Post-Exertional Malaise
Post-Exertional Malaise (PEM) is a cardinal symptom of ME/CFS. By definition, post-exertional malaise is an exacerbation of ME/CFS symptoms occurring after physical or mental activity that was previously tolerated. These symptoms may appear immediately after the activity or after a delay, and they may last for days to weeks or more.
The symptoms of post-exertional malaise were discussed by Lily Chu (Stanford University). In a study of 144 PWCs she found that:
- post-exertional malaise symptoms include fatigue, cognitive difficulties, sleep disturbance, headache, muscle pain and flu-like symptoms
- more than 90% experience post-exertional malaise, and 10% experience emotional distress after exertion as well
- the onset of PEM is variable in 40% of PWCs, and occurs more than 24 hours after exertion in 15%
- post-exertional malaise lasts more than 3 days in 25% of PWCs
- 10% of subjects reported that PEM lasted 24 hours or less, with 90% reporting much longer
- physical and cognitive exertion trigger PEM more than emotional distress
PEM can be demonstrated objectively by obtaining cardio-pulmonary exercise testing (CPET) on two consecutive days. Healthy controls produce the same results on both tests; but PWCs perform less well the second day due to this post-exertional malaise. This was elegantly presented to us by Staci Stevens, Drs. Snell and VanNess, and Dr. Keller at the 2014 IACFS conference in San Francisco.
This year Dr. Keller presented subsets of patient responses to the 2-day CPET. In most PWCs, VO2 max (aerobic work capacity) falls by 7% or more the second day and the VO2@VAT (aerobic capacity at the Anaerobic Threshold) decreases by 12% or more. In a subset of patients with autonomic anomalies, however, the heart rate may fail to rise significantly or the systolic blood pressure fails to rise more than 10mmHg/MET. Another subset presents with ventilatory anomalies (e.g., failure to increase respiratory rate appropriately). In her pool of 97 patients who underwent 2-day CPETs:
- 34% failed to reproduce the VO2 peak
- 39% failed to reproduce the VO2 @VAT peak
- 43% demonstrated autonomic anomalies
- 47% demonstrated ventilatory anomalies, and
- 29% had normal responses on testing.
This latter group can generally exercise without experiencing significant post-exertional malaise. About 10% of them, however, still demonstrate autonomic or ventilatory anomalies.
Keller also reported that levels of CRP (C-Reactive Protein) tend to be higher in PWCs than controls, and increase with the second CPET./QUOTE]
