Multiple myeloma vs MGUS
How to tell Multiple myeloma and MGUS apart when a board question makes them look alike.
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Any CRAB end-organ damage with a monoclonal protein separates multiple myeloma from MGUS.
Side by side
Monoclonal plasma-cell disorder with end-organ injury such as lytic bone pain, anemia, kidney dysfunction, or hypercalcemia.
Stable monoclonal protein without CRAB end-organ damage and with low plasma-cell burden.
Clonal plasma cells expand in marrow, secrete monoclonal immunoglobulin, and cause organ injury through bone resorption and light-chain toxicity.
MGUS is a low-level plasma-cell clone that produces monoclonal protein but has not yet caused tissue damage.
Diagnosis is supported by marrow plasma cells >=10% or plasmacytoma plus myeloma-defining events, including calcium >11 mg/dL, creatinine >2 mg/dL, hemoglobin <10 g/dL, or lytic lesions on imaging.
MGUS typically has M-protein <3 g/dL, marrow plasma cells <10%, and no CRAB findings or lytic lesions.
The trap
Assuming all monoclonal spikes are benign misses symptomatic myeloma; back pain with anemia or renal decline should trigger marrow and skeletal evaluation rather than surveillance only.
The repair move
Next best step: confirm end-organ myeloma with serum free light chains, urine protein electrophoresis, bone marrow biopsy, and skeletal imaging, then start hydration and oncology-directed induction therapy with bone protection.
Try a free question
CoreA 67-year-old woman has SPEP monoclonal protein 2.1 g/dL found incidentally. Hemoglobin is 12.8 g/dL, creatinine 0.9 mg/dL, calcium 9.2 mg/dL, and skeletal imaging is normal. What is the most likely diagnosis?
Show answer and explanation
Answer: C. MGUS. Low-level monoclonal protein without CRAB findings is most consistent with MGUS.
Why the other choices are tempting
- A. Incorrect because there is no end-organ injury or high tumor burden to support multiple myeloma.
- B. Incorrect because there is no IgM hyperviscosity syndrome data supporting Waldenstrom disease.
- D. Incorrect because normal calcium and monoclonal spike do not indicate primary hyperparathyroidism.
- E. Incorrect because there are no organ findings such as nephrotic syndrome, restrictive cardiomyopathy, or neuropathy suggesting AL amyloidosis.
Flashcards
Tap a card to flip it.
What finding converts a monoclonal gammopathy from MGUS to symptomatic multiple myeloma?
A myeloma-defining end-organ injury such as CRAB features or biomarker-defined high tumor burden converts it to multiple myeloma.
Which M-protein threshold is typical for MGUS rather than multiple myeloma?
MGUS usually has M-protein below 3 g/dL with marrow plasma cells below 10% and no organ injury.
Quick answers
What is the fastest way to tell Multiple myeloma from MGUS?
Any CRAB end-organ damage with a monoclonal protein separates multiple myeloma from MGUS.
What is the key clue for Multiple myeloma?
Monoclonal plasma-cell disorder with end-organ injury such as lytic bone pain, anemia, kidney dysfunction, or hypercalcemia.
What is the key clue for MGUS?
Stable monoclonal protein without CRAB end-organ damage and with low plasma-cell burden.
What is the common trap with Multiple myeloma vs MGUS?
Assuming all monoclonal spikes are benign misses symptomatic myeloma; back pain with anemia or renal decline should trigger marrow and skeletal evaluation rather than surveillance only.