There are a number of possible definitions of ME and CFS but each is different, and the terms ME, CFS and their various combinations mean different things to different people today. Many different views and opinions exist about which definition might be ‘best’, but hard data is thin on the ground. Fortunately, there are ongoing attempts to compare definitions, and the latest comes from Prof Leonard Jason’s very active research group at DePaul University, Chicago which has compared the most widely used CFS criteria (Fukuda 1994) with the relatively new International Consensus Criteria for ME (ME-ICC 2011)

The Chicago group’s main finding is that people who meet both Fukuda and ME-ICC criteria have poorer function (lower physical function, more physical pain, etc) and more severe symptoms than those meeting Fukuda criteria alone. This is no real surprise, since it is probably easier for patients with milder symptoms or lower levels of disability to meet the Fukuda criteria than to meet the ME-ICC criteria which are more stringent. The surprising thing is that levels of psychiatric illness seem to be higher in the ME-ICC group; as the authors say, “while the ME-ICC criteria are an improvement over the vague and minimal guidelines of Fukuda it is possible that the ME-ICC criteria select for individuals with increased psychiatric symptoms and functional impairment.”

This is a preliminary report, and its results may be overturned in subsequent investigations. However, it illustrates that we cannot just assume that this or that definition is ‘better’ than another; each will have its strengths and weaknesses, and only experimentation can draw these out.

Reference: Contrasting Case Definitions: The ME International Consensus Criteria vs. the Fukuda CFS Criteria. Brown et al. North American Journal of Psychology, March 2013