In hematopathology, plasma cell neoplasms are classified into:
Non IgM Monoclonal Gammopathy of Undetermined Significance (MGUS - precursor)
Monoclonal immunoglobulin deposition disease
Systemic light chain deposition disease
Plasma cell myeloma (Multiple myeloma)
Plasma cell leukemia
Non secretary myeloma
Solitary plasmacytoma of bone
Plasma cell myeloma
Primary bone malignancies are rare. (1%)
Predisposition to Old aged (>50years) and males.
Plasma cell Myeloma
Clonal bone marrow plasma cells ≥ 10% of all plasma cells.
Biopsy proven 'Plasmacytoma'
≥1 from the following myeloma defining events
CRAB criteria for End organ damage
Serum Calcium > 11mg/dL
Renal insufficiency denoted by
Serum Creatinine >2mg/dL
Anemia, Hb < 10g/dL
Bone shows ≥ 1 osteolytic lesions
Positive biomarkers for malignancy:
Clonal bone marrow plasma cells ≥ 60%.
Involved light chains >100 times of uninvolved.
MRI shows >1 focal lesions.
Serum M protein >30g/dL; urinary M protein > 500mg/24hr.
Clonal BM plasma cells 10 - 60% of all plasma cells.
No myeloma defining events / amyloid.
Clinical features and investigations
Bleeding due to thrombocytopenia
Compression fracture of vertebrae
Involvement: Vertebrae > Ribs > Skull > Pectoral and Pelvic girdles > Long bones
Tumor mass in extramedullary involvement - Can cause spinal compression or peripheral neuropathy
End organ damage leads to components of CRAB criteria
Diminished normal plasma cell immunoglobulin secretion leads to infections
Skin may have plasma cell infiltration and purpura.
97% of PCMs secrete abnormal light chain or heavy chain of one type of immunoglobulin (IgG > IgA > IgD > IgE > IgM)
If IgG, it will be >30g/dL. And if TgA, it will be >20g/dL.
3% of PCM won't secrete this. [ Non secretary myeloma ]
Hyperuricemia and hypoalbuminemia
Soft gelatinous fish flesh hemorrhagic tissue
Leukoerythroblastic blood picture
If clonal plasma cells are seen in peripheral blood as >20% of total WBC (absolute counts >2000/microL), it is Plasma cell leukaemia.
Bone Marrow Aspirate
Total plasma cells > 90% of nucleated cells
In which, clonal plasma cells are ≥ 10% of all plasma cells.
Oval with abundant basophilic cytoplasm
Round eccentric nucleus.
Perinuclear hof due to ribosomes
Immature plasma cells
Cells with endoplasmic reticulum containing crystalline clonal immunoglobulins (May be seen in reactive conditions also).
Mott cells / Morula cells - Pale blue cells with bunch of grape like cytoplasm
Russel bodies - Cherry red refractile round bodies in cytoplasm
Flame cells - Glycogen rich IgA in cytoplasm
Pseudo-Gaucher cells - fibrils in cytoplasm
Thesaurocytes - similar to pseudogaucher cells
The major limitation of aspirates is that, focal distribution of plasma cell clusters may lead to inadequate findings. Plasma cells in aspirate may be <10% if aspiration missed the clusters. Hence biopsy is recommended.
Bone Marrow Biopsy
The tumour mass may be biopsied by the surgeon from bone without any accompanied blood studies.
Plasma cells constitute 30% of the volume of marrow
Involvement may be singly scattered cells to focal interstitial clusters. Advanced diseases will have diffuse involvement.
Small cell variant mimics a Mantle cell lymphoma.
Mature plasma cell
Mott cell / Morula cell
Mature and Immature plasma cells