Many people with ME/CFS would consider that their most significant problem is post-exertional malaise (PEM) – that worsening of symptoms that follows even minimal physical (and sometimes mental) effort.

Although PEM is included in existing case definitions for ME and CFS – such as the Fukuda and Canadian Consensus Criteria – these documents often do not agree on how it is defined, or whether it is even required for diagnosis.

Furthermore, there appear to be considerable differences among patients in the specific symptoms they experience, and also in what kind of activities or other factors trigger their exacerbations.

In 2018, the National Institutes of Health/Center for Disease Control and Prevention (NIH/CDC) convened a working group to develop a new definition of PEM. While this may be a useful step, it has been criticised by the patient community, and a new paper from Prof. Leonard Jason’s group at DePaul University, Chicago, suggests that the “types of general descriptions [arrived at by the working group] need to be operationalized if investigators are to reliably use them to assess PEM”.

Prof. Jason’s paper was published recently in the journal Diagnostics (freely available online), in which the authors describe their attempts – in collaboration with the patient community – to develop a valid, comprehensive tool to assess PEM.

They revised the NIH/CDC descriptions into a usable questionnaire, which was shared with patient groups, and subsequently revised several times in response to the many comments received. The final questionnaire was then completed, more formally, online by 1,534 patients with ME or CFS.

The study concluded that there are several aspects of PEM that are particularly critical, some of which have not been assessed in previous tools.

These include the timing of onset, the triggers of PEM, which symptoms are exacerbated, how the consequences are described, the duration of PEM, the length of recovery, and the importance of other characteristics such as duration and course of illness, level of functioning, and coping methods used.

A total of 87.5% of participants felt that the survey accurately or very accurately captured their experiences of PEM.