Definitionally, the CFS criteria never require PEM and other hallmark criteria. But PEM is a hallmark of ME. Because of these definitional differences, the IOM explicitly stated that "a diagnosis of CFS is not equivalent to a diagnosis of ME." In my opinion, to untangle this mess, these two terms need to be separated and there is ample evidence to justify that. In the proposal that Suzy Chapman and I submiitted on ICD-11 for these terms, we recommended that these terms be separated for the same reason.
I really appreciate and share the concern with adding to the existing confusion of terminology. But in the US, medical education providers, at least one medical society, and reportedly some doctors have started to use the term "SEID."
Some people have said that while the term "SEID" was recommended, it was never officially endorsed. HHS itself is using the term "ME/CFS" in its material. But HHS does not have the authority to tell the medical community that they must do so as well. And NCHS, the group managing the ICD-10-CM, has stated that if the term "SEID" is being used by medical providers, then they must provide a code for it.
If a code is to be added, then I'm only aware of two options: 1) equate it to one of the other 5 codes - e.g. CFS or ME or 2) give it a separate and distinct code.
If a code is not added for SEID, then what code do the medical providers use if they are using the term SEID?
IMO, this is complicated mess for which there is no simple solution in the short term.