Plasma cell disorders: MGUS to myeloma
- Topic
A clone of plasma cells makes one antibody (an M protein). Some clones stay quiet for life; others become myeloma or deposit amyloid.
What it is
Plasma cell neoplasms and related disorders share a clone of terminally differentiated B cells that secretes a single complete or partial immunoglobulin, the M protein. The spectrum runs from the common, symptom-free MGUS through smouldering myeloma to multiple myeloma, with solitary plasmacytoma as a localized form. Lymphoplasmacytic lymphoma secretes IgM and causes Waldenström macroglobulinaemia. Light chains from a small clone can fold into AL amyloid, and heavy-chain disease secretes heavy-chain fragments only.
Step by step
- A post-germinal centre B cell or plasma cell acquires a translocation or hyperdiploidy.
- The clone settles in the marrow and secretes its M protein: a spike on electrophoresis.
- In MGUS the clone stays small and causes no damage.
- New mutations (MYC, RAS, NF-κB pathway) enlarge the clone and give bone, kidney and marrow damage: myeloma.
- Some light chains misfold into amyloid fibrils regardless of clone size.
The plasma cell spectrum
| Disorder | Clone | M protein | Organ damage | Course |
|---|---|---|---|---|
| MGUS | Small marrow clone | Low level | None | Progresses at about one percent per year |
| Smouldering myeloma | Larger marrow clone | Higher | None | Higher risk; can stay silent for years |
| Multiple myeloma | Diffuse marrow and bone masses | High; IgG or IgA, free light chains | Bone lesions, hypercalcaemia, kidney, anaemia | Treatable, rarely cured |
| Solitary plasmacytoma | One mass in bone or soft tissue | Low or absent | Local | Bone lesions usually progress to myeloma |
| Lymphoplasmacytic lymphoma (Waldenström) | Lymphocytes, plasmacytoid cells and plasma cells | IgM | Hyperviscosity, cryoglobulins, neuropathy | Indolent |
| AL amyloidosis | Often small | Light chains, usually λ | Heart, kidney, nerve, gut deposits | Depends on the heart |
Markers
- CD138
- CD38
- κ or λ restriction
- MYD88 L265P
Clinical notes
- Hyperviscosity: blurred vision with tortuous retinal veins, headache, bleeding and confusion; plasmapheresis removes intravascular IgM quickly.
- Nephrotic-range proteinuria or a thick stiff heart in an older adult should prompt a search for AL amyloid.
In the lab
- Serum and urine protein electrophoresis with immunofixation identify the M protein; serum free light chains measure the κ:λ ratio.
- Congo red staining with apple-green birefringence confirms amyloid.
Test yourself
Think of the answer, then tap the question to see it.
At what rate does MGUS progress to a symptomatic plasma cell neoplasm?
About one percent per year.
Which mutation is found in nearly all lymphoplasmacytic lymphomas?
MYD88 L265P.
Why does Waldenström macroglobulinaemia cause hyperviscosity but rarely bone lesions or kidney failure?
The large pentameric IgM thickens the blood, while the tumour does not cause bone resorption and secretes few free light chains.
Elsewhere in DurgiPedia
- Plasma proteins and electrophoresis
- Immunoglobulins (antibodies)
- B cell and plasma cell
- Antibody structure and isotypes (IgG, IgA, IgM, IgE, IgD)
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Plasma Cell Neoplasms (Including Multiple Myeloma) Treatment (PDQ®)–Patient Version (National Cancer Institute (NCI), 2026); Waldenström macroglobulinemia: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Primary amyloidosis: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.