[evolve2017]

I see what you're implying with your UC/Crohn's reference, but it actually underscores why CFS is so hard of a diagnosis.

In UC/Crohn's, patients presented with recurrent bouts of bloody diarrhea in the absence of infectious symptoms, with possible associations of malabsorption, fistulas, and colon cancer. These are pretty straightforward things to diagnose and clearly represent pathology, irrespective of whether we can assign a name to them.

CFS includes symptoms that don't fall so far from the range of 'normal' human experiences, thus it's much harder to define syndromically.

IBS is an interesting choice for comparison, as it, like CFS, seems to be in part a psychiatric diagnosis at least as it relates to stress. Nothwithstanding, there are clear associations for IBS - chronic abnormal bowel movements and abdominal pain, neither of which is 'normal'.