From 1994 and on, I have been doing research that shows some of the diagnostic problems with the Fukuda case definition. And remember, the Fukuda case definition is the research case definition that has been used throughout the world for the past 25 years. But this Fukuda case definition identifies a heterogenous group of patients, because core symptoms are not required of all patients. So, as a consequence, samples of patients with CFS based on Fukuda case definition vary widely in different research groups and labs. What is the impact of the case definitions on prevalence rates? In the late 1980s and early 1990s, the CDC conducted a prevalence study where they started by asking physicians in four cities to identify patients they thought had CFS. At that time, a lot of physicians didn’t believe CFS existed, so putting physicians as gatekeepers in the selection of patients for this study resulted in a prevalence rate that was very low. Also, many people in the US do not have the financial resources to have a physician, so relying on primary care doctors to identify patients was another reason for low prevalence rates. The study suggested that CFS was a rare disease that affected fewer than 20,000 people in the US. At that point, a group of researchers in Chicago began working on a study that involved finding patients from a random community sample, rather than a sample referred from physicians. In 1995, with NIH funding, our Chicago research team conducted a community-based prevalence study, which found that about a million people in the US had CFS. We also found that CFS affected all ethnic and socioeconomic groups, and thus we helped shatter the myth that CFS was a “Yuppie Flu” disease. What did William Reeves [then-head of the CDC division in charge of the illness] do with the so-called “empiric” criteria? And why did this increase the CDC’s estimate of disease prevalence by a factor of 10? In the early 2000s, Bill Reeves felt there was a need to operationalize the Fukuda case definition. For example, he tried to standardize the way we measure a patient’s disability or a substantial reduction in functioning. He used one instrument that has been referred to as the SF-36. According to Reeves, if a patient met criteria for one of several sub-scales within the SF-36, the patient would meet the disability criteria for having CFS. But one of these domains was “role emotional” functioning. It turns out that every person with a major depressive disorder meets the criteria for “role Page 42 of 56 www.investinme.org emotional” functioning. So you can’t just specify instruments such as the SF-36; you have to specify which sub-scales of the instruments you are going to use, and what are the cut-off points. And if any of these choices are wrong, you will identify people who have another illness. My team gathered data on this point, and we conducted a study that assessed people with major depressive disorder, and found that over onethird of them could be inappropriately classified as having CFS under the so-called Reeves empiric criteria. So, I think in the attempt to operationalize the Fukuda criteria, Reeves made mistakes, and I believe that is one of the reasons the estimated CDC prevalence estimates increased ten-fold, from .24% in a 2003 sample to 2.54% in 2007. They operationalized the Fukuda criteria in a way that classified many people as having CFS when they really had other illnesses. At that time, many thought this increase in prevalence figures that Reeves proposed was constructive as it suggested that far more people had the illness, and thus these findings could be used to argue for more attention and funding due to this illness being so widespread. But if you use a very broad criteria, and bring into the illness case definition people who don’t have the disease, then the entire research effort is seriously compromised. Fortunately, over the past decade, few researchers have used the Reeves way of operationalizing CFS. What about the CCC and ICC criteria? The CCC case definition for ME/CFS in 2003 was better because it specified key symptoms such as PEM. It was developed as a clinical case definition, and now it’s being used by several teams as a research case definition. With the 2011 ME-ICC, I have noticed problems, and in part this is due to them once again requiring too many symptoms that could, as with the Holmes criteria of 1988, bring into the ME category some individuals who have a primary psychiatric disorder. In addition, the ME-ICC criteria is complicated to use, and many clinicians and scientists will have a difficult time reliably using it with patients. What is the problem you see with the IOM case definition, apart from the name? Well, it is true that Systemic Exertion Intolerance Disease (SEID) is a name most patients dislike. However, the IOM report was correct in requiring several core symptoms, such as PEM. But I believe these authors made a mistake in indicating that a patient could have either cognitive impairment or orthostatic intolerance— Invest in ME research (Charity Nr. 1153730)

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