit: 123RF/Wavebreak Media Ltd.

Click here to download and read the complete research summary

Please visit our Research section for a complete listing of all the Summaries we have available.

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