Chapter 21

　 Monoclonal Gammopathies

Wu Jianmin

1.Which Patients Should be Evaluated for the Presence

of an M-Protein

2.What Types of Specimens Should be Studied, and

How Often Should They be Used to Follow Patients

with M-Proteins

3.Which Laboratory Methods should be used to Detect,

Identify, and Follow M-Proteins

GUIDELINES FOR EVALUATING MONOCLONAL GAMMOPATHIES

1.Myeloma

2.Immunoglobulin Isotypes in Multiple Myelorna

3.Waldenström's Macroglobulinemia

4.Monoclonal Gammopathy Of Undetermined

Significance.

5.B-Cell Neoplasms

6.Amyloidosis

DISEASE STATES

A monoclonal gammopathy is the protein product of

a single clone of plasma cells.

Although the term "monoclonal gammopathy"

often has been used to designate the proteins produced

by the malignant cells in multiple myeloma and other

B-cell lymphoproliferative lesions, such as

Waldenström's macroglobulinemia, a monoclonal

gammopathy also may be the product of a "regulated"

cell.

Factors to consider when evaluating an M-protein

include the quantity of the M-protein, the fluid in

which it is found (serum versus urine), and the

chemical type of the M-protein (light chains will

more likely be found in the urine than in the serum).

The term M-protein is used in the literature to

describe the monoclonal gammopathy. Although it

has been variously used for "monoclonal component,

mveloma prorein, and macroglobulin protein," the

recently published guidelines for evaluating

monoclonal gammopathies recommend the use of the

term "M-protein".

Which Patients Should be Evaluated

for the Presence of an M-Protein

M-proteins are found in the serum and/or urine of

patients with a wide variety of clinical conditions.

The occurrence and clinical symptoms of these

conditions vary widely (Table 21-1).

TABLE 21-1 CONDITIONS ASSOCIATED WITH THE PRESENCE OF AN M-PROTEIN

 

Multiple myeloma Back pain, osteolytic lesions, fatigue, elevated sedimentation rate, nephrotic syndrome, infections, anemia, elevated calciumWaldenström's Fatigue, elevated sedimentation rate, macroglobulinemia dizziness, anemia, hyperviscosityB-Lymphoproliferative Fatigue, anemia, lymphadenopathy, disorders lymphocytosisAmyloid (AL), light chain Nephrotic syndrome, congestive deposition disease heart failure,carpal tunnel syndromeNeuropathy and M-protein Peripheral sensory and/or motor neuropathyMonoclonal gammopathy of No symptoms related to the M-proteinundetermined significance (MGUS)

Condition Clinical Features

Traditionally, the size of the M-protein has been helpful in

determining the significance for the patient. Typically, a large

quantity of M-protein (greater than 2 G/dL) is more likely to

be associated with myeloma, whereas, a small quantity of M-

protein may be associated with monoclonal gammopathy of

undetermined significance (MGUS) . Yet, several important

conditions associated with small quantities of M-proteins may

be overlooked if these M-proteins are not recognized (Table

21-2).

Condition Associated Feature

Light chain disease 15% of cases of multiple myeloma are light chain diseaseAmyloid (AL) 20% have multiple myeloma or Waldenström's macroglobulinemiaHeavy chain disease Alpha chain disease is rare in United States Gamma chain disease is associated with B-lymphoproliferative disordersM-protein associated neuropathy Must do Immunofixation of serum to rule outCryoglobulin type II Associated with Hepatitis CSolitary plasmacytoma Tiny or no M-protein in serumB-Lymphoproliferative disorder Often with overall gamma suppressionMGUS The most common cause of serum M-proteins

 

TABLE 21-2 CONDITIONS WITH RELATIVELY SMALL QUANTITIES OF M-PROTEIN IN SERUM

What Types of Specimens Should be Studied, and How Often Should They be Used to Follow Patients with M-Proteins

The initial evaluation of a patient with clinical

features suggesting the presence of an M-protein

should include a serum and urine electrophoresis

using high-resolution methods (Fig. 21-1).

Fig. 21-1. Specimens and evaluation for detecting monoclonal gammopathies.

If the serum protein electrophoresis is negative, and

there is a low index of suspicion, one may wish to

look for other causes of the symptoms before

performing an immunofixation (IFE). However, if

the clinical suspicion is high, an IFE should be

performed even when no M-protein is seen on the

screening electrophoresis.

If an M-protein is found on the screening

electrophoresis, an IFE must be performed to

identify the M-protein. This identification serves

several purposes.

First, it rules out a false positive due to some

other protein that may mimic an M-protein on

serum protein electrophoresis (Table 21-3).

Table 21-3 ． proteins that may mimic an M-protein Fibrinogon C3 Variant Transferrin variant Beta-1 lipoprotein Antibiotic band on capillary zone electrophoresis

Second, because IFE is more sensitive than screening

electrophoresis, it may identify a second M-protein (often a

monoclonal free light chain that accompanies the intact

molecule in the serum).

Third, it identifies the M-protein for comparison with

subsequent samples from the patient. If there is no change in

the migration of the identified M-protein on subsequent

samples, there is no need to perform further IFE studies.

For serum, the best measurement of the M-protein

is achieved by performing high-resolution

electrophoresis and measuring the amount of

protein below the spike (Fig. 21-2).

Fig.21-2. Capillary zone electropherogram with M-protein. M-proteins should be measured integrating the area under the peak.

For the urine, it is important to follow the

monoclonal free light chains and not the intact M-

protein immunoglobulin that may be found in the

urine. The prognosis and threat to the kidney is

mainly due to the amount of monoclonal free light

chain and not due to the intact M-protein.

The panel agreed that the term "Bence Jones

protein" has been somewhat confusing in this

regard. Bence Jones protein only refers to the

monoclonal free light chains, not to the intact

monoclonal immunoglobulins.

Which Laboratory Methods should be used to Detect, Identify, and Follow M-Proteins

The panel was unanimous that the laboratory

should use a high-resolution electrophoretic method

in the initial evaluation of serum and urine. A high-

resolution method is one that permits a crisp

separation of transferrin and C3 in the beta region

(Fig. 21-3).

Fig.21-3. high-resolution electrophoresis with M-protein (top).normal (middle).And polyclonal patterns. The gel or CZE pattern should provide crisp separationof the beta-1 (transferrin) band from the beta-2 (C3) band.

immunofixation with an IgA kappa M-protein. Note the small M-protein band (arrow) in the SPE lane. The IgA and kappa restrictions are obvious.

DISEASE STATES

Multiple myeloma is the most common malignant cause for

the presence of an M-protein in serum or urine. This disease

is because of a malignant proliferation of a clone of B

lymphocytes that manifests predominantly as plasma cells.

Note that multiple myeloma often is considered to be a

condition of malignant plasma cells. In fact, the malignancy

involves the entire B-cell lineage but manifests mainly as

malignant plasma cells.

Myeloma

The isotypes of immunoglobulins seen in multiple myeloma

largely reflect their prevalence in normal serum.

IgG myeloma proteins predominate. They are almost always

monomers weighing 160,000 daltons. It is rare that IgG

myeloma proteins produce significant problems with

hyperviscosity.

IgE myeloma is extremely rare and can occur as monomers or

as polymers with variable molecular weight.

Immnunoglobulin Isotypes in Multiple Myelorna

IgA myeloma may be difficult to diagnose on occasion

because IgA tends to migrate in the P region. Therefore,

early in its course, the other beta region bands may mask

the IgA myeloma. C3, transferrin, or fibrinogen from an

inadequately clotted sample of blood or an inadvertently

examined sample of plasma may obscure the presence of

an IgA myeloma M-protein.

IgD myelomas also may be missed because the amount of

M-protein may be relatively small. If one is using the older

five-band electrophoresis techniques, a normal alpha 2 or

beta region band may hide the small IgD component. Also,

as discussed later, when radial immunodiffusion plates

perform quantification, at least two dilutions of the

patient's serum must be performed to avoid antigen excess.

Alpha heavy-chain disease is extremely uncommon in the

western world. In the Middle East and Mediterranean

regions, an unusual disease called a heavy-chain disease

occurs. The tissue distribution of the plasma cells in this

lesion roughly parallels that for the normal distribution of

IgA along the gastrointestinal tract and other mucosal

surfaces.

Patients with Waldenström's macroglobulinemia suffer

from complications of hyperviscosity from the presence of

large amounts of circulating IgM. IgM almost always

circulates as a pentamer (19S). Therefore, when one

develops a monoclonal proliferation of cells producing IgM,

the increased concentration of large proteins in the blood

disturbs the normal circulation hemodynamics, resulting in

the hyperviscosity syndrome. This causes a variety of

neurologic complaints, cardiac insufficiency, and vascular

insufficiency throughout the body.

Waldenström's Macroglobulinemia

Monoclonal Gammopathy Of Undetermined Significance

In older textbooks, the term for this section would

have been "benign monoclonal gammopathies." 　

By this term, he referred to individuals who have a

monoclonal component demonstrated in the serum, but

who lack other key features for diagnosing a malignant

monoclonal gammopathy. These patients are not anemic,

they do not have lytic lesions, and they do not have

elevated serum calcium or serum enzymes.

A variety of B-cell neoplasms have been associated

with monoclonal gammopathies. In fact, the

majority of these patients have a monoclonal

gammopathy in either their serum or their urine

when high-resolution electrophoresis and

immunofixation are combined to study these

samples. Monoclonal gammopathies also have been

demonstrated in patients with Burkitt's lymphoma

and B-cell ALL.

B-Cell Neoplasms

About 4% patients with plasma cell proliferation

will have amyloid deposition in their tissues. There

are two major biochemical types of amyloid.

One consists of an immunoglobulin light chain and

is termed AL.

The second is composed of protein A and is termed

AA.

Amyloidosis