Differential diagnostics are intended to differentiate multiple myeloma from other malignant diseases with bone marrow involvement, chronic inflammation conditions, and lymphoproliferative diseases (lymphoma).
A M-component with < 30 g/l and < 10 % plasma cells in bone marrow aspirate which is not accompanied by symptoms or sign of multiple myloma or other B-lymphoproliferative disease is called MGUS (monoclonal gammopathy of undetermined sigificance).
The differentiation between MGUS and asymptomatic multiple myloma is based on the size of the M-component and amount of plasma cells in the bone marrow. However, there is no indication for treatment until symptomatic multiple myeloma is present. The difference is therefore rarely of practical significance.
For MGUS, the M-component is almost never over 30 g/l for IgG and almost never over 20 g/l for IgA or IgM. There is usually a normal concentration of polyclonal immunoglobulins and almost never over 10% plasma cells in the bone marrow. The Bence-Jones protein is present much more commonly in multiple myeloma than MGUS.
MGUS is never accompanied by osteolytic lesions or anemia. A low concentration of M-component in an elderly person without symptoms should not be of concern if the patient does not have clinical symptoms. MGUS is relatively common (up to 2% in people over 50 and 3% in people over 70). Thus, most persons having M-protein in their serum have MGUS and not cancer of the bone marrow.
Other conditions where the M-protein may be present are:
- Solitary plasmacytoma
- B-cell non-Hodgkin lymphoma (including Waldenstrom macroglobulinemia)
- Chronic lymphatic leukemia
- Autoimmune disease such as SLE