Did you notice that mastocytic enterocolitis, cutaneous mastocytosis, mastocytosis, and systemic mastocytosis were all listed separately?  Didn't have time to see if there were more.

Except for the general term, mastocytosis, the others specifically refer to different primary problems.  M.E. refers to a problem confined to the GI tract, and it can be caused by too many clonal or non-clonal mast cells.  Cutaneous, of course, refers to a problem predominantly in the skin, while systemic means the entire body.

I think the separate names are intended to be more specific diagnoses than a general term, especially since the treatment varies somewhat for each.  I agree that the same basic mechanism probably causes them, in that some cases show a gene defect and some don't, while all of them indicate mast cell activation.  They all fall under the broadest category, Mast Cell Disorders.

Good point.  Diagnosing is getting much better, so sometime enough people will be diagnosed to take the disease off the list.  I think this will happen with mastocytic enterocolitis.  My doctor alone has verified over 400 cases it it by biopsy.