Speculative but thought provoking Ellen Goudsmit, NA 2 October 2013 As a former archivist who has read almost all publications on myalgic encephalomyelitis (ME) and chronic fatigue syndrome (CFS), I have come across papers linking MS and CFS before. They've noted similarities but also differences. The problem with ME/CFS, or CFS/ME, is that it has not been formally defined. Some studies referring to CFS/ME select patients using broad criteria for CFS. These overlap about 97% with the criteria for neurasthenia (i.e. if you meet the criteria for one, you will almost certainly meet the criteria for the other). Almost no one still studies ME as described by experts such as Dr Ramsay and others prior to 1988. Indeed, I believe that I was the last one. It's not yet been established that ME is equivalent to CFS, so combining the two leads to the question, 'do the authors mean ME, CFS, or both, and if the latter, using which criteria?' It's not a minor issue. Many studies on CFS have found that psychological and social factors predate onset and must be considered as potential influences. In contrast, I can only recall one or two studies associating ME and post-viral fatigue syndrome with a psychological aetiology. A history of child abuse has been noted in several studies on CFS but, to my knowledge, not in ME. ME, unlike CFS, can occur in epidemics. Studies following patients from the acute phase have found no abnormalities such as raised levels of cytokines etc, that differentiate those who recovered at six months and those who did not. Any abnormalities observed later could, therefore, be a result of variables such as the burden of illness (e.g. illness intrusiveness) or other complications. The confusion between ME and CFS has resulted in a mountain of inconsistent findings. As CFS covers a multitude of ills, sometimes the only thing the population has in common is profound fatigue. Low NK cell activity can be a result of stress, so its clinical significance in ME/CFS needs to be established. I welcome the immense amount of work that the authors have completed but perhaps the most important issue to be addressed, before we continue to evaluate the evidence, is to establish what we mean by ME and CFS and whether we are persuaded, given the differences identified by experts such as Prof. Jason, that they are one and the same. Only when we have tested the assumption of equivalence does it make sense to combine findings from studies on ME and CFS and compare the hybrid with diseases such as MS. In short, good science demands that we go back to basics, define terms, cast a critical eye over the findings and remain ruthlessly disapssionate. Goudsmit, EM, Shepherd, C., Dancey, CP and Howes, S. ME: Chronic fatigue syndrome or a distinct clinical entity? Health Psychology Update, 2009, 18, 1, 26-33. Updated: http://www.foodsmatter.com/me_and_cfs/cfs_me_causes_general/articles/goudsmit-me-clinical%20entity-10-12.html Goudsmit, EM., Stouten, B and Howes, S. Illness intrusiveness in myalgic encephalomyelitis. An exploratory study. Journal of Health Psychology, 2009, 14, 2, 215-221. http://hpq.sagepub.com/cgi/content/abstract/14/2/215?etoc Competing interests My professional judgement may be influenced by the fact that I was diagnosed with ME in the early 1980s. There is no diagnostic test for this disease but it feels like an infection and some of the lesser known symptoms are identical to those of MS. Due to the illness, I am no longer able to work as a scientist and offer readers a long list of references to support my arguments. For that, I apologise.