The M-Band

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Figure 1. Each plasma cell produces a different type of antibody. Normal γ globin band is depicted in the left column. The plasma cell numbers are normal and each produces an antibody with a different amino acid structure and electrophoretic mobility. Patients with monoclonal gammopathy have expansion (increase number) of a plasma cell clone (red in the diagram) resulting in the production of a disproportionate large amount of immunoglobulin from one type of plasma cell. This results in the M Band (see below). Patients with polyclonal gammopathy have an expansion (increased number) of plasma cells. This is usually occurs in response to infection/inflammation that result in production of a diversity of antibodies. The diversity is reflected in increase in the γ but as no one clone dominates the sharp M band is not seen.

What is an M-Band?

Immunoglobulins are antigen binding molecules secreted by plasma cells. Immunoglobulins bind antigens and play a role acquired immunity. Plasma cells develop from antigen exposed B-lymphocytes. The process of maturation of lymphocytes involves inducing mutations in region of the immunoglobulin gene that encodes for antigen binding regions, the hypervariable regions. This makes the DNA and consequently the amino acid sequence of the immunoglobulin secereted by a plasma cell unique. This is true even when two plasma cells make antibody against the same antigen or antigenic epitope (see figure 1).

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Figure 2. The serum protein separate into many bands on electrophoresis. The albumin is a dark band closest to the anode. This is followed by the α1, α2, β and γ bands. The immunoglobulin are mainly found in the γ globulin band but some may be found in the β globin band. The electrophoretic mobility of a molecule depends on the charge it carries which in turn depends on the amino acid sequence. Amino acid sequence determines the antigen specificity and differs between antibodies resulting in a slight variation in electrophoretic mobility of immunoglobulins and resulting in the γ region being a broad band.

The amino acid sequence determines the charge on the immunoglobulin. The electrophoretic mobility is determined by the charge. Majority of the immunoglobulins move to the γ-globulin fraction of serum proteins, some move with β-globulin. The γ-globulin band is a wide electrophoretic band reflecting the diversity in electrophoretic mobility of immunoglobulins arising from the diversity in amino acid sequences (figure 2).

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Figure 3. Patinets of monoclonal gammopathies have an expansion of one clone of plasma cells. This reflects in production of a disproportionally large amount of immunoglobulin with identical electrophoretic mobility resulting in a dense band with in γ globin region

Patients of monoclonal gammopathies have clonal expansion of plasma cells. The cells of a clone have identical DNA and produce identical immunoglobulin molecules. When the clone grows to level that it forms a significant proportion of the plasma cell pool the immunoglobulin it produces forms a significant proportion of the total serum immunoglobulins. The identical electrophoretic mobility of molecules produced by the clone results in a disproportionately large number of immunoglobulin concentrating to a point on electrophoresis forming a band.  This is known as the M band.  Lymphoma cells, notably those of lymphoplasmacytic lymphoma, can secrete immunoglobulin and are associated with an M band for similar reasons.

Diseases associated with an M-Band

The M-Band is a serum marker for plasma cell dycrasias and Waldenström macroglobulinemia. IgM and non-IgM (mainly IgG and IgA) monoclonal bands have differing clinical implications. The former is more commonly associated with lymphoproliferative disease and the latter with plasma cell dycrasias. The presence of an M band only indicates a clonal expansion of immunoglobulin producing cells. It does not indicate malignancy. The diagnosis of malignancy is made by features that suggest end organ damage. The absence of end organ damage indicates a premalignant disease including monoclonal gammopathy of uncertain significance (MGUS), soldering multiple myeloma or smoldering Waldenström macroglobulinemia.  The evidence of end-organ damage includes

  1. non-IgM Monoclonal Gammoathies: CRAB (elevated calcium, renal involvement, anaemia and osteolytic (bone) lesions) creatinine,
  2. IgM Monoclonal Gammapathies: Anemia, constitutional symptoms, hyperviscosity, lymphadenopathy, or hepatosplenomegaly that can be attributed to the underlying lymphoproliferative disorder if diagnosis is Waldenström macroglobulinemia or CRAB (elevated calcium, renal involvement, anaemia and osteolytic (bone) lesions) creatinine if the diagnosis of IgM myeloma

False positive M-Band

The presence of M band indicates presence of a clonal expansion of plasma cells. When end organ damage co-exists with M band a diagnosis of a malignancy (multiple myeloma or Waldenström macroglobulinemia) is made. In the absence of end organ damage the diagnosis of a premalignant disease is made. Proliferation a of plasma cells are seen in infections/inflammation. These are polyclonal and result in s polyclonal gammopath. They do not result in the presence of an M-band.




Staging of Multiple Myeloma

Cancer is a heterogenous disease in terms of survival. Cancer staging is a method to classify patients according to prognosis. More advanced stages are associated with a worse prognosis. Patients with a poorer prognosis need to treated more aggressive. Non-haematological cancers are stages by the TNM staging. This system relies on the size of primary tumour, number of regional nodes involved and the presence or absence of distant metastasis to stage cancers. This scheme of of things is inappropriate for haematological cancers because

  1. The T Stage: Either it may be difficult to define the primary or in case of lymphoma the lymph node disease may be the primary
  2. The N Stage: Lymph node are not involved except in lymphoma where they are the primary site.
  3. The M Stage: Other than lymphomas haematological malignancies are “disseminated” at presentation with either the disease in the blood, as is the case with leukaemia, or in the bone marrow in case of multiple myeloma

These differences have resulted in evolution of staging/prognostic systems distinct from the TNM when one deals with haematological malignancies.

Multiple myeloma is a plasm cell neoplasm. It is characterised by a monoclonal protein in the serum and/or the urine, osteolytic lesions, anaemia, hyercalcaemia and renal failure. In the 1960s and 1970s these and other features of the disease were found to predict prognosis. Durie and Salmon in 1975 proposed the first staging system for multiple myeloma using type and amount of the monoclonal protein, haemoglobin, serum calcium and serum creatinine. They defined three stages of multiple myeloma I, II and , III. The tumour load increased as the stage increased. Each stage was further divided into substage A and B depending on the serum creatinine. The Durie-Salmon staging system is as follows:

    1. Stage I (All of the below)
      1. Hemoglobin value >10 g/dL
      2. Serum calcium value normal or =12 mg/dL
      3. Bone x-ray, normal bone structure (scale 0) or solitary bone plasmacytoma only
      4. Low M-component production rate (IgG < 5 g/dL; IgA < 3 g/dL; Bence Jones protein <4 g/24 hr)
    2. Stage II – Neither stage I nor stage III
    3. Stage III  One or more of the following:
      1. Haemoglobin < 8.5g/dL
      2. Serum calcium > 12 mg/dL
      3. Advanced lytic bone lesions (scale 3)
      4. High M-component production rate – IgG  >7 g/dL; IgA >5 g/dL; Bence Jones protein >12 g/24 h

Durie-Salmon sub classifications (either A or B)
A: Relatively normal renal function (serum creatinine value <2.0 mg/dL)
B: Abnormal renal function (serum creatinine value =2.0 mg/dL)

This system was widely adapted but the assesment of osteolytic lesions is subjective resulting in a poor reproducibility. Several attempts to improve the system that did not gain widespread acceptance were proposed.

After the introduction of the Duris-Salmon system other prognostic factors emerged. These included serum albumin, C-reactive protein, proliferation indices for bone marrow plasma cells (flowcytometery and S-phase fraction), bone marrow plasma cells and serum β2-microglobulin levels. Serum β2-microglobulin emerged as a good predictor of prognosis. 2005 the international staging system for multiple myeloma was proposed. The ISS stage was determined by only two objectively assessable parameters, serum β2-microglobulin and serum albumin. The staging system was as follows (J Clin Oncol May 20, 2005 vol. 23 no. 15 3412-3420)

  1. Stage I, Serum β2-microglobulin less than 3.5 mg/L and serum albumin ≥ 3.5 g/dL
  2. Stage II, neither stage I nor III
  3. Stage III, Serum β2-microglobulin ≥ 5.5 mg/L

The median survivals by stage are as follows: stage I 62months, Stage II 44 months and stage III 29 months.

Chromosomal studies, conventional karyotyping and interphase chromosomal studies using fluorescent In-situ hybridisation (FISH), identified translocations that adversely affect the out come of myeloma. These included del(17p), translocation t(4;14)(p16;q32) and translocation t(14;16)(q32;q23). In 2015 the chromosomal translocation were incorporated in the ISS and a revised system (R-ISS) was proposed (JCO.2015.61.2267)

The revised staging system is as follows

  1. R-ISS I: Serum β2-microglobulin level < 3.5 mg/L and serum albumin level ≥ 3.5 g/dL), no high-risk chromosome anomalies – [del(17p) and/or t(4;14) and/or t(14;16)] and LDH level less than the upper limit of normal range.
  2. R-ISS II: Nether R-ISS I nor R-ISS II
  3. R-ISS III: ISS stage III (serum β2-microglobulin level > 5.5 mg/L) with either high-risk chromosomal anomalies or high LDH level

Median OS not reached R-ISS, 83 months for R-ISS II and 43 months for R-ISS III. The improved median survival for all stages in R-ISS is a reflection of the efficacy of drug therapy of myeloma.

Bisphosphonate Associated Osteonecrosis

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Bisphosphonate Associated Osteonecrosis of the Mandible This 62 year old gentleman, a patient of multiple myeloma, on treatment with 4 weekly zolandronate presented with jaw pain. Examination showed a exposed bone. A diagnosis of ONJ was made.

Osteoclast mediated absorption of bone is responsible for skeletal morbidity associated cancer. Bisphosphonates target the osteoclast and reduce skeletal events. Osteonecrosis of the jaw is an uncommon but serious adverse effects of bisphosphonate therapy.

Bisphosphonate associated osteonecrosis is defined as an area of exposed bone that does not heal for 8 weeks in a patient who has received bisphosphonates, does not have local malignancy and has not received craniofacial radiation. The patients present with jaw pain and examination reveals exposed bone. The mandible is more often involved than the maxilla.

ONJ is more common with intravenous bisphosphonates (1-4%), more frequent therapy and prolonged therapy. Many patients have a history of a dental procedure before osteonecrosis. It is very rare with oral bisphosphonates. The mechanism of osteonecrosis is not understood.

ONJ is treated by conservative measures including antibiotics and antibacterial mouth rinses. Superficial debridement may be of help in selective cases. There are concerns that surgical intervention may worsen the symptoms. Patients on bisphosphonated who need to undergo a dental procedure are usually advised to discontinue bisphosphonates 3 months before the procedure. This recommendation is based on experience rather than and scientific evidence. Denosumab, another anti-osteoclast agent has also been associated with ONJ.

Multiple Myeloma

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Normal plasma cells are 15-20 μm in diameter, have an eccentric nucleus and a pale blue cytoplasm. there is a perinuclear halo which corresponds to the Golgi apparatus. The cytoplasm may show vacuoles.

The nucleus has clumped chromatin. The cartwheel or clock-faced pattern is less evident on smears than on histological sections. It is normal for cccasional cells to have have two or more nucleus.

The figure above shows plasm cells from a patients with multiple myeloma that are farly normal. Plasma cells morphology in patients with multiple myeloma ranges from normal to moderate to severe dysplasia.

Conventional Radiology in Multiple Myeloma

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There are four monoclonal gammopathies

  1. Monoclonal gammopathy of uncertain significance (MGUS)  defined as monoclonal component <3g/dL and bone marrow plasma cells less than 10% and no end organ damage.
  2. Asymptomatic myeloma defines as monoclonal component ≥ 3g/dL and/or bone marrow plasma component ≥10% in the absemce of end organ damage.
  3. Multiple myeloma Bone marrow plasma cells ≥ 10% in the presence of end organ damage attributable to the plasma cell proliferation.
  4. Solitary plasmacytoma which may be further divided into osseous and non-osseous solitary plasmacytoma.

End organ damage includes

  1. Osteolytic lesions
  2. Anaemia defined as fall in haemoglobin by more than 2g/dL below normal or a haemoglobin < 10g/dL
  3. Renal failure defined as serum creatinine >2mg/dL and and estimeted creatinine clearance <40 ml/min.
  4. Hypercalcaemia defined as serum calcium > 11.5g/dL.

Osteolytic lesions are most commonly assessed by a skeletal survey. The skeletal survey in patients with multiple myeloma includes

  1. Frontal and lateral view of the skull
  2. Frontal and lateral views of the cervical, thoracic and lumbar spine
  3. A coned-down frontal view of the dens axis
  4. Frontal views of the rib cage
  5. Frontal Views of both humeri
  6. Frontal Views of both femora
  7. Frontal Views of both knees
  8. Frontal Views of the pelvis.

About 80% of the patients with multiple myeloma have lesions apparent on skeletal survey. Vertebrae are involved in 66%, ribs in 45%, skull in 40%, pelvis in 30% and long bones in 25%.  Other estimates have put the involvement at spine 49%, skull 35%, pelvis 34%, ribs 33%, humori 22%, femora 13% and mandible 10%. The figures may differ from report to report  but it is clear that the axial skeleton and proximal long bones are the commonest sites of involvement in myeloma. These correspond to areas of active marrow in an adult. The utility of conventional radiology in evaluation of multiple myeloma is limited by the fact that al least 30-50% of the bone must be lost for the lytic lesions to be visible. Myeloma cell origin protein DKK1 results in loss of cells of stem cells of the osteoblastic lineage. The osteolytic lesions of multiple myeloma may not heal despite treatment. Skeletal survey is not only important for diagnosis. There is an association between number of lytic lesions and tumour load. Number of lytic lesions determines stage by the Durie-Salmon criteria but is not needed for the international staging system.

The images show lytic lesions observed in patients with multiple myeloma.


Multiple myeloma – Involvement of tibia and fibula

Figure 1. Protein electrophoresis showing M Band in the gamma globulin region

A 66 year woman presented with backache without evidence of spinal cord compression. The MRI showed a hyper intense signal in the body of the C2, D9, D12 and L3 vertebrae. The D11-12 disc was involved with an associated soft tissue component. A skeletal survey showed punched out lytic lesions in the skull, pelvis both femora, right tibia and fibula. A protein electrophoresis showed a 2.9g/dL monoclonal band in the gamma region. immunofixationelectrophoresis showed the band to be of IgGλ type. The λ free light chain was 443mg/L (normal 5.71-26.30 mg/L) and κ was 22mg/L (3.30-19.40 mg/L) with a free light chain ratio of 20. A bone marrow aspiration showed 50% plasma cells with 12% immature. Therapeutic options were discussed with the patient and as she did not want injectable she was initiated on treatment with a combinations with melphalan, prednisone, and lenalidomide.

Figure 2. X-ray skull showing punched out lesions

Figure 3. Lateral view of the skull showing punched out lesions

Bones commonly involved by multiple myeloma include spine 49%, skull 35%, pelvis 34%, ribs 33%, humori 22%, femora 13% and mandible 10%. Tibia (see below) is rare and fibula rarer.

Figure 4. Lytic lesion in the tibia and fibula