MGUS and multiple myeloma: what is the difference?

Both conditions involve plasma cells, which make antibody proteins. With MGUS, the abnormal protein is found but there is no evidence of related damage to organs such as the bones, kidneys or blood-producing marrow. Multiple myeloma is diagnosed when plasma-cell disease and related clinical or laboratory effects are present.

The distinction cannot be made from a symptom or one blood result alone. Clinicians consider the protein pattern, blood counts, kidney function, calcium, imaging when needed, and the overall examination. A diagnosis can change only after the relevant findings are reviewed together.

Attend the monitoring visits arranged for you and ask which results are being compared over time. Keep reports together, tell clinicians about new medicines, and report changes in bone comfort, energy, infections or urination. Monitoring is intended to identify a meaningful change early and does not mean that myeloma has been diagnosed.

For background, see [Multiple Myeloma](/conditions/multiple-myeloma/) and the explanation of [Follow-Up After Cancer Treatment](/treatments/survivorship-and-rehabilitation/post-treatment-surveillance/).

Seek prompt medical advice for ongoing bone pain, fractures after minor injury, unusual fatigue, repeated infections, easy bruising, swelling or a clear change in urine. Severe back pain with numbness or weakness, or difficulty controlling urine or stool, needs urgent assessment. These signs are not proof of myeloma, but they should not be ignored.

Ask: What findings support MGUS rather than myeloma? Which tests will track the difference? Do I need imaging or a haematology referral? What symptoms should I report immediately?