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Questions about myeloma and MGUS

Example exam questions and answers about myeloma and MGUS (monoclonal gammopathy of undetermined significance) – for doctors and medical student exams


Is there a fundamental difference between MGUS and myeloma?

  • No. In both MGUS and myeloma, there is a clonal population of plasma cells in the bone marrow, which share an abnormal immunophenotype (CD38+ CD138+ CD45- CD19- CD11a-).
  • The difference is in the burden of disease (<10%, or >10% plasma cells in marrow), and hence the presence of complications. However many patients with MGUS only progress very slowly and it may take years for myeloma to develop, which justifies the different diagnostic categories.

Is a polyclonal raised IgG level evidence of myeloma?
  • No. Polyclonal raised immunoglobulins are seen in various inflammatory states, but do not indicate a primary plasma cell disorder such as myeloma, MGUS or amyloidosis.
Is a bone scan a useful investigation in myeloma?
  • No. The isotopes used in bone scans to detect metastatic solid organ cancers, such as breast and prostate, are taken up in response to osteoblast activity.
  • In myeloma only osteoclasts are stimulated, so the lesions do not appear on bone scans. The skeletal imaging modalities of choice are MRI or CT, to detect lytic lesions.
Does alkaline phosphatase go up in myeloma?
No. Again it is secreted by osteoblasts, not osteoclasts, so is not raised in myeloma bone disease, although it is in the presence of bone metastases from solid organ primaries.
How is it determined whether end-organ damage is attributable to myeloma?

  • This sometimes involves a degree of judgement, if for example there are multiple possible causes of anaemia.
  • Myeloma kidney disease can usually be demonstrated on a renal biopsy, though this is not always necessary, and is much more likely in the presence of very elevated serum free light chains (>1000 mg/L).
  • Discrete bony lytic lesions are easily attributable to myeloma, but more diffuse bone density loss may be due to osteoporosis.


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