Differences in ME and CFS symptomology in patients with normal and abnormal exercise test results, by Stephanie L McManimen and Leonard A Jason in International Journal of Neurology and Neurotherapy 2017, vol 4 issue 1, 4:066 [Published: March 21, 2017]
Post-exertional malaise (PEM) is a cardinal symptom of myalgic encephalomyelitis (ME) and chronic fatigue syndrome (CFS), which often distinguishes patients with this illness from healthy controls or individuals with exclusionary illnesses such as depression. However, occurrence rates for PEM fluctuate from subject to how the symptom is operationalized. One commonly utilized method is exercise testing, maximal or submaximal. Many patients with ME and CFS experience PEM after participating in these tests, and often show abnormal results.
However, some patients still exhibit normal results after participating in the exercise testing. This study examined the differences between two patient groups with ME and CFS, those with normal results and those with abnormal results, on several PEM-related symptoms and illness characteristics. The results suggest those that displayed abnormal results following testing have more frequent and severe PEM, worse overall functioning, and are more likely to be bedbound than those that displayed normal results.
Excerpt from research article:
These findings suggest there is a subgroup of patients with ME and CFS that is more functionally impaired than the rest of the patient population. Although both groups of
participants endorsed PEM-related symptoms, the group with the abnormal results displayed higher frequency and severity for the symptoms. Since this group appears to
be more impaired, they may have a lower threshold for exertion, which could result in them experiencing PEM more quickly than the group with normal test results.
Conversely, the group with normal test results may require more exertion before the results would differ from those of healthy controls as they are not as functionally impaired
as the group with abnormal test results.
This finding result in a heterogeneous patient population for research involving exercise testing, which may help explain the discrepant results found in previous studies.
Additionally, since the group with abnormal exercise test results is more likely to be bedbound or housebound, it is possible that they are unable to make it to a tertiary
clinic to participate in these research studies. As a result, the more severely impaired group patients with ME and CFS may be excluded from analyses comparing the full patient population to healthy control populations. This could prevent researchers from finding significant differences between patients and controls if the more impaired patients
are unable to participate in research.
This study has several limitations. First, this study used an international convenience sample. All participants had a self-reported, current diagnosis of ME or CFS so there was no standardized diagnostic criteria necessary to participate in this study. The study also included participants from many settings and countries. Previous research has shown differences in patient populations between US and UK samples.
However, this may actually be seen as an advantage as it would allow for us to generalize the results across various settings (i.e. tertiary care, community, and primary care samples) and geographic locations.
Additionally, we do not have information on the types of tests that were performed, submaximal or maximal. The participants self-reported that they had previously
received normal or abnormal exercise test results. Future research should examine the functional and symptomatic differences between the patients with normal and abnormal
results in a controlled, standardized study to form a more homogenous patient sample.