Chapter 13: Diseases of White Blood Cells, Lymph Nodes, and Spleen

A bnormalities in white blood cells (WBCs) are nearly always quantitative (eg, too many or too few WBCs). These disorders may be neoplastic, as found in leukemia, or nonneoplastic. A qualitative or functional disorder of WBCs may accompany the quantitative disorder. Qualitative defects in WBC function with a normal WBC count occur, but they are uncommon. The approach to diagnosis of WBC disorders is shown in Figure 13–1.

Description and Diagnosis

A low WBC count can occur because of a decreased number of lymphocytes, granulocytes, or both. A number of the immunodeficiency diseases are associated with a lymphocytopenia (see Chapter 3). Granulocytopenia primarily reflects a reduction in the number of neutrophils (neutropenia) in the peripheral blood. When the number of neutrophils decreases below about 1000 neutrophils/μL, the neutropenic patient becomes susceptible to infections. These illnesses range from mild to severe, depending on the type of organism and the effectiveness of the antibiotics used to treat it. A classification of granulocytopenic disorders follows.

Defects in the production of granulocytes may be caused by:

• Diseases associated with marrow failure, such as aplastic anemia.

• Diseases in which the marrow is infiltrated by leukemic cells or by metastatic cancer cells originating from another site; the decreased neutrophil production in this setting is typically associated with defects in the production of other blood cells as well.

• Suppression of granulocyte production by exposure to certain drugs; the list of drugs that can produce neutropenia is extensive; noteworthy examples are chemotherapeutic agents used in cancer treatment and certain nonsteroidal anti-inflammatory drugs (NSAIDs).

• Vitamin B₁₂ or folate deficiency; these disorders produce a megaloblastic anemia and defective DNA synthesis in granulocyte precursors.

• Suppression of granulocyte production by neoplastic cells, for example, large granular lymphocytic leukemia.

Accelerated removal of granulocytes may be caused by:

• Immunologically mediated injury to neutrophils following exposure to drugs, with the injury occurring from an immune response on the neutrophil surface.

• Immunologically mediated injury to neutrophils as part of an autoimmune disorder; for example, Felty syndrome is a variant of rheumatoid arthritis with neutropenia, splenomegaly, leg ulcers, and the joint lesions found in rheumatoid arthritis; the neutropenia can dominate the clinical course in patients with Felty syndrome.

• Immunologically mediated injury to neutrophils that is idiopathic and not associated with any identifiable abnormality.

• Excessive destruction of granulocytes from splenic sequestration of the neutrophils in an enlarged spleen or from overwhelming infection.

Description and Diagnosis

An elevated peripheral WBC count is commonly found in patients with infections and other inflammatory states, such as those associated with autoimmune disorders.

Lymphocytes

Patients can develop a lymphocytosis in a variety of different conditions such as tuberculosis, acute bowel infections, and infectious mononucleosis and other viral infections.

Eosinophils

An increase in circulating eosinophils is most commonly found in patients with allergic disorders and those with asthma. An increase in circulating eosinophils is also found in patients with certain parasitic infections and in patients with dermatologic disorders such as eczema. Increases in eosinophils can also be caused by some drugs and some autoimmune disorders. Finally, increases in eosinophils can be seen in certain neoplastic conditions such as Hodgkin lymphoma and T-cell lymphomas.

Monocytes

The peripheral monocyte count is increased in a number of situations where the lymphocyte count is also increased, such as tuberculosis. Rheumatoid arthritis, systemic lupus erythematosus, and other connective tissue diseases also may be associated with a monocytosis.

Neutrophils

A mild increase in circulating neutrophils can occur without disease after strenuous exercise, during menstruation, and in the course of pregnancy. An increased neutrophil count is clinically significant when it is indicative of a bacterial infection, a neoplastic disorder, ischemia, an autoimmune disorder, or an effect of certain drugs, such as corticosteroids or epinephrine. The most frequently identified immature neutrophil in the blood when there is an increased WBC count is the neutrophilic band cell. The percentage of WBCs represented by band cells or more immature neutrophil precursors is a commonly used indicator of infection. However, band counts are poorly reproducible among medical technologists, so the current trend is to not report band counts. Other less mature neutrophil precursors can be seen in infections and other conditions where the bone marrow is attempting to produce granulocytes rapidly.

WBC neoplasms frequently involve the peripheral blood, and can result in leukocytosis. White cell neoplasms are broadly divided into 2 large categories, lymphoid (the lymphocyte lineage) and myeloid (the lineage including granulocytes, monocytes, megakaryocytes, and erythroid cells). Lymphoid disorders include acute precursor lymphoblastic leukemias (ALL) and mature B-, T-, and NK-cell neoplasms. Myeloid disorders include acute myeloid leukemias, myeloproliferative neoplasms, and myelodysplastic syndromes.

Description and Diagnosis

The lymphoid malignancies are caused by neoplastic transformation of lymphocytes or their precursors. Lymphoid cells can be found in the lymph nodes, blood, bone marrow, spleen, and extranodal sites such as the skin, mucosae, and respiratory and gastrointestinal tracts. Lymphoid neoplasms can occur at any of these sites. Neoplasms that primarily involve the bone marrow and peripheral blood are referred to as leukemias, and those involving tissue sites are called lymphomas. However, many lymphoid malignancies can involve both tissues and the blood/bone marrow, so the leukemia/lymphoma distinction is somewhat arbitrary. The World Health Organization (WHO) classification system for lymphoid malignancies is shown in Table 13–1.

Lymphoid leukemias can correspond to precursor B or T cells or mature lymphoid cells. Precursor lymphoid malignances are also called lymphoblastic leukemias/lymphomas. Relatively common B- and T-cell malignancies that frequently present in a leukemic phase include chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma, hairy cell leukemia, mantle cell lymphoma, Burkitt lymphoma/leukemia, T-cell prolymphocytic leukemia, T-cell large granular lymphocytic leukemia, and Sézary syndrome. Lymphoid leukemias generally present with elevated white counts (specifically lymphocytosis), and depending on the degree of bone marrow involvement, there can be decreased numbers of normal white cells, red cells, and/or platelets. Processes that involve the marrow extensively can result in the presence of myeloid and erythroid precursor cells in the peripheral blood. Leukemias are diagnosed by examination of the peripheral blood smear and bone marrow aspirates and biopsies. Additional studies such as immunophenotyping by flow cytometry, molecular diagnostic techniques, and cytogenetics are frequently used to establish a diagnosis.

When lymphoid malignancies are mostly tissue-based, they are referred to as lymphomas. Lymphomas are monoclonal, neoplastic proliferations of B, T, or NK cells. Most lymphomas are malignancies of mature lymphocytes, but precursor lymphocytic malignances can involve tissues, and thus be classified as lymphomas. Lymphomas are divided into 2 major groups, Hodgkin lymphoma and a much larger variety of lymphomas known generically as non-Hodgkin lymphomas. The patient with lymphoma often presents with an isolated, enlarged superficial lymph node, which may be discovered accidentally on physical exam. Alternatively, the patient may have generalized lymphadenopathy. If the enlarged lymph node develops in a site where it can produce signs and symptoms, it is more likely to be discovered early in the course of disease. An example is the enlargement of lymph nodes in the mediastinum, which can impair blood flow through the large vessels in the chest and produce symptoms on that basis. In some cases, organ involvement may be the first manifestation of a lymphoma. Non-Hodgkin lymphomas, for example, may become symptomatic when there is cellular proliferation in the orbit, the gastrointestinal tract, or the skin. Involvement of the bone marrow and peripheral blood also may be an initial indicator of the presence of a lymphoma.

Lymph node biopsy is the preferred method for diagnosis of lymphoma, since it allows the pathologist to determine the overall tissue architecture and get a large sample of the cells present. Because the lymphoma may not be distributed evenly in all lymph nodes, it may be necessary to biopsy several lymph nodes to establish the diagnosis. In recent years, both fine needle aspiration and biopsy have been used more commonly to make diagnoses of lymphoma. Although fine needle aspiration does not allow optimal evaluation of tissue architecture, diagnostic procedures such as flow cytometry and/or molecular techniques can be used to render a diagnosis on minimal amounts of material.

Principal differentiating factors between Hodgkin and non-Hodgkin lymphomas are:

• Hodgkin lymphoma:

  • (a) Proliferation of cells is typically localized to a single group of nodes such as the cervical or mediastinal nodes.

  • (b) Proliferating cells spread by contiguity.

  • (c) Mesenteric lymph nodes are rarely involved.

• Non-Hodgkin lymphomas:

  • (a) Frequent involvement of multiple groups of nodes.

  • (b) Proliferating cells spread widely and noncontiguously.

  • (c) Mesenteric lymph nodes are commonly involved.

The Hodgkin and non-Hodgkin lymphomas are classified into clinical stages based on the distribution of the disease. These stages, with increased clinical severity associated with higher stage numbers, are as follows:

• Stage I—involvement of 1 group of lymph nodes or 2 contiguous lymph node clusters on the same side of the diaphragm.

• Stage II—involvement of 2 or more noncontiguous lymph node groups on the same side of the diaphragm.

• Stage III—lymph node involvement above and below the diaphragm; if there is involvement of the spleen, the lymphoma is classified as III(s); and if there is visceral involvement by direct extension, it is known as stage III(e).

• Stage IV—widespread disease, often involving the liver, bone marrow, lungs, bones, and skin.

In addition to the above staging scheme, the designation “B” is added for patients who have constitutional symptoms such as fever, night sweats, and weight loss. For example, a patient with involvement of 2 groups of lymph nodes on the same side of the diaphragm with fevers and night sweats would be considered stage IIB. In general, the presence of these “B symptoms” portends a more advanced stage of disease with worse prognosis. In addition, the designation “E” is used to designate lymphomas involving extranodal sites only (eg, the gastrointestinal tract).

Lymphoma

Historically the diagnosis of Hodgkin and non-Hodgkin lymphoma was primarily based on the histological appearance of the lymph nodes. For Hodgkin lymphoma, the Rye classification system was used for decades and has now been incorporated with relatively few changes into the current WHO classification system for hematologic malignancies. Classification of non-Hodgkin lymphomas has been more problematic. Non-Hodgkin lymphomas were organized in the Rappaport classification in 1966, the Lukes–Collins classification in 1973-1974, and in 1982 they were reclassified according to the Working Formulation of Clinical Usage by an international panel of experts.

By the early 1990s, significant progress was made in understanding the biology of lymphomas, so newer classification systems were developed based on typing lymphomas with antibodies specific for cytoplasmic and cell surface proteins (immunohistochemistry and flow cytometry) and by detecting specific molecular lesions. In 1994, the REAL classification was introduced by the International Lymphoma Study Group. The goal of the new classification was to integrate morphological, immunologic, and genetic information to better define the disease entities. The REAL classification system was modified somewhat to form the basis for the current (2008) WHO classification system (Table 13–1).

The WHO classification system, like the REAL classification system preceding it, attempts to classify non-Hodgkin lymphomas according to the normal cell equivalent of the neoplastic cells. First, neoplastic cells are classified based on whether they are of B-cell or T-cell/NK-cell origin. Next, the cells are classified by the stage of differentiation to which they correspond. Most B- and T-cell neoplasms correspond to mature B and T cells.

In the end, lymphoma classification is determined by the architectural features observed under the microscope (eg, follicular vs diffuse growth pattern and the microscopic appearance of the malignant cells), the spectrum of proteins expressed on the surfaces and in the cytoplasm of the malignant cells (eg, T- or B-cell markers and proteins not expressed in normal lymphocytes), the presence of clonal rearrangements of the immunoglobulin or T-cell receptor genes, and, in some cases, the presence of specific genetic lesions in the malignant cells. The techniques used for lymphoma diagnosis include light microscopy, immunohistochemistry, flow cytometry, and molecular techniques including cytogenetics, fluorescence in situ hybridization (FISH), polymerase chain reaction (PCR), and newer techniques such as microarrays.

Since it is beyond the scope of this chapter to discuss all the lymphoid malignancies in detail, the more common disorders have been selected for inclusion.

Precursor B- and T-cell Neoplasms

Neoplasms of immature B and T cells most commonly present as leukemias, with extensive blood and bone marrow involvement, but they can also involve the lymphoid tissues as lymphomas. For example, precursor T-cell leukemia/lymphoma often presents with a mediastinal mass and may not demonstrate blood or bone marrow involvement. ALL accounts for almost one third of all childhood cancers and represents 75% of all pediatric leukemias. The median age at diagnosis is 10 years with a slight male predominance of 1.4:1. Pediatric leukemias are almost always (80%-85%) of a precursor B-cell lineage, with the remainder being T-cell lineage.

Diagnosis

• Morphology—Morphologically, the involved tissues show monomorphic collections of medium-sized cells with fine chromatin, high nuclear:cytoplasmic ratios, and inconspicuous nucleoli.

• Immunophenotyping—Depending on lineage, the cells will express B- or T-cell surface proteins. Both B- and T-cell precursor cells contain the enzyme terminal deoxynucleotidyl transferase.

• Cytogenetics—There are a number of recurrent chromosomal translocations associated with ALL. Hyperdiploidy with 50 or more chromosomes is a favorable prognostic finding. The presence of the Philadelphia chromosome, t(9;22)(q43;q11), is an adverse prognostic finding.

Description

CLL is the most common of the non-Hodgkin lymphomas. The median age at diagnosis is 70 years with a slight male predominance of 1.7:1. The neoplastic cells in CLL are mature B cells. CLL is an indolent disease with a highly variable life expectancy. Transformation to aggressive disease occurs in 5% to 10% of cases at any time during the course of the illness, and is usually a terminal event.

Diagnosis

• Morphology—The lymphocytes in CLL are usually small and well differentiated. They are sometimes difficult to distinguish from normal lymphocytes, but they can be identified by their somewhat larger size, coarsely clumped chromatin, and tendency to break apart on peripheral blood smears, forming “smudge cells.” CLL can transform into a high-grade B-cell lymphoma known as Richter syndrome in approximately 3% of B-cell CLL cases. Another type of transformation is to the prolymphocytoid form, where patients can have a very high white count of characteristic prolymphocytes with prominent nucleoli.

• Immunophenotyping—The CLL tumor cells express low levels of monoclonal surface IgM and IgD in the majority of cases, surface IgM only in approximately 25% of the cases, and surface IgD, other immunoglobulin isotypes, or no surface immunoglobulin in a small percentage of cases. A characteristic finding in CLL is expression of CD5, which is normally a pan-T-cell antigen, but is expressed on a minor normal subset of B cells. CLL cells also express the B-cell antigens CD19, CD20 (low level), and CD23. Immunophenotyping can also be used for prognosis: high-level expression of CD38 and ZAP-70 is associated with worse prognosis.

• Cytogenetics—Chromosomal abnormalities in CLL have prognostic significance. Deletions of 11q and 17p are associated with significantly shorter survival. Deletion of 13q is associated with better prognosis.

• Molecular genetics—As with all B-cell lymphomas, the cells of CLL have clonally rearranged immunoglobulin genes. CLL with hypermutated immunoglobulin gene regions (compared with the baseline unmutated sequences) has a better prognosis. Unmutated immunoglobulin genes are associated with worse prognosis.

Hairy Cell Leukemia

Description

Hairy cell leukemia is an uncommon form of non-Hodgkin lymphoma. This disease generally occurs in men with a median age at diagnosis of 50 years. The male to female ratio is approximately 4:1. The clinical manifestations are primarily the result of infiltration of the tumor cells into the bone marrow, liver, and spleen. A significant clinical finding on physical examination is the often massive splenomegaly. The liver is also enlarged, but to a much lesser degree than the spleen. Marrow failure is common in this disease, resulting in pancytopenia and its associated complications. Patients generally present with splenomegaly, leukopenia with a relative decrease in monocytes, and an inaspirable bone marrow.

Diagnosis

• Morphology— The diagnosis of hairy cell leukemia is supported by the identification of lymphocytes with bean-shaped nuclei and fairly abundant gray cytoplasm, giving the cells a somewhat monocytic appearance. Fine cytoplasmic projections that have a hair-like appearance on Wright–Giemsa-stained smears give this entity its name.

• Cytochemistry—The cells in hairy cell leukemia stain positively for acid phosphatase that is partially or completely resistant to removal on the addition of tartrate. This is known as TRAP, for tartrate-resistant acid phosphatase. TRAP-positive lymphocytes with fine cytoplasmic projections are highly consistent with a diagnosis of hairy cell leukemia.

• Immunophenotyping—The hairy cells have a B-cell phenotype, with monoclonal surface immunoglobulin, CD19 (increased), and CD20 (increased). Antigens that are relatively specific for hairy cell leukemia include the interleukin 2 receptor alpha, CD25, as well as surface CD11c and CD103. Immunohistochemistry performed on bone marrow biopsies or spleen can be used to detect DBA44, which is relatively selective, although not specific, for hairy cell leukemia. These results are all consistent with the identification of hairy cell leukemia as a B-cell disorder.

• Molecular genetics—The neoplastic B cells of hairy cell leukemia have clonally rearranged immunoglobulin genes. Recently most hairy cell leukemias were found to have a mutation of the BRAF gene (V600E) that was previously found in melanoma. This mutation is relatively specific for hairy cell leukemia and does not appear to affect disease prognosis.

Plasma Cell Dyscrasias

The plasma cell dyscrasias are disorders in which there is an expansion of a single clone of immunoglobulin-secreting cells. This results in the appearance of high levels of complete or incomplete immunoglobulin molecules in the serum or urine. The monoclonal immunoglobulin in the serum is known as an M-component because it is found in the prototype disorder in this group of diseases, multiple myeloma. Incomplete immunoglobulins containing only light chains or only heavy chains may be produced in certain plasma cell dyscrasias. The free light chains, which are known as Bence-Jones proteins, may be excreted into the urine. The 5 disorders included in this grouping of plasma cell dyscrasias are plasma cell myeloma, Waldenström macroglobulinemia, heavy chain disease, primary amyloidosis, and monoclonal gammopathy of unknown significance (MGUS). Amyloidosis is discussed in Chapter 3, and the other entities are described as follows.

Plasma Cell Myeloma

Description

Plasma cell myeloma, also known as multiple myeloma, is a disorder resulting from proliferation of a single plasma cell clone that produces a monoclonal immunoglobulin. The median age for presentation is 62 years. The most frequent presenting symptom is bone pain resulting from osteolytic lesions produced by clusters of plasma cells infiltrating the bone. The bones most often affected are the skull, the ribs, the vertebrae, and the long bones of the extremities. Because patients with multiple myeloma are often anemic, fatigue and weakness are common presenting symptoms. Patients may also experience recurrent bacterial infections as a result of the leukopenia that occurs later in the disease. In addition, the passage of free light chains into the urine may result in “myeloma kidney” and lead to renal failure. The diagnosis of myeloma depends on the presence of a monoclonal protein in the serum or urine, and then the type of myeloma is further classified based on the severity of the disease (Table 13–2). A skeletal survey is included in the initial workup of myeloma to assess the extent of bone involvement.

Diagnosis

• Morphology—The diagnosis of plasma cell neoplasm is made when increased numbers of plasma cells are observed in a bone marrow or tissue biopsy. In the bone marrow, plasma cell numbers will be increased, and they form small clusters to extensive sheets in bone marrow biopsies. Solitary tissue lesions, often involving bone, may also show sheets of abnormal plasma cells and are classified as plasmacytomas. Abnormal plasma cells are rarely seen in the peripheral blood, and “plasma cell leukemia” is considered an end-stage presentation of this disorder.

• Immunophenotyping—Abnormal plasma cells can be detected by flow cytometry based on abnormal loss of CD19 and CD45, expression of CD38 and CD138, and monoclonal immunoglobulin light chain in the cytoplasm. The abnormal cells may express CD56, which is absent on normal plasma cells. In tissue sections, the abnormal plasma cells are recognized by expression of CD138 and monoclonal cytoplasmic immunoglobulin light chain expression.

• Cytogenetics—Chromosomal abnormalities in myeloma have prognostic significance. Most commonly FISH is used to identify specific abnormalities. For FISH, fluorescent DNA probes for the genes of interest are used to localize these genes in chromosome preparations or in cell nuclei. These probes can determine if 2 separate genes are brought together in a translocation or if a gene is broken apart by a translocation. It is helpful to use some kind of enrichment technique, such as magnetic beads coated with antibodies that plasma cells express (eg, CD138), to obtain enough plasma cells to study. Favorable risk cytogenetic abnormalities include hyperdiploidy, t(11;14) or t(6;14). Poor risk cytogenetic abnormalities include deletion of chromosome 13, t(4;14), t(14;16), t(14;20), deletion of 17p13, and hypodiploidy.

• Molecular genetics—Plasma cell neoplasms have clonal rearrangements of their immunoglobulin genes.

• Protein electrophoresis—The evaluation of a patient for multiple myeloma begins with protein electrophoresis of serum and urine to identify any monoclonal proteins (see Chapter 2 for protein electrophoresis and immunofixation). An M-component on an electrophoretic gel is a dense band of protein that is not usually present. It most often migrates in the gamma region of the gel, but occasionally appears in the beta or alpha-2 region. To increase the likelihood of M-component detection in the urine, the samples evaluated for M-components must be concentrated prior to electrophoresis. Confirmation that a band identified on serum or urine protein electrophoresis represents an M-component involves further analysis by immunofixation electrophoresis (see Chapter 2) or, much less frequently now, by immunoelectrophoresis. Both of these tests permit identification of the specific heavy chain and light chain of the M-component, if both are present. It is also necessary to quantify serum immunoglobulins to determine if the concentration of the M-component is greater than 35 g/L.

• Other chemistry tests—Beta-2 microglobulin is the light chain of a class 1 major histocompatibility complex protein, and is present on the surface of all nucleated cells. Increased levels of the unbound beta-2 microglobulin in the plasma are found in multiple myeloma and are considered a reflection of tumor burden. Other tests used to evaluate myeloma include measurement of serum calcium and evaluation of renal function.

Waldenström Macroglobulinemia

Description

Waldenström macroglobulinemia is the clinical syndrome associated with lymphoplasmacytic lymphoma in the WHO classification. There is a diffuse infiltration of the bone marrow by small lymphocytes and plasma cells that synthesize an IgM immunoglobulin, which is referred to as a macroglobulin. It is similar to plasma cell myeloma in that both have an M-component. However, the M-component in Waldenström macroglobulinemia is always an IgM molecule, and unlike the relatively rare IgM myeloma patient, individuals with Waldenström macroglobulinemia do not have lytic bone lesions. The mean age for presentation is 63 years, with a slight male predominance. Patients frequently present with fatigue, weight loss, weakness, and bleeding from anemia and thrombocytopenia. When present in sufficient concentration, the large circulating IgM protein produces a hyperviscosity syndrome in the plasma and tissue deposition of IgM. Most patients with Waldenström macroglobulinemia have an elevated serum viscosity, but only 15% to 20% are symptomatic. The most common symptoms associated with slow blood flow from hyperviscosity are blurred vision, mucosal bleeding, dizziness, and, on funduscopic examination of the eye, papilledema, hemorrhage, and distention of the retinal veins.

Diagnosis

• Morphology—The pathological correlate of Waldenström macroglobulinemia is lymphoplasmacytic lymphoma. The abnormal cells are small mature-appearing lymphocytes, some of which may resemble small plasma cells. The cells can be present in tissue biopsies, peripheral blood, or bone marrow.

• Immunophenotyping—The abnormal cells express the B cell markers CD19 and CD20 without coexpression of CD5 or CD10. The cells will have surface expression of monoclonal immunoglobulin. The abnormal cells may express plasma cell antigens such as CD38 or CD138.

• Protein electrophoresis—The diagnosis of Waldenström macroglobulinemia requires demonstration of an IgM serum protein concentration greater than 30 g/L. As with multiple myeloma, Waldenström macroglobulinemia must be differentiated from an IgM MGUS.

• Molecular genetics—Recently a mutation in the MYD88 gene (L265P) has been found to be specifically associated with Waldenström macroglobulinemia.

Heavy Chain Disease

Description

The heavy chain diseases are a group of lymphoproliferative disorders in which there is production of monoclonal immunoglobulins with only heavy chains. Each type of heavy chain disease is named for the abnormal heavy chain produced, resulting in:

• Alpha chain disease—a high serum concentration of the heavy chain present in IgA

• Gamma chain disease—a high serum concentration of the heavy chain present in IgG

• Mu chain disease—a high serum concentration of the heavy chain present in IgM

All the heavy chain diseases are rare, with alpha chain disease having the highest incidence of the related disorders. In all 3 disorders, the monoclonal heavy chain is defective with internal deletions of most of the variable region of the protein and some portion of the first constant region domain. Common clinical findings in patients with heavy chain disease are splenomegaly, hepatomegaly, and lymphadenopathy. Almost all cases of mu chain disease have been associated with CLL. Gamma chain disease has been found in the presence of a variety of autoimmune disorders and in lymphoplasmacytic lymphoma. Alpha chain disease is associated with extranodal marginal zone lymphoma of the MALT type, which usually involves the gastrointestinal tract.

Diagnosis

The diagnosis of heavy chain disease is made primarily by demonstration of a monoclonal heavy chain by protein electrophoresis of serum, concentrated urine, or both. The diagnosis of heavy chain disease should prompt an investigation into the presence of lymphoma if that diagnosis has not already been made.

Monoclonal Gammopathies of Unknown Significance

Description

Patients with MGUS are asymptomatic but have a monoclonal protein in their serum and/or urine. There is an increasing incidence of MGUS with aging. Because the incidence of malignant monoclonal gammopathies also increases with age, it is essential to differentiate patients who have MGUS from those who have plasma cell myeloma or Waldenström macroglobulinemia. Most patients with MGUS remain clinically stable without therapy for many years. However, as many as 15% to 20% develop myeloma, macroglobulinemia, amyloidosis, or lymphoma. Indolent myeloma and smoldering myeloma, disorders with many features of multiple myeloma and Waldenström macroglobulinemia that do not meet the criteria for diagnosis, can be differentiated from MGUS because MGUS has a lower amount of immunoglobulin in the serum and a lower percentage of plasma cells in the bone marrow.

Diagnosis

MGUS is diagnosed by the presence of a monoclonal serum or urine immunoglobulin at a concentration less than that required for a myeloma diagnosis, less than 10% abnormal plasma cells in the bone marrow, no lytic bone lesions, and no symptoms suggestive of multiple myeloma.

Hodgkin Lymphoma

Description and Diagnosis

Hodgkin lymphoma is distinguished from non-Hodgkin lymphoma by the presence of a neoplastic giant cell known as a Reed–Sternberg cell in the lymph node. For many years the lineage of the Reed–Sternberg cell was controversial, but the best information now indicates that the Reed–Sternberg cell is an abnormal malignant B cell. Hodgkin disease is a common form of malignancy in young adults with a second peak incidence in older individuals. Unlike the multiple classification schemes for non-Hodgkin lymphomas, a classification of Hodgkin disease known as the Rye classification was accepted for decades. This classification system has now been incorporated with minor changes into the WHO classification system for hematologic malignancies. Hodgkin lymphoma is divided into 2 broad categories: classical Hodgkin lymphoma and nodular lymphocyte-predominant Hodgkin lymphoma. Classical Hodgkin lymphoma is characterized by infrequent Reed–Sternberg cells in a background of normal lymphocytes, plasma cells, eosinophils, and granulocytes. The Reed–Sternberg cells lack expression of the pan-hematopoietic marker CD45; they occasionally express the B-cell marker CD20, and they characteristically express CD30 and CD15. The different subtypes of classical Hodgkin lymphoma in the WHO classification are characterized primarily by differences in tissue architecture and the composition of the cellular background.

Nodular lymphocyte-predominant Hodgkin lymphoma also shows scattered large abnormal cells, but these do not have the appearance of Reed–Sternberg cells. The abnormal cells in nodular lymphocyte-predominant Hodgkin lymphoma have convoluted nuclei, leading to the term “popcorn cells.” These abnormal cells express the pan-hematopoietic marker CD45 and the B-cell marker CD20; they variably express CD30 and do not express CD15. The abnormal cells are frequently ringed by normal T cells. Nodular lymphocyte-predominant Hodgkin lymphoma is best thought of as a low-grade B-cell lymphoma.

Acute Myeloid Leukemias

Acute leukemias are hematologic malignancies that primarily involve the peripheral blood and bone marrow. An acute leukemia is a neoplasm of a hematopoietic stem cell that has lost its capacity to differentiate and regulate its own proliferation. The outcome of the expansion of the leukemic clone is an accumulation of poorly differentiated WBC precursors known as blasts in the bone marrow. These limit the production of normal blood cells. The blasts commonly appear in the peripheral blood and permit identification of an acute leukemia from review of the peripheral blood smear. A diagnosis of acute leukemia requires that 20% or more of the bone marrow cells be blasts. These disorders are usually rapidly progressive, and patients can die within days to weeks without therapeutic intervention. In the WHO classification, leukemias are not considered an independent group of diseases. Instead, they are classified according to their cell of origin. Acute leukemias of lymphoid cells are included in the B- and T-cell malignancy classification scheme. In this section, we will consider the acute myeloid leukemias, which are malignancies of myeloid stem and precursor cells.

Leukemias cannot generally be diagnosed by morphology alone. In particular, it is frequently not possible to distinguish leukemias of myeloid lineage from leukemias of B- or T-cell precursors. Special cytochemical stains can sometimes help identify the lineage of the leukemic cells, but definitive classification is best done by immunophenotyping using flow cytometry. It is also important to perform cytogenetic and/or molecular analysis of leukemias, to obtain prognostic information and, in some cases, information that can be used to design specific therapy. The description and diagnosis for several acute leukemias are presented in the sections that follow.

A uniform classification for the acute leukemias was developed in 1976 by the French–American–British (FAB) cooperative group. The classification from the FAB cooperative group ultimately divided AML into 7 types, M1 to M7. These types were based primarily on the morphology of the leukemic blasts and in some cases on cytochemical staining. In 1990, the National Cancer Institute established guidelines for an M0 type of AML that is not within the M1 to M7 classification. The distinction between AML and the myelodysplastic syndromes was clarified at that time (see the section “Myelodysplastic Syndromes”). As more has been learned about the molecular pathophysiology of AML, it has become clear that the FAB categories do not correspond to distinct biological entities. For example, the translocation t(8;21) can be found in several different FAB types. The one exception is FAB type M3, acute promyelocytic leukemia. This leukemia reproducibly has a translocation t(15;17), and is unique among the myeloid leukemias in its response to treatment by all-trans retinoic acid or arsenic trioxide.

The 2008 WHO classification system recognizes some of the drawbacks of the FAB system. New features of the WHO system include defining specific leukemias by their molecular pathology for those with recurrent chromosomal abnormalities, and creating categories for leukemias evolving from previous myelodysplastic syndromes and from patients treated with leukemogenic chemotherapy for prior malignancies that do not fit neatly into the FAB categories (see Table 13–3). For the remaining myeloid leukemias (“not otherwise specified”), classification is similar to the FAB system (see Table 13–4).

Leukemias With Recurrent Genetic Abnormalities

Certain common chromosomal translocations are found in acute myeloid leukemia. These translocations usually result in the generation of an abnormal transcription factor that alters gene expression, leading to leukemia. The most common recurrent translocation is the t(8;21)(q22;q22) involving the genes RUNX1–RUNX1T1. It is seen in several FAB types of AML and is associated with a relatively good prognosis. The inv(16) translocation involves the genes CBFB–MYH11 and is associated with a type of myelomonocytic leukemia that has increased eosinophils in the bone marrow (FAB type AML M4-Eo). It is also associated with a relatively good prognosis. The t(15;17) translocation involves the genes PML–RARA and is uniquely associated with acute promyelocytic leukemia (FAB type M3). This translocation results in an abnormal form of the retinoic acid receptor α (RARA). Interestingly, acute promyelocytic leukemia can be treated with all-trans retinoic acid in addition to standard leukemia chemotherapy, and many patients have a good outcome. The all-trans retinoic acid presumably interacts with the abnormal product of the t(15;17) fusion gene and interferes with its leukemogenic function. This was the first acute leukemia therapy described that was directed at the molecular pathology of the leukemia. Another recurrent chromosomal abnormality associated with AML is the t(9;11) involving the genes MLLT3–MLL, the latter of which is at chromosome 11q23. In addition to MLLT3, MLL forms fusion genes with many different partner genes. It is found more commonly in pediatric AML and is associated with a somewhat worse clinical outcome. Rarer translocations that are defined entities in the WHO classification include t(6;9)/DEK–NUP214, inv(3)/RPN1–EVI1, and t(1;22)/RBM15–MKL1.

Secondary Acute Myeloid Leukemia

Unlike the leukemias with recurrent chromosomal abnormalities, which are thought to represent de novo events, there is a group of leukemias that evolve out of previously existing conditions. One set consists of the leukemias that develop from patients with stem cell disorders such as the myelodysplastic syndromes (see below). These leukemias are associated with morphological abnormalities in all hematopoietic lineages. The other secondary leukemias develop in patients who have had previous chemotherapy for other malignancies. These leukemias occur in patients who were treated with alkylating agents such as cyclophosphamide or nitrogen mustard or with topoisomerase inhibitors such as the epipodophyllotoxins or anthracyclines. Both sets of leukemias are associated with complex cytogenetic abnormalities and have poor prognoses.

Other Acute Myeloid Leukemias

Leukemias that do not have characteristic cytogenetic abnormalities or documented previous stem cell disorders or therapy are characterized by their putative lineage as determined by immunophenotyping, morphology, and cytochemical staining. Their classification is most similar to the FAB system used prior to the WHO classification. The diagnostic criteria for these leukemias are shown in Table 13–4.

Biphenotypic and Mixed Lineage Leukemias

There is a subset of acute leukemias that express both myeloid and lymphoid markers at the same time on the same blasts. These are called mixed lineage leukemias. These leukemias may reflect a lack of marker specificity or aberrant gene expression by a malignant hematopoietic stem cell. Biphenotypic leukemias have separate subpopulations of leukemic blasts with different immunophenotypes (eg, myeloid on 1 set and lymphoid on another). Both types of leukemias generally have a relatively poor prognosis.

Diagnostic Techniques for AML

• Cytochemistry—Two cytochemical stains are widely used in the diagnostic evaluation of an acute leukemia. These are myeloperoxidase (MPO) and nonspecific esterase (NSE). MPO identifies cells of myeloid lineage, which usually stain intensely positive for MPO. Monoblasts and promonocytes, which appear in acute myelomonocytic leukemia, can also react with MPO. NSE is confined mostly to cells of monocytic lineage, which predominate in acute monoblastic/monocytic leukemia.

• Immunophenotyping—With the development of monoclonal antibodies that can be fluorochrome-conjugated to bind to and identify cell antigens, flow cytometry has become a useful tool in distinguishing AML from ALL, and identifying the individual subtypes of AML. Immunophenotyping is particularly important in the identification of blasts that show no morphological features to indicate their lineage, as found in the minimally differentiated subtype of AML. Markers such as CD14 and CD64 can be useful in identification of monocytic cells in AML. The detection of hemoglobin or glycophorin A aids in the diagnosis of erythroleukemia. Identification of platelet glycoprotein antigens supports a diagnosis of acute megakaryoblastic leukemia.

• Cytogenetics and FISH—As described above, certain types of AML are defined by specific chromosomal rearrangements. Traditionally, chromosomal rearrangements are detected by cytogenetic studies, in which the chromosomes of dividing leukemic blasts are stained and examined under the microscope, which allows the different chromosomes to be identified, and where abnormal chromosome rearrangements can be detected. To look for specific gene rearrangements, FISH is used, which is the fastest and most sensitive method for detecting the specific rearrangements in leukemias with recurrent genetic abnormalities.

• Molecular genetics—Molecular genetic tests are also used to provide diagnostic and/or prognostic information not available from morphological analysis. For example, PCR gene amplification (in addition to FISH) can be used to detect the recurrent cytogenetic translocations of AML. Molecular analysis can also be used to detect mutations in specific genes such as FLT3, NPM1, and CEBPA, which frequently occur in AML with otherwise normal cytogenetics. Finally, PCR to detect translocation-specific fusion RNAs can sensitively detect residual leukemic cells after chemotherapy or transplantation and thereby permit earlier intervention.

Laboratory Approaches for Determination of AML Prognosis

Acute myeloid leukemia is currently treated initially with one of a small number of chemotherapy regimens, all of which are quite toxic to the bone marrow and other organs. By studying large numbers of patients with AML, it has become clear that certain types of AML tend to respond well to standard chemotherapy, whereas others do poorly and require more intensive chemotherapy regimens and/or stem cell transplantation if a patient has a chance to be cured. This research has shown that cytogenetic and molecular abnormalities correlate well with prognosis, and thus the clinical laboratory has a critical role to play in determining the therapy for patients with AML: the goal is to identify those patients who need more aggressive treatment at the time of their diagnosis while sparing those with a better prognosis exposure to unnecessary and possibly life-threatening therapy.

The traditional way of determining AML prognosis has been to use cytogenetic studies to place patients into favorable, unfavorable, or intermediate risk groups (see Table 13–5). Favorable risk cytogenetics include AML with t(8;21), inv(16), or t(15;17). Unfavorable risk cytogenetics include AML lacking more than 1 chromosome, inv(3), MLL rearrangements, and AML with multiple cytogenetic abnormalities. Those meeting neither favorable risk nor unfavorable risk criteria are considered intermediate risk, including AML with no cytogenetic abnormalities.

Further information about AML prognosis has come from studying individual genes found to have an impact on a patient's likelihood of cure with standard chemotherapy. One of the most important genes for prognosis is the FLT3 gene. When this gene is mutated in AML cells, it puts a patient into an unfavorable risk category, even if the AML has other more favorable risk characteristics. In contrast, mutation of the NPM1 gene confers more favorable risk if there is no FLT3 mutation. Similarly, if both copies of the CEBPA gene are mutated, the patient is considered favorable risk, again in the absence of a FLT3 mutation. Mutation of the KIT gene confers a poor prognosis on the t(8;12) and inv(16) AMLs, which ordinarily have a good prognosis. Currently many more genes are being recognized as having an impact on AML prognosis, and genetic analysis is likely to replace cytogenetics for determining AML prognosis. Next-generation sequencing technologies are rapidly evolving and will allow numerous genes, or even the entire genome, of AML cells to be determined, which will improve the ability to determine disease prognosis and hopefully lead to therapies that can target each individual's unique cancer cells.

Disorders in which there is a clonal neoplastic proliferation of a multipotent myeloid stem cell are grouped together in the myeloproliferative disorders. The major disorders in this grouping include:

• Chronic myeloid leukemia, with cell proliferation in the granulocytic series

• Polycythemia vera, in which erythrocytic precursors dominate the picture (see the section “Erythrocytosis” in Chapter 10)

• Essential thrombocythemia in which megakaryocytes are the primary cytological feature (see the section “Bleeding Disorders” in Chapter 11)

• Primary myelofibrosis (see the following), a disorder in which the bone marrow is initially hypercellular in multiple cell lineages and then gradually becomes markedly hypocellular with the development of marrow fibrosis

The myeloproliferative neoplasms have a fair amount of overlap in their clinical and hematologic findings, including increased numbers of red cells, platelets, and/or white cells, the presence of circulating immature cells, and the presence of marrow fibrosis. The fibrosis is a reactive response to the neoplastic elements of the bone marrow. Myeloproliferative neoplasms are differentiated from the myelodysplastic disorders because in the myeloproliferative neoplasms, there are few, if any, dysplastic changes in the blood cell precursors in the marrow. The prognosis of the myeloproliferative neoplasms varies depending on the diagnosis. Polycythemia vera and essential thrombocythemia tend to have very long survival and a low incidence of transformation to acute leukemia. Chronic myeloid leukemia and primary myelofibrosis have worse prognoses.

Chronic myeloid leukemia is distinct from the other myeloproliferative disorders in that it contains a specific chromosomal translocation, t(9;22)(q34;q11), also known as the Philadelphia chromosome. This will be discussed in detail below.

The other myeloproliferative disorders commonly contain a mutation in the JAK2 tyrosine kinase gene. JAK2 is a tyrosine kinase involved in transmitting growth signals for several different hematopoietic growth factors. In approximately 80% to 90% of polycythemia and in approximately 40% to 50% of essential thrombocythemia and primary myelofibrosis, the valine at amino acid 617 is mutated to a phenylalanine (designated V617F). This mutation inactivates a domain of the JAK2 protein that normally inhibits its tyrosine kinase activity. The result is that the kinase becomes activated without growth factor stimulation, and this leads to uncontrolled proliferation of the cells. Molecular testing for the V617F mutation has become standard practice for patients suspected of having a myeloproliferative neoplasm.

Chronic Myeloid Leukemia

Description

CML represents approximately 15% of all leukemias in the United States. The median age at diagnosis is 65 years, and there is a slight male predominance, with a male to female ratio of 1.7:1. In CML, the disease begins with a chronic phase that usually lasts for 3 to 4 years after diagnosis. The chronic phase evolves into a more aggressive accelerated phase of the disease. This phase persists for 1 to 2 years in most cases. At least 25% of patients with CML die in this phase of the disease. The remainder progress to an acute leukemia, which is known as blast crisis. The blast crisis typically leads to death within 6 months because it is highly resistant to chemotherapy. Approximately 25% of the patients with CML advance rapidly from chronic phase to blast crisis, without a significant intervening period of acceleration. Hematopoietic stem cell transplantation in chronic phase for patients who can tolerate the procedure is highly effective at curing CML.

CML is characterized by a characteristic chromosomal translocation, t(9;22), also known as the Philadelphia chromosome. Discovered in 1960, this was the first genetic lesion associated with a human cancer. When molecular cloning techniques became available, the t(9;22) was found to produce an abnormal RNA and protein product, BCR–ABL1. BCR–ABL1 is a tyrosine kinase that is constitutively active and leads to uncontrolled proliferation of myeloid cells. In 1996, a drug, imatinib mesylate, was discovered that inhibits the tyrosine kinase activity of BCR–ABL1, and this has led to a revolution in the treatment of CML, which previously relied primarily on interferon-alpha and bone marrow transplantation. Long-term treatment with imatinib can lead to drug resistance however, and new BCR–ABL1 inhibitors are in development to overcome this problem. The only curative treatment for CML is still bone marrow transplantation.

Diagnosis

The diagnosis of CML is based on the morphological appearance of the bone marrow, peripheral blood cell morphology, and cytogenetic and molecular genetic studies. Cytochemistry and immunophenotyping are not particularly valuable in the diagnosis of CML in its chronic phase. This is the stage of the disease in which most CML patients first present.

• Chronic-phase CML—A significant hematologic finding in this phase of CML is a moderate to significant elevation of the neutrophil count, often with all stages of neutrophil maturation detectable in the peripheral blood smear. An increase in basophils is important to recognize, as modest basophilia is an early indication of CML. Approximately 50% of CML patients also have an elevation in their platelet count. The appearance of the bone marrow is hypercellular as the disease progresses in the chronic phase of CML, with an increase in the myeloid/erythroid ratio from 2:1-4:1 to 10:1-30:1. There is complete maturation of the granulocytes in CML.

• Accelerated-phase CML—There is no widely accepted definition for the accelerated phase of CML. The characteristic features of this phase of the disease include splenomegaly, an increase in the proportion of myeloblasts (10%-19%) and promyelocytes in the bone marrow over that found in the chronic phase, basophilia to >20% of the total WBC count, and anemia or thrombocytopenia.

• CML in blast crisis—By definition, when the percentage of blasts is 20% or more in the blood or bone marrow, blast transformation of CML has occurred. The blasts can be of either myeloid or lymphoid lineage; this determination is made by flow cytometry immunophenotyping. Approximately 70% of blast crises are myeloid. CML transforms into ALL in approximately 30% of cases of blast crisis. The immunophenotype is most commonly precursor B-cell ALL.

• Cytogenetics—The Philadelphia chromosome, t(9;22), is present in essentially 100% of CML cases; if the Philadelphia chromosome cannot be demonstrated by cytogenetics, FISH, or molecular studies, another diagnosis should be considered. Blast crisis is usually accompanied by additional cytogenetic abnormalities that appear with clonal evolution.

• Molecular genetics—The diagnosis of CML is still possible in cases that are Philadelphia chromosome negative by using FISH or reverse transcriptase PCR to detect the BCR–ABL1 fusion RNA. PCR can also be used to detect minimal residual disease in patients being treated for CML. Newer techniques are now available to quantify BCR–ABL1 RNA in the peripheral blood or bone marrow. These are being used to assess clinical responses to imatinib and to detect early evidence of imatinib resistance.

Polycythemia Vera

Description

Polycythemia vera is diagnosed by an increase in red cell mass with no apparent cause such as chronic oxygen deprivation (living at high altitude or heavy smoker). Transformation to acute myeloid leukemia is rare, but patients with polycythemia vera are at increased risk for the development of leukemia (see Chapter 10 for additional information on polycythemia vera).

Diagnosis

• Cell counts and the peripheral blood smear—By definition, the hemoglobin, hematocrit, and red cell count are all elevated. Patients often present with microcytosis and a normal hematocrit due to the iron deficiency that develops due to excessive red cell production. Because of this, these patients are sometimes initially thought to have thalassemia trait. The WBC count and platelet count are also often moderately elevated.

• Bone marrow morphology—The bone marrow can appear normal, but is often hypercellular with an increase in red cell precursors. With progressive disease, the bone marrow can become fibrotic.

• Cytogenetics and molecular pathology—Cytogenetic findings are usually normal. Definitive diagnosis is made by demonstrating a point mutation in the JAK2 gene.

Essential Thrombocythemia

Description

Essential thrombocythemia is diagnosed by an increase in platelet count with no other explanation. Platelet counts can frequently exceed 1 million/μL. Patients with essential thrombocythemia can manifest abnormal bleeding or blood clotting, although these complications are not very common. Transformation to acute myeloid leukemia is rare (see Chapter 11 for additional information on essential thrombocythemia).

Diagnosis

• Cell counts and the peripheral blood smear—Diagnosis is made by demonstrating a chronically elevated platelet count. The WBC count and hematocrit may also be moderately elevated.

• Bone marrow morphology—The bone marrow demonstrates an increase in megakaryocytes and an overall increase in cellularity. With progressive disease, the bone marrow can become fibrotic.

• Cytogenetics and molecular pathology—Cytogenetic findings are usually normal. Definitive diagnosis is made by demonstrating a point mutation in the JAK2 gene, which occurs in about 50% of cases. Activating mutations in the thrombopoietin receptor gene, MPL, have also been described in 5% to 10% of cases.

Primary Myelofibrosis

Description

Patients with primary myelofibrosis typically present with marked splenomegaly and some degree of hepatomegaly. The disease affects primarily older individuals. As the marrow becomes fibrotic and cytopenias in the peripheral blood develop, the complications associated with the cytopenias appear. Bleeding from low platelet counts and infections from low WBC counts may be lethal. A minority of patients with primary myelofibrosis (less than 10%) progress to acute leukemia, with a higher incidence in those who are treated with radioactive phosphorus or alkylating agents in the highly proliferative phase of their disease.

Diagnosis

• Cell counts and the peripheral blood smear—The peripheral blood frequently demonstrates a “leukoerythroblastic” picture, with leukocytosis, immature granulocytes including blasts, thrombocytosis, and the presence of immature erythroid cells including reticulocytes and nucleated red cells. The cell counts decline with disease progression.

• Bone marrow morphology—Initially, the bone marrow shows trilineage hypercellularity with megakaryocyte hyperplasia and reticulin fibrosis. With disease progression, there is replacement of the bone marrow by extensive fibrosis allowing little space for hematopoiesis.

• Cytogenetics and molecular pathology—Cytogenetic abnormalities are present in 30% to 60% of patients. Approximately 40% to 50% of patients with idiopathic myelofibrosis have the JAK2 V617F mutation.

Description

Myelodysplastic syndromes include a group of bone marrow disorders with dysplastic (not normal, but not neoplastic) changes of the cells of the myeloid series. In myelodysplasia, the myeloblasts in the bone marrow must represent less than 20% of all nucleated marrow cells, because if there are 20% or more blasts, a diagnosis of acute myeloid leukemia is made. Because the myelodysplastic cells originate from an abnormal stem cell clone that is genetically unstable, there is a tendency for myelodysplasia to evolve into acute leukemia.

Myelodysplastic syndrome can occur as a primary disease or as a secondary disorder following exposure to chemotherapeutic agents or radiotherapy. Most cases of primary myelodysplastic syndrome are found in individuals over the age of 50 years. Many names have been applied to what is now called myelodysplastic syndrome, including preleukemia, refractory anemia (RA), and smoldering leukemia.

Diagnosis

Peripheral blood cytopenias are a hallmark of the myelodysplastic syndrome. As a result of ineffective hematopoiesis, myelodysplasia patients present with the complications of reduced blood cell counts in 1 or more cell lines. The complications include infections from low WBC counts, hemorrhage from low platelet counts, and weakness from anemia. In all forms of myelodysplastic syndrome, the bone marrow biopsy reveals hypercellularity.

A cytogenetic abnormality is found in 40% to 80% of the cases of primary myelodysplasia and 90% to 97% of patients with secondary myelodysplasia. These abnormalities may be useful as prognostic indicators. The most common changes are an interstitial deletion of the long arm of chromosome 5 (5q–) and deletions of chromosome 7 (–7, 7p–, or 7q–).

WHO Classification of the Myelodysplastic Syndrome

The myelodysplastic syndromes include a heterogeneous, but definable group of disorders. A brief description of each the disorders in the myelodysplastic syndrome is provided as follows:

• RA—This is defined as an anemia refractory to therapy. Dysplastic changes are only seen in the erythroid lineage. There are less than 5% bone marrow blasts, and ringed sideroblasts are less than 15% of the erythroid precursors.

• Refractory anemia with ringed sideroblasts (RARS)—This disorder is like RA except that 15% or more of the nucleated RBCs in the marrow are ringed sideroblasts. A ringed sideroblast, as noted in the section “Sideroblastic Anemia” (Chapter 10), is a cell in which at least 30% of the circumference of the nuclear membrane is covered by mitochondria containing iron granules.

• Refractory cytopenias with multilineage dysplasia (RCMD)—This disorder is like RA except that dysplasia is present in 2 or more lineages (lineages being myeloid, erythroid, and megakaryocytic). Auer rods (abnormal inclusions in myeloid blasts) are absent.

• Refractory cytopenias with multilineage dysplasia and ringed sideroblasts (RCMD-RS)—This disorder is like RCMD except that 15% or more of the nucleated RBCs in the marrow are ringed sideroblasts.

• Refractory anemia with excess blasts-1 (RAEB-1)—The major criterion for RAEB-1 is the presence of 5% to 9% of total nucleated cells in the bone marrow as blasts. There can be unilineage or multilineage dysplasia. In addition, the percentage of WBC blasts in the peripheral blood must be less than 5% of nucleated cells. Auer rods are absent.

• Refractory anemia with excess blasts-2 (RAEB-2)—This disease is present if there are 10% to 19% blasts in the bone marrow, 5% to 19% blasts in the blood, or Auer rods in myeloblasts or other neutrophilic precursors. There can be unilineage or multilineage dysplasia.

• Myelodysplastic syndrome, unclassified (MDS-U)—This disease is similar to RA except that dysplasia is present in 1 lineage other than the erythroid lineage. There are less than 5% blasts, and there are no Auer rods.

• MDS associated with del(5q)—Also known as “5q- syndrome,” there are normal to increased megakaryocytes with hypolobated nuclei, less than 5% blasts, no Auer rods, and the sole cytogenetic abnormality of del(5q).

The myelodysplastic/myeloproliferative neoplasm category was created for the 2008 WHO classification. This category is for clonal stem cell disorders that do not fit well into either the myelodysplastic or myeloproliferative disorders. The most common of these disorders is chronic myelomonocytic leukemia (CMML). Other rare disorders in this category include atypical chronic myeloid leukemia, juvenile myelomonocytic leukemia, and an unclassifiable category.

• CMML—This disorder is a chronic leukemia with dysplastic changes in the bone marrow that are indicative of an increased risk for transformation into acute myeloblastic leukemia. Patients with CMML have an absolute peripheral monocytosis greater than 1000 monocytes/μL, less than 20% blasts in the bone marrow, and dysplasia of 1 or more myeloid lineages.

WBCs must be present in appropriate numbers and also function normally. The disorders previously discussed in this chapter are associated with alterations in WBC number, and in some cases, impaired function as well. The 3 disorders presented in the following sections represent examples of WBC functional disorders with no alteration in WBC number. It is for this reason that they are also known as qualitative (as opposed to quantitative) WBC disorders. Many WBC qualitative disorders result in functional impairment and no increased risk for infections. However, other WBC functional abnormalities may be clinically significant and predispose to life-threatening infections.

Chediak–Higashi Syndrome

Description

This disorder is due to a mutation in a lysosomal trafficking regulator. The disorder is characterized by functional defects associated with azurophilic granules in the cells that have these granules. They are particularly prominent in neutrophils and melanocytes. Most patients with Chediak–Higashi syndrome are subject to recurrent infections. Chediak–Higashi patients also have partial albinism because they have defective melanosomes (which provide skin coloration). The platelets from these patients have a defect in storage granules. This platelet granule deficiency may produce a bleeding tendency because release of the granule contents is necessary for the platelets to aggregate and form platelet plugs.

Diagnosis

A personal and family history consistent with Chediak–Higashi syndrome, along with abnormal granules in all granulated hematopoietic cells and lymphocytes, strongly suggests the diagnosis.

Chronic Granulomatous Disease

Description

Chronic granulomatous disease (CGD) comprises a heterogeneous group of disorders in which recurrent bacterial infections can lead to an early death. The WBCs in CGD do not exhibit obvious morphological differences from normal WBCs. However, there are multiple biochemical defects in neutrophil function in CGD that limit their ability to produce peroxide and superoxides that destroy bacteria.

Diagnosis

Patients with CGD have a negative nitroblue tetrazolium (NBT) dye test. In this assay, a yellow dye is oxidized by the oxidative enzymes in the normal granules of neutrophils to form an insoluble blue-black compound detectable by light microscopy.

Myeloperoxidase Deficiency

Description

This disorder results from a defect in the pathway required for generation of free radicals, which are important in the destruction of invading microorganisms, similar to CGD. Although individuals with MPO deficiency may experience recurrent infections, the disorder is benign in most cases. The absence of MPO may be congenital or acquired.

Diagnosis

In patients with MPO deficiency, MPO staining of freshly prepared blood smears will produce only faint staining of the granules in neutrophils.