MGUS: PART OF THE MULTIPLE MYELOMA CONTINUUM:
Just to emphasize that MGUS is on the same continuum with Multiple Myeloma, I have found two articles that both define MGUS as stage I multiple myeloma. I suspect that the reason that the term "MGUS" is more generally used is that in stage I, by definition, there is no more than 1 identifiable tumor. So by definition, the stage I condition is not yet multiple. It's stage 1 multiple myeloma, but without the "multiple" - yet. And another reason the term "MGUS" is more frequently used is to emphasize that stage 1 most often does not progress within the remaining lifespan. The "US" of "MGUS", standing for "undetermined significance" really empasises that fact. Another reason that "MGUS" is the preferred term is that patients with IgM MGUS are more likely to progress to Waldenstraum's Macroglobulinemia than to Stage II. Here are the articles.
http://cancer.nchmd.org/treatment.aspx?id=831 and:
This second article, on the Multiple Myeloma Research Foundation site, includes the Durie-Salmon and ISS criteria for staging, and as you will all see, your MGUS criteria also meet the stage I criteria. You will see that the bone lesions do not become multiple until stage II or stage III, and so that is when it is commonly referred to as "multiple myeloma." Note, however, that increasingly the B2-M test (ISS criteria) is being preferred over the Durie-Salmon criteria for purposes of staging.
http://www.multiplemyeloma.org/about_myeloma/2.05.html .