GENERAL PRINCIPLES
Pancytopenia is a reduction in all blood cell lines, including red blood cells (RBCs), white blood cells (WBCs), and platelets. Patients can present in innumerable ways depending on the severity and type of cell lineages affected. Anemia can cause fatigue, shortness of breath, or lightheadedness. Patients with significant thrombocytopenia can present with bleeding and bruising. Neutropenia is associated with recurrent infections. Cytopenias may result from defects in bone marrow production or from peripheral causes.
Bone marrow infiltration by disease processes such lymphoma, metastatic carcinoma, sarcoidosis, tuberculosis, myeloma, hairy cell leukemia, or in storage disorders (e.g., Gaucher, Niemann–Pick) can result in inadequate production. Vitamin B12 and/or folate deficiency leads to megaloblastic erythropoiesis and defective maturation of granulocytic and megakaryocytic lineages. Copper deficiency is a relatively uncommon cause of pancytopenia.
Causes of increased destruction of blood cells in the periphery include hyper-splenism, autoimmune diseases and overwhelming sepsis. Medications may also affect blood counts. For example, antipsychotics such as clozapine are known to cause agranulocytosis. Impaired production of blood cells is seen in bone marrow failure states, both inherited and acquired. Bone marrow failure is defined as the inability of the bone marrow to produce an adequate number of circulating blood cells. Inherited BM failure syndromes are as described in Table 8-1.1 Acquired bone marrow failure states include myelodysplastic syndromes (MDS), acquired aplastic anemia (AA), and paroxysmal nocturnal hemoglobinuria (PNH).
In most cases, initial laboratory evaluation should include a complete blood count, serum chemistries, peripheral smear and reticulocyte count. If clinically indicated, an evaluation of the patient’s folate and B12 status, or an infectious workup (including HIV, hepatitis panel, other viral or fungal serologies) should be undertaken. If an etiology is not apparent, a bone marrow biopsy and aspirate should be obtained. In cases where a hematologic malignancy is suspected, flow cytometry and cytogenetics performed on the aspirate may be useful.
Treatment and further laboratory or imaging evaluations will depend on the etiology of the cytopenia(s). In cases where a medication is the underlying cause, discontinuation of the offending drug may be curative. Cytopenias resulting from bone marrow infiltration or suppression by other conditions may improve with treatment of the underlying condition. Cytopenias resulting from nutritional deficiencies can be treated by addressing the underlying nutritional deficiencies. In cases where bone marrow failure is the etiology of the cytopenias, treatment will depend on the diagnosis. Features and management of selected bone marrow failure syndromes are described in the following sections.
MYELODYSPLASTIC SYNDROMES
GENERAL PRINCIPLES
Myelodysplastic syndromes are neoplastic clonal stem cell disorders characterized by cytopenias and most commonly a hypercellular, dysplastic-appearing bone marrow. Peripheral blood features include monocytosis, Pelger Huet-like anomaly in neutrophils, circulating immature myeloid or erythroid cells, and macrocytosis. In MDS, the bone marrow is typically hypercellular with “megaloblastoid changes,” atypical megakaryocytes, erythroid hyperplasia, and defective maturation in the myeloid series. Increased blasts or ringed sideroblasts can also be seen. Despite increased cell proliferation, there is also increased apoptosis, leading to the discrepancy between the cellular bone marrow and peripheral cytopenias.
Epidemiology
MDS is considered a disease of the elderly. Approximately 80% of patients are older than 60 years of age at diagnosis. The annual incidence rate of MDS in the United States is estimated to be 3.4/100,000. The median age at diagnosis is 76 years, with only 6% of cases diagnosed before age 50.2 Risk factors include exposure to chemotherapy (especially alkylating agents and topoisomerase II inhibitors), chloramphenicol, radiation, benzene and other solvents, petroleum products, smoking, and immunosuppression. Inherited bone marrow failure syndromes are the primary risk factor for MDS in the pediatric age group.
Classification
The World Health Organization’s (WHO’s) International Agency for Research on Cancer (IARC) revised its classification of MDS in 2008. The revised classification is shown in Table 8-2.3Therapy-related MDS (tMDS) refers to MDS that arises after exposure to chemotherapy agents. tMDS occurs most frequently in patients diagnosed with tumors that are associated with a good prognosis, such as breast cancer, non-Hodgkin lymphoma, Hodgkin lymphoma, and testicular cancer. For instance, 1.7% of patients with breast cancer develop secondary bone marrow disease, with a mean time of 18 months. tMDS and acute myelogenous leukemia (AML) occur in about 5% to 10% of patients with Hodgkin’s lymphoma and non-Hodgkin lymphoma. tMDS differs from sporadic MDS in that it tends to be associated with distinct chromosomal abnormalities. tMDS after exposure to alkylating agents is associated with deletions of chromosome 5 or 7 and occurs 3 to 5 years after therapy. Topoisomerase II inhibitors, such as daunorubicin, etoposide, and tenoposide, cause tMDS/AML with translocations involving the MLL gene at chromosome 11q23, usually manifesting 1 to 3 years after treatment.
Pathophysiology
Patients with MDS exhibit cytopenia(s) despite a cellular bone marrow. Chromosomal analysis suggests that MDS is a clonal disorder. The critical genetic lesions that initiate MDS are not well-characterized. The cytopenias seen in MDS are thought to arise from ineffective hematopoiesis arising from abnormal responses to cytokine growth factors, defects in the bone marrow microenvironment, and impaired cell survival.
DIAGNOSIS
Clinical Presentation
MDS is clinically a heterogeneous disorder. Its clinical manifestations result from marrow failure and cytopenia(s). Sometimes, the diagnosis is made retrospectively after transformation to acute leukemia. Lymph node involvement and hepatosplenomegaly are rare.
Diagnostic Testing
In the absence of other causes, marrow failure (as evidenced by cytopenias) with bone marrow findings of normal or increased cellularity with dysplastic myeloid cells is a cornerstone in establishing the diagnosis of MDS. The CBC often reveals cytopenias, and an elevated mean corpuscular volume. Reticulocyte count is inappropriately low. Peripheral blood smear may show oval macrocytic red cells, hypogranular neutrophils, and giant platelets.
Bone marrow biopsy is essential in the diagnostic evaluation. The cellularity is usually normal or increased, although it can be hypocellular. Dysplastic morphological changes may not be present in all patients with MDS, and the subjectivity of the findings may pose a significant diagnostic challenge. Morphological abnormalities include megaloblastic red cell precursors with multiple nuclei and asynchronous maturation of the nucleus or cytoplasm. Ringed sideroblasts (erythroid precursors with iron-laden mitochondria) are occasionally identified. There is often a predominance of immature myeloid cells, and granulocytic precursors may show asynchronous maturation of the nucleus and cytoplasm. Mature granulocytes are often hypogranular and hypolobulated. Megakaryocytes may be smaller and have fewer nuclear lobes.
Recurrent cytogenetic abnormalities are present in 40% to 70% in de novo MDS and 95% of tMDS. In cases where the clinical and laboratory features are consistent with MDS but the morphological features are ambiguous, a presumptive diagnosis of MDS can be made if a specific clonal chromosomal abnormality (Table 8-3) is present.4 Fluorescent in situ hybridization (FISH) is becoming an important diagnostic tool in the evaluation of MDS. Unlike cytogenetics, which can be performed only in mitotic cells, FISH can be performed in mitotic cells as well as cells in interphase. It also has the advantage of providing quick results and has a high sensitivity and specificity. It can detect clonal cryptic defects in about 3% to 15% of MDS patients with normal cytogenetics, and may detect chromosomal abnormalities earlier in the course of the disease. However, FISH will only detect what is being looked for and hence cannot replace cytogenetics.
TREATMENT
The Federal Drug Administration (FDA) has recently approved four drugs for the treatment of MDS patients: the hypomethylating agents 5-azacytidine (azaC) and decitabine; the immunomodulator lenalidomide for patients with del (5q) subtype; and deferasirox, an iron chelator for treating chronic iron overload resulting from multiple transfusions. Supportive treatment with transfusions and growth factors is also part of MDS management. Allogeneic hematopoietic stem cell transplant (HSCT) is the primary curative treatment for patients with MDS. Features to consider for HSCT include patient’s age, IPSS (International Prognostic Scoring System) score, performance status, comorbidities, and availability of a suitable donor. Higher-risk patients ≤60 years of age should be offered a human leukocyte antigen (HLA) identical sibling transplant at diagnosis (if otherwise feasible), whereas delaying transplantation for several years and prior to disease progression would be appropriate for lower-risk patients. In patients who require reduction of their disease burden prior to HSCT, azaC, decitabine, or participation in clinical trials can be used as bridges to transplant.5 The role of reduced-intensity regimens in patients of advanced age or with other comorbidities remains to be determined.
Lower-risk MDS
For patients with lower-risk MDS, treatment is aimed at reducing transfusions, restoring effective blood cell production and maximizing quality of life. For lower-risk MDS patients with symptomatic anemia, treatment follows one of several pathways. In patients with MDS del(5q), lenalidomide, a derivative of thalidomide, is the treatment of choice. In this population, 70% experience transfusion independence or a decline in transfusion needs when treated with lenalidomide. Lenalidomide, like thalidomide, inhibits angiogenesis, alters cellular immune responses, modulates various cytokines, and has direct antileukemic, antiproliferative effects. In addition, lenalidomide also enhances erythropoietin (EPO) receptor signaling. It is more potent and has a favorable side-effect profile compared to thalidomide. Its dose-limiting side effects include neutropenia and thrombocytopenia.
In other lower-risk MDS patients lacking del(5q), erythropoiesis stimulating agents (ESAs), which include epoetin and darbepoetin, may be appropriate. Patients with low transfusion needs, defined as <2 units of packed red blood cells (PRBCs) monthly, and a low baseline serum erythropoietin level (<500 IU) have a 74% chance of responding to ESAs. Consequently, ESAs, with or without granulocyte colony stimulating factor (GCSF), are appropriate initial treatment for these patients.
On the other hand, patients with higher transfusion needs (≥2 units of PRBCs) and high serum erythropoietin level (≥500 IU) have only a 7% chance of responding to ESAs. Patients with age ≤60 years, hypocellular marrows, HLA-DR15 histocompatibility type, or PNH clone positivity, have a good probability of responding to immunosuppressive therapy (IST) with antithymocyte globulin (ATG) or cyclosporin A. Those who are deemed unlikely to respond to IST should be treated with hypomethylating agents. Lenalidomide can also be considered.
Higher-risk MDS
For patients with higher-risk MDS, the goals of treatment are similar to patients with AML, and include attaining a partial or complete remission, prolonging survival and also maximizing quality of life if patients are candidates for high-intensity therapy, allogeneic HSCT is recommended if a suitable donor can be identified. Patients without a suitable donor should be treated with a hypomethylating agent such as azaC or decitabine, or high intensity chemotherapy. For higher-risk MDS patients who are not candidates for high-intensity therapy, treatment with hypomethylating agents is appropriate.
PROGNOSIS
Evolution to AML occurs in 10% to 50% of all cases of MDS; it varies with the MDS subtypes and correlates with the survival duration. The IPSS for MDS (Table 8-4) developed in 1997 continues to be one of the most widely used prognostic tools, despite its shortcomings.6 It should be noted that the IPSS is only validated in previously untreated patients. Furthermore, in 2001, the WHO changed the acute leukemia-defining marrow blast threshold from 30% to 20%, making the IPSS appear dated. Much debate revolves around the classification of the patients with 20% to 30% blasts, who appear to represent a heterogeneous group with characteristics that differ from classic AML. The IPSS score does not take into account the severity of cytopenias, and has been criticized for overemphasizing the significance of marrow blast proportion while underemphasizing high-risk karyotypic findings. Lower-risk MDS patients (RA, RARS, RCUD, RCMD, MDS-U MDS del(5q), IPSS low or Int-1) have an estimated survival of 3 to 10 years. Higher-risk MDS patients (RAEB-1 or RAEB-2, IPSS Int-2 or high) have an estimated survival of <1.5 years, and a high rate of AML transformation.7
APLASTIC ANEMIAS
GENERALP RINCIPLES
Aplastic anemias (AA) refer to conditions in which normal hematopoietic tissue is replaced by fat. They are characterized by pancytopenia and a hypocellular bone marrow in the absence of bone marrow infiltration and increased reticulin deposition. AA can be acquired or arise in the context of an inherited bone marrow failure syndrome. AA can coexist with other conditions such as PNH (discussed in the next section) and T-cell large granular lymphocyte (T-LGL) disease. Approximately 40% to 50% of patients with acquired AA have expanded populations of PNH cells.8
Epidemiology
Acquired AA is a rare disease. The incidence is estimated to be about two cases per million per year in Western countries, and about two- to threefold higher in Asia. Almost half of the cases occur during the first 3 decades of life.8
Classification
AA can be acquired or inherited. Table 8-1 outlines several forms of inherited AA.1 In the presence of an empty marrow, pancytopenia, and transfusion dependence, the severity of the disease is based on the absolute neutrophil count (ANC). In nonsevere AA, the ANC is >0.5 × 109/L. In severe AA, the ANC is between 0.2 and 0.5 × 10 9/L. In very severe AA, the ANC is <0.2 × 109/L.9
Etiology
The genetic aberrations associated with inherited bone marrow failure are listed in Table 8-1. The rarity of acquired AA is accounted for by a combination of infrequent exposure events, diversity of predisposing genetic factors, and individual differences in immune response. Table 8-5 lists some of the factors thought to be associated with acquired AA.10
Pathophysiology
The pathophysiology of acquired AA is an immune-mediated attack on the hematopoietic stem cells in most cases, caused by activated cytotoxic T cells bearing the Th1 profile. These activated T cells produce cytokines such as interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α). Fas ligand expression is induced by IFN-γ and TNF-α. Binding of Fas ligand to the Fas receptor on hematopoietic stem cells could contribute to marrow aplasia by triggering apoptosis. The reason for T cell activation remains unclear. It is possible that an inciting event like an infection, toxin, or a drug exposure provokes the aberrant immune response. HLA-DR2 is overexpressed in patients with AA. Recent data also implicate intrinsic defects in hematopoietic stem cells. Mutations in the genes for telomerase, TERC and TERT, have been described in patients without overt clinical stigmata of dyskeratosis congenita. Telomere shortening is observed in one third to one half of patients with AA. Accelerated telomere shortening may result in premature death of rapidly proliferating cells.
DIAGNOSIS
Clinical Presentation
Patients with AA present with symptoms related to pancytopenia. The presence of weight loss, pain, loss of appetite, or fever suggests another diagnosis. Physical examination usually reveals pallor, mucosal bleeding, petechiae, and ecchymoses. The presence of lymphadenopathy, hepatomegaly, or splenomegaly strongly suggests another diagnosis such as lymphoma, leukemia, or bone marrow infiltration.
Diagnostic Testing
The diagnosis is established by bone marrow aspiration and biopsy. The findings include a profoundly hypocellular marrow with a decrease in all cellular elements, with marrow space being replaced by fat cells and stromal elements. The residual hematopoietic elements are morphologically normal. There is no increased reticulin formation or infiltrative elements. Evaluation for other etiologies of pancytopenia includes viral serologies for hepatitis, CMV, EBV, parvovirus, HIV, and herpes. Serum B12 and folate levels should be determined. As an underlying cause of AA is Fanconi anemia (FA), even in adults without other classic features of FA, diepoxybutane (DEB) or mitomyin C testing to exclude chromosome fragility should be considered. Evaluation for the presence of a PNH clone is also part of the workup. T-LGL, a rare condition characterized by an increase in the number of circulating T cells bearing the CD57 activation marker of effector/cytotoxic T cells, should be considered if increased large granular lymphocytes are noted on examination of the peripheral blood smear or if the patient has a history of rheumatoid arthritis.
TREATMENT
Management of AA includes supportive care as initial treatment to sustain an acutely ill, pancytopenic patient. Immunosuppression and allogeneic HSCT are the main therapeutic approaches.8,9
Supportive care. Patients with symptomatic anemia will need transfusions. Patients with symptomatic thrombocytopenia or a platelet count of <10,000 should be given platelets. Blood products should be irradiated to prevent transfusion-associated GVHD. In patients who are considered for stem cell transplantation, only CMV-negative products should be administered to CMV IgG-negative patients, and blood products from family members should be avoided to prevent alloimmunization. EPO and myeloid factors are not used as a mainstay of treatment. No significant survival in survival has been seen in patients receiving G-CSF as compared to those who did not receive G-CSF.
Immunosuppression. ATG with cyclosporine is indicated as first-line therapy for nonsevere AA patients who are transfusion dependent, severe AA patients >40 years of age, and severe AA patients <40 years of age who lack an HLA-identical sibling donor. Response to ATG occurs in around 50% of patients by 3 months, and 70% to 75% by 6 months. Relapses occur in up to 30% to 35% of patients when cyclosporine is withdrawn at 6 months.
HSCT. Patients with severe AA <40 years of age with an HLA-matched sibling donor should be offered HSCT as first-line treatment. The 5-year survival is 77%. In children and minimally transfused patients, survival of 80% to 90% can be routinely achieved. Acute GVHD occurs in about 20% to 30% of patients. Chronic GVHD is a major cause of morbidity and mortality in patients who survived more than 2 years post transplantation, and life-long immunosuppression is often needed. Chronic GVHD occurs in about 30% to 40% of patients. As a matched sibling donor is available in only about 20% to 30% of cases, alternative sources of hematopoietic stem cells have been sought. HSCT from unrelated donor carries higher morbidity and mortality than HSCT from a matched sibling donor, and are therefore reserved for patients who lack a matched sibling donor and who failed to respond to one or more rounds of immunosuppression.
PROGNOSIS
Without treatment, patients with severe or very severe AA will eventually succumb to infections or hemorrhagic complications. Spontaneous remission can be seen with drug-induced AA and usually occurs within 2 months of presentation. Overall survival after immunosuppression for AA is approximately 75% at 5 years. This equates with survival after HSCT. For patients treated with immunosuppression, long-term follow-up data indicated an actuarial probability of developing hemolytic PNH at 11 years of 10%, MDS or AML 8%, and a solid tumor 11%.
PAROXYSMAL NOCTURNAL HEMOGLOBINURIA
GENERAL PRINCIPLES
PNH is an acquired disease characterized by nonmalignant clonal expansion of one or more hematopoietic stem cells that have undergone somatic mutation of the PIG-A gene. PNH can present with bone marrow failure, hemolytic anemia, smooth muscle dystonias, and thrombosis. PNH can arise de novo or in the setting of AA.11
Pathophysiology
The protein encoded by the PIG-A gene is essential for the synthesis of glycosyl phosphatidylinositol (GPI), and therefore GPI-linked proteins are lacking in the PIG-A mutant clone. PNH RBCs lack two GPI-anchored complement regulatory proteins, CD55 and CD59. Hemolysis in PNH results from increased susceptibility of PNH RBCs to complement-mediated destruction. Intravascular hemolysis releases free hemoglobin into circulation. Free plasma hemoglobin scavenges nitric oxide (NO) and the depletion of NO at the tissue level is postulated to account for multiple PNH manifestations, including esophageal spasm, male erectile dysfunction, renal insufficiency and thrombosis. The PNH clone is present in a considerable proportion of the general population without symptoms. In patients with PNH, the clone is expanded significantly. It is postulated that PNH patients have some degree of marrow failure and the PNH clone is selectively protected from bone marrow injury as result of the lack of GPI-linked proteins.
DIAGNOSIS
Clinical Presentation
The clinical manifestations of PNH are intravascular hemolytic anemia, marrow failure, and thrombosis. Bone marrow failure can be transient, mild, or severe. Thrombosis usually involves the venous system and occurs in about 40% of PNH patients. Thrombosis can occur in unusual sites such as intra-abdominal veins. The clinical course is unpredictable and patients can have spontaneous remissions. PNH can present with or without evidence of another disorder such as AA or MDS. Subclinical PNH (without clinical or laboratory evidence of hemolysis) can occur in association with other bone marrow failure syndromes.
Diagnostic Testing
Flow cytometry using monoclonal antibodies against specific GPI-linked proteins is the most sensitive and specific test to identify the PNH clone. Fluorescein-labeled proaerolysin variant (FLAER) is increasingly used as a flow cytometric assay to diagnose PNH. The hemolysis is intravascular (high reticulocyte count, increased lactate dehydrogenase and unconjugated bilirubin, and decreased haptoglobulin) and is Coombs negative. Iron studies are needed to evaluate for iron-deficiency anemia, which can result from renal loss of hemoglobin. Bone marrow biopsy is helpful in assessing for marrow failure.
TREATMENT
There are no clear evidence-based indications for treatment of PNH. For asymptomatic patients or those with mild symptoms, watchful waiting is an appropriate approach. For patients with underlying AA, treatment is directed toward the underlying bone marrow failure. Indications for treatment in classic PNH include disabling fatigue, thromboses, transfusion dependence, frequent pain paroxysms, renal insufficiency, or other end-organ complications. Corticosteroids can improve hemoglobin levels and reduce hemolysis in some PNH patients, but its long-term use is limited because of toxicity. Complement inhibition and HSCT are established effective therapies for PNH.
Complement inhibition. Eculizumab, a humanized monoclonal antibody against complement C5, inhibits terminal complement activation.12 It has been approved by the FDA for use in PNH. Eculizumab is effective in decreasing intravascular hemolysis, need for blood transfusions, and risk of thrombosis. Eculizumab is administered intravenously at a dose of 600 mg weekly for the first 4 weeks, then 900 mg biweekly starting on week 5. It is well tolerated, but must be continued indefinitely as it does not treat the underlying cause. Its serious adverse effects include risk of infection by encapsulated organisms. Patients receiving eculizumab should be vaccinated against Neisseria meningitides prior to starting therapy.
HSCT. Allogeneic HSCT remain the only curative therapy for PNH, but it is associated with significant morbidity and mortality. Currently there is no definite indication for transplantation. Patients with life-threatening thrombosis and underlying severe BM failure should be considered for transplantation.
Treatment of thrombosis. Thrombosis is a life-threatening complication of PNH and should be treated promptly with anticoagulation. However, anticoagulation is only partially effective in preventing clots, and treatment with eculizumab should be strongly considered in patients with thrombosis. The duration of anticoagulation after initiation of eculizumab is controversial in these patients. Likewise, the role of prophylactic anticoagulation in PNH is also controversial.
PROGNOSIS
The natural history of PNH is highly variable. Median survival is 10 to 15 years. Thrombosis is the leading cause of death. Patients with PNH may also develop life-threatening bone marrow failure, MDS, or leukemia. Patients with AA and a PNH clone typically do not exhibit signs or symptoms of PNH early in the natural history of their disease, but many will experience further expansion of the PIG-A mutant clone and progress to classic PNH.
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