by Mary Dimmock and Jennie Spotila
How do ME and CFS differ? Do these illnesses lie along the same continuum of severity or are they entirely separate with common symptoms? What makes them different, what makes them the same? What is lacking in each case definition – do the non-overlapping elements of each case definition identify a subset of the illness or do they encompass the entirety of the population?
Boiled down to its essence, this set of questions is asking whether all the “ME/CFS” definitions represent the same disease or set of related diseases. The failure to ask this question puts the entire effort at risk.
This fundamental question was posed in the 2012 application for the Office of Disease Prevention to hold the P2P meeting (which I obtained through FOIA). It was posed in the 2013 contract between AHRQ and the Oregon Health & Science University for the systematic evidence review (which I obtained through FOIA). It was posed to the P2P Working Group at its January 2014 meeting to refine the questions for the evidence review and Workshop (according to Dr. Susan Maier at the January 2014 Institute of Medicine meeting).
And then the question disappeared.
The systematic evidence review protocol does not include it. Dr. Beth Collins-Sharp said at the June 2014 CFSAC meeting that the Evidence Practice Center is not considering the question because there is “not enough evidence” in the literature to answer the question. However, she said that the P2P Workshop could still consider the question.
But the draft agenda for the Workshop does not include it. Furthermore, every aspect of the P2P Workshop treats “ME/CFS” as a single disease:
- The P2P description of ME/CFS refers to it as a single disorder or illness throughout the meeting webpage.
- The P2P website characterizes the names myalgic encephalomyelitis and chronic fatigue syndrome as synonymous.
- Every section of the Workshop agenda lumps all the populations described by the multiple case definitions together, discussing prevalence, tools, subsets, outcomes, presentation, and diagnosis of this single entity.
A 20 minute presentation on “Case Definition Perspective” is the only lip service paid to this critical issue. This is completely inadequate, if for no other reason than because the presentation is isolated from discussions on the Workshop Key Questions and dependent topics like prevalence and natural history. As a result, it is unlikely to be thoroughly discussed unless one of the Panelists has a particular interest in it.
Why is this problematic? Because both the P2P Workshop and the evidence review are based on the assumption that the full set of “ME/CFS” case definitions describe the same disease. This assumption has been made without proof that it is correct and in the face of data that indicate otherwise, and therein lies the danger of failing to ask the question.
What if the case definitions do not actually describe a single disease? If there are disparate conditions like depression, deconditioning, non-specific chronic fatigue and a neuroimmune disease characterized by PEM encompassed by the full set of “ME/CFS” definitions, then lumping those together as one entity would be unscientific.
The most important part of designing scientific studies is to properly define the study subjects. One would not combine liver cancer and breast cancer patients into a single cohort to investigate cancer pathogenesis. The combination of those two groups would confound the results; such a study would be meaningful only if the two groups were separately defined and then compared to one another to identify similarities or differences. The same is true of the P2P evidence review of diagnostics and treatments: assuming that all “ME/CFS” definitions capture the same disease (or even a set of biologically related diseases) and attempting to compare studies on the combined patients will yield meaningless and confounded results if those definitions actually encompass disparate diseases.
There is a growing body of evidence that underscores the need to ask the fundamental question of whether “ME/CFS” definitions represent the same disease:
- The P2P Workshop is focused on “extreme fatigue” as the defining characteristic of “ME/CFS,” but fatigue is a common but ill-defined symptom across many diseases. Further, not all “ME/CFS” definitions require fatigue or define it in the same way. For instance, Oxford requires subjective fatigue, and specifically excludes patients with a physiological explanation for their fatigue. But the ME-ICC does not require fatigue; instead it requires PENE, which is defined to have a physiological basis.
- When FDA asked CFS and ME patients to describe their disease, we did not say “fatigue.” Patients told FDA that post-exertional malaise was the most significant symptom: “complete exhaustion, inability to get out of bed to eat, intense physical pain (including muscle soreness), incoherency, blacking out and memory loss, and flu-like symptoms.”
- Multiple studies by Jason, Brenu, Johnston and others have demonstrated significant differences in disease severity, functional impairment, levels of immunological markers and patient-reported symptoms among the different case definitions.
- Multiple studies have demonstrated that patients with PEM have impairment in energy metabolism and lowered anaerobic threshold, and have shown that patients with depression, deconditioning and a number of other chronic illnesses do not have this kind of impairment.
- Multiple studies have demonstrated differences in exercise-induced gene expression between Fukuda/CCC patients and both healthy and disease control groups.
- The wide variance in prevalence estimates shines a light on the case definition problem. Prevalence estimates for Oxford and Empirical populations are roughly six times higher than the most commonly accepted estimate for Fukuda. Even Fukuda prevalence estimates vary widely, from 0.07% to 2.6%, underscoring the non-specificity of the criteria. Nacul, et al., found that the prevalence using CCC was only 58% of the Fukuda prevalence. Vincent, et al., reported that 36% of Fukuda patients had PEM, representing a smaller population that would be eligible for diagnosis under CCC.
- The work of Dr. Jason highlights the danger of definitions that include patients with primary psychiatric illnesses, especially because such patients may respond very differently to treatments like CBT and GET.
By contrast, there have not been any published studies that demonstrate that the set of “ME/CFS” definitions being examined in P2P encompass a single entity or biologically related set of entities. From Oxford to Fukuda to ME-ICC, there are significant differences in the inclusion and exclusion criteria, including differences in the exclusion of primary psychiatric illness. The magnitude of these differences makes the lack of such proof problematic.
Given that treating all “ME/CFS” definitions as a single entity is based on an unproven assumption of the clinical equivalence of these definitions, and given that there is ample proof that these definitions do not represent the same disease or patient population, it is essential that the P2P “ME/CFS” study start by asking this question:
Does the set of “ME/CFS” definitions encompass the same disease, a spectrum of diseases, or separate, discrete conditions and diseases?
The failure to tackle this cornerstone question up-front in both the agenda and the evidence review puts the scientific validity of the entire P2P Workshop at risk. If this question is not explicitly posed, then the non-ME/CFS expert P2P Panel will swallow the assumption of a single disorder without question, if for no other reason than that they do not know the literature well enough to recognize that it is an assumption and not established fact.