|Photomicrograph of bone marrow from patient with multiple myeloma.
Click to enlarge image.
Plasma cells from patients with myeloma are usually immature in appearance with centrally located nuclei, distinct nucleoli, and perinuclear vacuolization. There are also often multinucleated plasma cells.
Immunohistochemical analysis can verify monoclonality.
The plasma cells produce monoclonal IgG or IgA that can be detected through a characteristic serum protein electrophoresis pattern. Eighty percent of the patients have a complete monoclonal Ig in the serum and most of them simultaneously produce light chains in the urine (Bence-Jones protein). The light chain concentration in the urine is often so low that Hellers urinary test is negative.
Asymptomatic multiple myeloma
In asymptomatic multiple myeloma, the M-component is >30 g/l and/or plasma cells in bone marrow aspirate >10% without organ involvment related to myelomatosis.
Symptomatic multiple myeloma
In symptomatic multiple myeloma, the M-component in serum or urine (without volume requirement), monoclonal plasma cells in bone marrow aspirate or biopsy (without requirement of number) with organ injury or symptoms related to multiple myeloma (ROTI, or Related Organ or Tissue Impairment).
In solitary plasmacytoma, there is solitary bone destruction consisting of monoclonal plasma cells without other sign of multiple myeloma.
Plasma cell leukemia
Multiple myeloma where >20% of leukocytes in peripheral blood represent plasma cells; >2 x 109/L are plasma cells.
In about 1% of the multiple myeloma patients, there is no detectable monoclonal Ig (non-secretory myelomatosis). Immunofluorescence or immunohistochemical analysis of the bone marrow will then almost always demonstrate intracellular monoclonal Ig.
Light chain disease
In 20% of multiple myeloma patients, only light chain is produced. These light chain Ig do not stay in the blood serum, but are excreted through urine. Thus, it is usually not possible to see any monoclonal bands in the serum eletrophoresis. This type of myelomatosis is named “light chain disease”.
These light chains are toxic to the kidneys, therefore, many patients with this disease are referred to the hospital because of renal insufficiency. Patients referred to the hospital with renal insufficiency of unknown cause should be evaluated to exclude myelomatosis of light chain type with bone marrow aspiration and electrophoresis of urine.
There is a type of amyloidosis associated with monoclonal plasma cell proliferative disease, AL-amyloidosis. The main protein in this type of amyloid is larger or smaller N-terminal fragments of monoclonal light chain IG. These proteins are deposited in the tissue and affect the function of that organ. In this disease, there is often small amount of free light chains in the serum and/or urine that can be detected by sensitive methods. Bone marrow often demonstrates a slight increase in the number of plasma cells and no indication of bone lesions. It is important that these patients are treated as myeloma patients, even if they do not demonstrate typical myeloma findings.